Time travel to the past hypothetically possible?
Yet another thread about time. I was thinking yesterday of a very vague idea that I'd like opinions on. So then if we took a "snapshot" of this very moment with it's totality, that being: The position of every single object, cell and et cetera. And had the ability to manipulate matter in such a way that we can reposition new "environmental" circumstances into the ones that we have snapshotted, would that not be considered time travel? If anybody ever has watched "Watchmen" and know of Dr.manhattan I ask this question as regarding his fictional abilities. Those being the ability to manipulate a surrounding environment to a total extent, whatever that may be.
Comments (212)
This just popped into my head: I always believed that animals, specifically predators - big cats especially - had a sense of time which if it isn't chronos is definitely kairos for they have to, as I initially assumed, know when to begin their chase for the selected prey animal. This, however, could be an illusion because there's the possibility that the chase begins not in a temporal context wherein the lion/tiger, in its mind, comes to the conclusion that "yes, this is the right moment to begin my chase" but what actually goes on in the lion's/tiger's mind is a spatial calculation as in "this is the optimum distance for a successful chase". The two - temporal vs spatial reasoning vis-à-vis hunting - appear to be indistinguishable. The question that naturally arises is, can this be true of us too? In the simplest sense, could time be space? :chin:
Hypothetically yes but the laws of physics as we know it do not allow travel into the past.
https://en.wikipedia.org/wiki/Time_travel
Time travel into the past It is therefore theoretically not possible, but due to lack of our knowledge about universe your hypothesis is not completely invalid.
I would say no because then we can assume "non movement" trough space as stopping (or slowing down) the time which isn't the cause.
A question may arise, what about inanimate nature? it is subject to time as well.
Imagine yourself deer hunting with a compound bow. You see a deer but you realize it's not in range. You, as quietly as possible, close in on the hapless deer. It's now inside your bow's kill zone. What goes on inside your head? Do you tell yourself, "this is the right moment to release my arrow"? or do you think, "this is the right distance for a killshot"? Could a disinterested observer figure out which of the two thoughts mentioned above determined your actions? If yes, how? If no, I rest my case. Sorry for repeating myself but I needed to clarify things to myself and to you too.
I may say "this is the right distance for a killshot?"
Isn't my thinking in this sense merely my judgement? a mental ability.
How does my judgement about distance affect time?
We know measuring distance is not same as measuring time because of speed factor (ex. the speed of my arrow), therefore we could also say "this is the right moment to release my arrow?"
But doesn't this depend on relative speed of the arrow and the speed of the deer?
Isn't relative speed affecting both scenarios?
We know relative speed can make our perception about time wrong, did you ever walk train station in opposite direction of the moving train?
You must have noticed the station moving and the train staying in place right? :smile:
Does the train station example affect time or distance or something else? and if so why?
You cannot, but you can imagine it. Time is what is and what is unfolding. There is no traveling in time, only change that we feel, like molding a piece of clay.
Yes, had same idea few years ago it is entirely possible we do similar thing in computers when we do a "save" or "checkpoint" the only thing is even if knew all variables needed for a specific state of a universe, how do we push them to atoms? I like to call it state traveling much more fitting and theoretically speaking once we invent a machine to capture and push state through whole wide universe we would be able to calculate past based on it to its correct form then universe would become huge game where we change variables to state we need, sounds fun :)
Yes that is correct form of "time" traveling, it's just hollywood concept for people to imagine it
What about sending a signal into the past or future rather than a macroscopic object? This seems more possible, less impeded by classical physics, if a form of energy wave that transmits information fast enough is discovered. What if we could turn on a device and get detailed engineering blueprints from thousands of years in the future or receive messages from distant parts of the galaxy?
It would have to be via a kind of wave that is independent of electromagnetic matter, maybe dark matter, perturbing faster than the speed of light or penetrating more deeply into reality's underlying structure. Whether a technology of time traveling waves is possible depends on the orientation of thus far unknown matter to known matter and the logistics of generating these waves, but it intuitively seems to me as if some mechanism of this type must exist. Maybe studying the way brains transmit energy would be a good start, the technology could initiate with a more substantive model of near instantaneous and retroactive causality in nature. I think its more likely we can obtain a digitalized signal from the future because there are no receiver devices in the past. Of course you have to make sure that it wouldn't leave a path of devastation in its wake, but a harmless incarnation probably exists.
For instance, a society or country can make new time contract that from tomorrow, it will be year 0, and a day will be 40 hours, and a month will be 100 days, and run it like that. I think historically Cambodia had done it sometime in 1970s. And initially people will get confused or feel chaos on the time perception, but they will get used to it.
So, yes time travel is possible, but only in memories and imaginations and the movies. No, it is not possible in real life.
What we have is eternal present called "Now", from which no existence can escape until their consciousness fades away.
This is a really good movie incorporating your idea: Prince of Darkness
All causal events stemming from the time travel will be recorded as having an unexplained cause.
I have read some stories of alleged time travel, and it seems to be possible to fit them into a consistent picture of the universe and reality.
https://www.indiatimes.com/culture/who-we-are/7-real-accounts-of-time-travel-that-ll-leave-you-questioning-everything-258251.html
Quoting unintelligiblekai
I don't think that would be considered time travel, you would still be moving forward through time while you change the environment. Theoretically, if you also knew the exact placement of every particle in the past you could recreate a past situation, but recreation would not be traveling back and viewing it in time it actually happened. The only way to see into the past would be to somehow transfer yourself to a far distant place with a telescope to view earth as it was in the past. Also you can already travel forward in time by going very fast.
It's of course not practically possible.
If you consider it in terms of photons time travel is not possible.
Suppose on Jan 1, 2000, there is a light source at A. Photons travel to B.
Now a time traveler leaves on Jan 1, 2010 and appears on Jan 1, 2000, at C, the mid point between A and B.
The time traveler blocks the light and it does not reach B.
So, does the light reach B or not?
It still wouldn't be time travel. It would be recreating the past in the future. Just like recreating a natural diamond perfectly in a lab, doesn't make another natural diamond, rather it is a natural appearing lab grown diamond.
This. You can't go to the past. You can only recreate a setup of matter and energy that existed in the past. Once you did, it would then continue identically as it did in the past unless any specific alterations were made.
The idea of time travel is more easily understood in terms of time travel to a past or earlier time than the present time. Let's say that a time machine was first invented at the present time, tn, and is to be used to return to an earlier time, te. This means - prior to any use of the newly invented time machine - that there is an "original" version of time, te, which is pre-time-travel (and contains no time traveller). Once the time machine is used, there will then be a second version of that same time, te, which is post-time-travel and contains the addition of the time traveller. That is, the use of the time machine and the introduction of time travel means that a second timeline branches off and exists concurrently with (or as a parallel universe to) the first "original" timeline. This is required in order for the concept of time travel to make sense. If you want to use the time machine to go back and kill Hitler, then there needs to be an original timeline in which Hitler exists and will do, is doing or has done his evil deeds before anyone can go back in time to kill him.
The same holds for time travel to a future time, assuming that the events of the "original" future timeline would have played out a particular way prior to any time travel.
I don't really understand the argument that you must recreate the past exactly as it already did occur or that you cannot logically go back in time to kill your grandfather. These assume that there can only be one timeline, original or otherwise. But I don't think that assumption is consistent with the logical concept of time travel.
Let's suppose I build a time machine and use it to travel to a time before my birth. What makes it impossible? I take it your view is based on the immutability of a single timeline, but that's never been proven and I can find no good reason why it must be assumed.
Quoting Corvus
It has been imagined in numerous works of fiction, so it does not appear to be unimaginable.
Quoting Corvus
The question of the OP is whether time travel is hypothetically possible. I don't see why not.
It's basically like seeing white noise on an old TV, that's the chaos of probabilities and then all those points in that white noise collapse into a single point. If you go back in time, which point is the correct point that you would define was the "true" past one? It's an absurd attempt as all points are true until it collapses into just the one.
Why would you assume that? That's very abstract. How about something more simple: it's impossible, as far as we can tell, because there's no known physical phenomena that could allow us to do it.
It's based on what I've read of time travel paradoxes such as the Grandfather paradox.
Quoting flannel jesus
Isn't that just saying that we don't have the technology or knowledge to time travel? This doesn't mean that it is hypothetically impossible.
It seems the whole imagination has been based on the wrong assumption that the past and future are some sort of geographical destinations such as Tokyo, NY, Paris ... etc, which is not.
Another wrong assumption is that time is some type of physical distance laid out like a road or highway.
The reality is that time is an illusion, and there are only Durations (already proved and declared by Newton), and the past and future are concepts, not geographical places you can arrive at or depart from.
You cannot travel into a place where the destination doesn't exist. We are all nailed into the present until deaths under the universal law.
Quoting Luke
Quoting Luke
Sure one can imagine anything, but we are just letting them be aware that it is imaginable (at stretch), but impossible in reality from the logical and metaphysical point of view. :)
What makes these assumptions wrong? What argument supports your assertion that times are not "geographical places you can arrive at or depart from"?
Quoting Corvus
Whatever time I am at is the present time for me. Therefore, if I were to build a time machine and use it to travel back 100 years, then it would be the present time for me when I depart today and still the present time for me when I arrive 100 years ago.
Can you travel into your happiness or hopes? There is no such a place as the past or future. There are geographical places such as the countries, cities and towns, not the past or future. You cannot escape the present. It is a universal law, which the whole universe and its contents must abide by.
Quoting Luke
And you will be waking up from your dream or imagination. :D
I could say that I am "here" at my current location (or "geographical place"), whereas earlier I was at a different location and later I might be at a location different to both of these. While I am at each location, I can sensibly say that I am "here" at each location. This is no different to being at the "present" at different times. I always find myself "here" no matter the place and at the "present" no matter the time. Although you can neither escape "here" nor "the present", this does not entail that you cannot depart from or arrive at different places or times.
The Grandfather paradox might not be completely binding. Give it some thought.
On my view, there is simply no paradox. The timeline branches off into two parallel timelines once time travel first occurs. The Grandfather "paradox", supposedly, is one of contradiction.
The Wikipedia article on time travel states:
The SEP article on time travel states:
Let's say Bob travels back in time to 1990 with a plan to kill his younger self. When he arrives, there will be two versions of Bob in 1990: young Bob who is not a time-traveller and old Bob who is a time-traveller. According to the Grandfather paradox, if Bob were to kill his younger self, then he would no longer exist. But why? There were two version of Bob in 1990 and only one of them was killed. Why would older, time-traveller Bob suddenly vanish into thin air?
I understand that young Bob can now no longer grow up to build a time machine, but so what? He already did that. And now he continues to live out his existence as old Bob from 1990 onwards because that is the logical sequence of events following the time travel event. The time travel event creates a second timeline (from 1990 onwards) in which young Bob no longer goes on to build a time machine, but on the first timeline he did build a time machine and went back and killed young Bob.
According to what I've read, there cannot even be two Bobs in 1990 because that causes a contradiction (e.g. Bob is in two places at once). But of course there must be two Bobs in 1990 if Bob is to time travel at all. They're not both the same version of Bob obviously (one is a time traveller), so it seems wrong to say that there is any contradiction.
When you say "I am here." in the each different locations, you are not saying anything about the physical geographical locations themselves, but you are stating that YOU are in a location.
Anyhow, it wouldn't be a concept such as happiness, hopes, past or future, you would be in physically.
And no matter how far back or forward, you imagine to have gone to, it would be always the present, because everything happens in present. You cannot escape from it.
Another problem with time travel would be, that EVEN IF you might have gone to the past or future, but the rest of the universe will still stay at the present. There is no point of you going back to 100 years back, if the rest of the universe stays at the present. It is just physical, metaphysical, logical and QM impossibility to wake up all the deads from the graves, and rebuild all the castles which had been demolished, and reinstate all the past monarchies and governments into the power .... etc.
The only way to plausibly think about time travel would be thinking the possibility of the existence of so many different possible worlds which are running at different times. And if you proved their existence, then you would have to find out how to get there from the actual world to one of the possible worlds of different times - say 100 years back or 2000 years back or 200 years forward. But are there such possible worlds in real existence? QMly oh yeah why not, Logically yes, Metaphysically maybe, Physically Nope.
Likewise when I say "I am at the present time" or when you talk about the present: you are not specifying anything about the times themselves, but you are stating that YOU (or we) are at a particular time.
Quoting Corvus
Right, I agree. But how does this help your argument against time travel? I'm happy to refer to earlier and later times instead of past and future times if you'd prefer.
Quoting Corvus
Why not? That's what time travel is.
Quoting Corvus
This is not what time travel is. A time traveller does not bring (objects and events from) other times into our present time. Rather, a time traveller leaves our present time to arrive at other times.
The whole point of time travel is about going to the place at the time of the past or future with the historical or futuristic people in real flesh in the reality at the time.
What would be a point time traveling to Königsberg of 1776, and on your arrival at the place, you see the modern military bases with the nuclear arms all over the place instead of Immanuel Kant taking his daily walks around the town centre?
What would be the point of traveling 2200 years back to the ancient Greece, if you met up with a bunch of Chinese tourists with mobile phones taking selfies in front of the relics, instead of seeing Plato and Socrates talking to his students in the Lyc?um?
I agree. I don't understand this argument:
Quoting Corvus
Time travel has nothing to do with waking the dead or rebuilding demolished castles.
Well, Kant has been dead for over 200 years. How else could you meet him, if you are going back to his time. Someone has to wake him up from the grave, and reinstate him as the professor of the university, and make the universe as it was in 1776. :nerd:
Kant is alive in his time. I'd be going back to his time.
:chin: :roll: :yawn:
There is no need to "make the universe as it was in 1776" or to raise Kant from the dead. If I travel to 1776, then that was a time when Kant was alive.
Your argument is like saying that in order to travel to Greece, you need to recreate Greece at your current location. What really happens is that you travel to Greece, you don't bring Greece to you at your current location. Similiarly, with time travel, you travel to another time, you don't bring the other time to you. Therefore, there is no need to "recreate" the other time in our time, or to "make the universe as it was in 1776" in our time in 2024. You are travelling to another time, not recreating it here and now. Kant was alive in 1776 so if you were to travel to 1776 then it would not be possible to raise Kant from the dead, because he would not be dead.
Your premise "If I travel to 1776" is an impossibility from the reality of 2024, and therefore it is false. Your conclusion is true in that 1776 was the time Kant was alive.
Even if your conclusion was true, but because your conclusion was drawn from the false premise, your proposition is invalid.
Why do you say it's impossible? It is possible that someone will invent the technology for time travel in 2024.
In what sense is it possible, or under what ground is it possible?
I already answered that. It's possible that someone could invent the technology for time travel.
You said it was impossible and that my premise was false. The onus is on you to explain why it's impossible.
I thought it was obvious. Your statement has too many unclear terms. When it says someone could invent, who is someone? Does he exist in the real world? What is his name? Where is he from? What does he do?
The technology, which technology is it? What is the technology based on? How does it work?
And time travel? What do you mean by time travel? Does time exist? In what form does it exist? Travel? what do you mean by travel? Are you physically going somewhere? Where is the destination?
So, you statement is made up with the terms which doesn't have clear meanings. Therefore your statement is not true, and the negation of the statement is true. Because the negation of the statement is true, your statement is false. How is that? :smile:
For you to refute my argument, you must clarify all the unclear terms in your statement with concrete clarity in meanings, and we can start again thereat.
Non sequitur. If it's an unclear statement, how does it follow that it's not true?
Quoting Corvus
Very poor. You've offered zero support for your assertion that time travel "is an impossibility from the reality of 2024".
It is not true, because its negation is true.
Quoting Luke
Support is not our goal of argument. The goal of the argument is finding out which statement is true. It seems clear that yours is not true.
P.S. : You have not managed to clarify any of the unclear terms in your statement, which are the base of the invalidity, and entailing the ground for its falsity.
You said it wasn't clear what the statement or its terms mean. How do you know it's not true if you don't know what it means?
I knew the negation of the statement was clearer, and it gave the ground for the truth, which entailed the falsity of your statement.
Absolute nonsense. Goodbye.
That's a poor argument and conclusion. Good day. :)
I will reconsider your statement for its truth, if you come back with the clarifications for all the mysterious terms you used in it.
Your statement is a typical case for a logical form itself cannot verify the truth / falsity of statements. You must investigate the contents i.e. concepts and ideas in the statements or propositions for its clarity and soundness for the fitness as qualifying the elements for legitimate truth bearers.
If you are using unclear, mysterious or false terms or ideas in statements or propositions, it should be pointed out, and the whole claim must be classed as invalid, unsound or false before checking out the logical forms or structures.
1. Travelling to another point in time from the one you started from.
2. That precedes the rest so will leave aside.
3. Doesn’t matter. Time might not exist but the concept of another point in history remains. Problems remain to be solved but it’s not as if a normal person can’t grok this concept easily.
4. Travel means point A to point B or further. The actual medium is dependent on the medium through which you’re travelling. In this case it may well be zero(seen Event Horizon?). But who knows.
5. ………1776. I didn’t get any impression there was a geographical element to the travel discussed.
Unsure why you’re having so much trouble. I don’t personally think this is going to happen. But your impossibility claim seems more to be you having trouble with holding a few different things together in the idea (location, medium, dimensionality etc..
But hey I could be wrong. I just had no issue understanding the argument.
Time is a concept in mind. Travel means physical motion describing going from physical location A to B. How do you travel in the concept to another physical location, unless travel means something else such as an extremely odd imagination? Or time means some other object such as a town or city called Time?
If you’re a Kantian or similar about time. Not everyone is. Beside this, time as a concept describes a pattern which actual does obtain among material and bodies. Just move through the pattern of materials.
Unless you deny the external world entirely, changes exist. Choose your “point in time” based on the “previous state of affairs” you’re after. No need for dates - but would require a more god-like knowledge of history
Recreating a piece of some past state. Indeed, this isn't time travel being described.
I can build a new 1928 Studebaker, even giving it the same serial number as one made in that year. Has that car time traveled or is it just a new thing? I satisfied the conditions of the OP by doing so. Is it even a Studebaker if I built it instead of the defunct company?
There's several physics violations made by the OP, mostly that the state of some system can be fully measured (violating Heisenberg uncertainty), counterfactuals, and violations of entropy, the latter of which can be fixed by recreating a finite state, just a system in a box, not everything.
The question for the OP scenario then becomes, how is the thing created in the box you? Suppose you recreate a 'you' while you're still around, outside the box. Clearly the created thing in the box is not you. Nothing has 'traveled' into the future.
That said, yes it has. If you look at the state of Earth in 1990, you'll find me there. Have I time traveled to 1990? It seems I have. The statement presumes there is a 1990 in existence to examine, which pretty much means presentism is abandoned, which says only today exists.
Quoting CorvusThis is what I mean. Corvus seems to assume presentism with this statement. The whole notion of time travel seems to assume otherwise, that there are 'other times' available as valid destinations.
Quoting CorvusFunny that you will nevertheless travel to tomorrow. I plan to see you there.
People talk about time dilation being time travel. It isn't any different than doing the same thing sitting still. You get to 'the future' either way, assuming you live long enough to get to the target destination.
On a different note, closed time loops are valid solutions to Einstein's field equations. So are tachyons, and nobody has any reason to suspect either actually exists anywhere, but it isn't mathematically impossible. They don't for instance violate things like the grandfather paradox, and don't require branching of timelines.
Yes, my view of time is similar to Kantian time. It is a concept in mind. Time doesn't exist in the physical world like space does.
Quoting AmadeusD
Do you claim that change is the same thing as time? No, one can deny the existence of time without denying the existence of the world. They are totally different things altogether. The world exists physically, but time exists in mind.
I don't think it is me who has difficulties in understanding the issue. It was Luke who had to prove that his statements were logical. I had clear arguments against them.
So what is your own definition of time, and time travel? Can you travel in time physically, or is it in some other way?
If you insist that you can travel into the past or future in your imagination, yeah I would say it might be imaginable within your imagination. I was only pointing out the impossibility of time travel in the physical world.
Quoting noAxioms
Strictly speaking there is no tomorrow in reality. What you call tomorrow is in your imagination as a concept or idea. There is only "Now" for the whole universe and its members. :) So you might say, we are travelling into tomorrow, but in actuality you are awaiting for another "Now" which will be in next 24 hrs of duration.
I agree with this, as a Kantian definition. But I do think there must be an actual “something” from which our senses infer a consistent ratio of change from moment to moment. I suppose whatever that medium is, is what I refer to as “time”. Perhaps it’s something not perceptible which is why we’ve evolved “time” as a figure of mentation.
Quoting Corvus
I am leaning toward “no”. Time being immaterial, change being material in some sense or another. The “previous states of affairs” may obtain somehow, though I can’t answer the how.
Quoting Corvus
Unsure precisely but I view it similarly to the Tesseract in Interstellar to use a visual metaphor. All change occurring in tandem - but, and this is the important part - in order of appearance (as such). Appearance “in time” doesn’t necessarily speak of duration. Our position in it requires duration - hence developing the mental faculty for it.
As always, these are vague, young, naive ideas I’m having. I’m not trained or anything yet
Trusty yes.
I generally agree. Time travel exists, but only to the future, never the past (since, as stated) there is no "past" to travel to.
Quoting LuckyR
I personally don't insist that there is no "past' to travel to. I give equal ontology to all of spacetime, not just one 3D slice of it. Reverse time travel (as typically envisioned) is not possible because it would constitute transfer of information outside of somebody's future light cone, something which relativity forbids, and something which has never been demonstrated .
Your opinion, not mine. "Tomorrow" is a relative reference, sort of like (one km to the east). There is no objective location that is 'one km to the east', but relative to any given reference location in a place where 'east' is meaningful, there is.
I am not speaking as an idealist when I made the comment. To me, 'tomorrow' is just as real as 'one km east of here'. All of Einsteins theories presume the same, but it is admittedly a presumption. There are alternatives to his theories that don't make this presumption, but they came almost a century later.
It's fine to presume such things, but a topic about time travel seems to require that the 'destination' exists in order for you do deny your ability to get there. You can't argue that it can't be done because only the present exists, because there's no way to prove that opinion.
:ok:
Thanks for posting the video.
The problems associated with time travel cited in the video are as follows:
1. Time is not a physical object that can be moved or manipulated. It's simply a measurement of the progression of events.
2. The laws of physics, including the laws of thermodynamics, make it impossible to go back in time.
3. The idea of travelling back in time would violate the laws of causality, meaning that an effect cannot occur before its cause.
4. Time travel raises numerous paradoxes, such as the grandfather paradox, in which travelling back in time and changing a past event would alter the present and create a contradiction.
5. Even if time travel were possible, it would require immense energy and advanced technology beyond our current capabilities.
I have no issue with Point 1. I might add that time includes the progression of events, and is not merely its measurement, but this is not my concern here.
Points 2 and 5 make virtually the same point as each other. Point 2 says that time travel is impossible due to the laws of physics (however, it should be noted that this is only according to our current knowledge). Point 5 subsequently acknowledges the limitation of our current knowledge and technology and allows for the possibility of time travel.
Points 3 and 4 I believe are incorrect. This is what I was trying to point out with my earlier sketch of parallel timelines, which does not violate the laws of causality. I will attempt to develop this further below.
Imagine Bob was born in 1980. In 1990, at the age of 10, Bob has an idea for how to create the technology for time travel. Bob continues his studies and in 2024 he creates the technology which will allow him to time travel. Bob foresees the dangers of this technology, however, and realises that he must use his new time machine to go back and stop himself from ever creating it. Bob must kill his younger self.
Late in 2024, Bob enters his time machine for the first time and sets course for the year 1990. Bob arrives in 1990 and seeks out his younger self. He will probably be in school, Bob thinks. Bob finds his younger self, sneaks up behind him and takes his life as quickly and painlessly as possible. Old Bob is satisfied that his younger self will now never grow up to create the time machine and humanity can continue on more peacefully (at least for a little longer) without it. Bob is never discovered to be the murderer of his younger self and lives out the rest of his life quietly, until he dies in a fatal car accident in 2008.
Given that Bob has somehow worked out the technology for time travel and assuming that time travel technology or time travel itself does not somehow violate the laws of causality, what other laws of causality have been violated in this scenario? Bob is born, invents a time machine in 2024, travels to 1990, kills his younger self, and then old Bob dies in 2008. That is one event after another of cause and effect. Unless one can specify how time travel or its technology violates the laws of causality, then I don't see how else they have been violated.
As for Point 4, there is no contradiction. According to the standard "paradox", there is only a single timeline. Given a single timeline in this scenario, old Bob first arrives in 1990 to kill his younger self. Since he was murdered, young Bob cannot grow up to become old Bob, so he cannot build his time machine, so he cannot travel back in time to kill his younger self. Therefore, Bob could not have travelled back in time to appear in 1990. Hence, a contradiction. Or, per the grandfather paradox, if Bob were to travel back in time and kill his grandfather, then one of his parents could not have been born and then neither could Bob. Hence, a contradiction.
However, I will argue, there must be two (or more) parallel timelines in order for time travel to make sense. The timelines branch off into two or more timelines following the first time travel event. Let's call them timeline A and timeline B. Timeline B differs from timeline A only by the addition of the time traveller (and all that causally follows).
On the original timeline (A):
1980(A) - Bob(A) is born
1990(A) - Bob(A) has the inspirational idea for time travel technology
2024(A) - Bob(A) builds his time machine and travels to 1990
2025(A) onwards - the world continues on its course of the original timeline (A)
On the second timeline (B):
1990(B) - Bob(B) arrives in his time machine. This timeline differs from the original timeline only due to the fact that it now includes a time traveller, Bob(B). Bob(B) murders Bob(A) and then lives out the rest of his life on the second timeline.
1991(B) onwards - the world continues on its course of the second timeline (B)
2008(B) - Bob(B) meets his unforunate demise in a car accident
However far-fetched this may seem, it does not violate causality and leads to no apparent contradictions.
Maintaining the assumption that there can only be one timeline leads to the contradictions and violations of the laws of causality. If one dispenses with this assumption, then time travel is logical and causal.
The original timeline is required because the time machine needs to be invented in 2024 before Bob can appear in 1990. There must be a first, original 1990 in which no time travel event takes place before Bob can time travel back to 1990 (from 2024).
You are welcome.
Quoting Luke
Sure. If you say, you are allowing the parallel timelines running in possible worlds, then the argument becomes logically tenable. But one might still demand to prove the existence of the parallel time lines, before progressing further.
Quoting Luke It doesn't lead to apparent contradictions, but it doesn't make it true claims either. :)
One might equally demand to prove the existence of a single timeline before progressing further. I don’t see how this might work either way. I’m merely showing that time travel is hypothetically possible with a way to avoid the contradictions of the grandfather paradox and violations of the laws of causality.
From my own perspective, time doesn't exist. It is a mental concept. There is only "Now", no past and no future. What you call the past is your memory of the past now, and what you call future is your imagination.
Therefore I don't need to prove a single timeline or indeed anything at all. I would say, there is no such a thing as time. If you don't agree, prove that time exist, prove the past and future exist. If you cannot prove them, then all your points were just imagination. This would be my points to you. :D
This seems inconsistent with the video you posted which describes time as “a measurement of the progression of events”. You appear to deny that there is any progression of events. Nevertheless, I have little interest in trying to convince you otherwise, but I wonder how you account for the fact that we are all aging and that children become adults? Is that all in your mind?
Of course there are changes in the physical world and bodies. But that is not time. Time is measured quantities. There are durations and intervals, which is different from time. The claim that time is a mental concept, doesn't mean there is no physical and bodily changes.
Time is a conceptual product which is a mental product from observing the changes and intervals in the physical world such as the rising Sun every morning, the movement of stars, change of the seasons ... etc etc. It is not some physical entity.
You say year 2024 1990 ... but this is just some contingent contract of the human civilisations. It doesn't exist in the real world. It could be year 0 tomorrow if we all agreed.
Year AD1 was the year Christ was born. Do you believe in Christ's life? If not, then Year AD1 could have been any number. No one knows what year it should have been. We have no such thing as Time. It is an illusion.
Quoting Luke
And another thing, forgot to add. Your concluding claims are all in "If" form. They are not propositions. They are hypothesises and conjectures themselves in "If~" form.
Your concluding statements would only be true, if and only if you proved the "If~" parts as Truths which complies with the objective facts. So far, I don't see any evidence or proof for your "If" statements having been proved either True or False, therefore they remain as groundless conjectures.
This is true, and a serious problem for discussions of time as currently being explored.
But this doesn't mean 'time doesn't exist'. It means are symbols for it are arbitrary. I'm not trying to say it does or doesn't exist - just that this doesn't go to that question i don't think.
It may be that it's actually the year 14,564,335,235 AT (all time).
The video author seems also to presume presentism, implying that time itself would have to be re-wound (and the entire universe with it) in order to 'go back', rather than time being left alone and just the traveler going somewhere.
In non-presentist terms, it would require a discontinuous, or non-timelike worldline. Well, the worldline is just an abstraction, so it being discontinuous is not in itself a problem Several people have proposed valid methods to do (forward) time travel utilizing discontinuous worldlines.
Anyway, I have a problem with number 1.
Not at all. But it presumes a self-contradictory version of dual-presentism, that the universe causality is made to go backwards (less entropy) but real time continues to go forwards.
Fact is, my abrupt appearance in 1955 would not violate entropy laws at all, nor would it violate thermodynamic law. It makes a hash of causality, but that's not brought up in this point.
This one has teeth, but is worded wrong. Causality doesn't say an effect cannot occur before its cause, it says that the effect (information travel) cannot occur outside the future light cone of the cause. The future light cone is physical and objective (not frame dependent). The plane of simultaneity (referenced by the word 'before') is frame dependent and an abstraction, at least it is under Einstein's theory. It isn't under presentism of course, so that assumption yet again.
Anyway, yes, backwards (not forwards) time travel would violate causality laws, if they're valid laws.
Closed time loops are allowed under relativity, but like several other things, that doesn't mean there are any at a classical scale. Time travel isn't itself paradoxical.
Also, what did grandfather ever do to deserve this abuse? If you want to illustrate the paradox, go back 5 seconds and kill yourself, or otherwise disable the machine, which would probably happen anyway with a 2nd machine materializing right in the same place.
5. Even if time travel were possible, it would require immense energy and advanced technology beyond our current capabilities.[/quote]This is nonsense. 'If impossible thing, then [arbitrary unfalsifiable conclusion]'. The energy requirements are meaningless unless a method to do it is proposed.
Mostly point 3 that actually says that, seemingly the only point that isn't straight up unbacked conjecture.
A nit: He has to set his course for an event, which has 4 coordinates, not just one. Pretty much all the fiction (except xkcd) seems to forget that. Everything moves, but it is always assumed that the machine will reappear at the same map-location as it left despite the motion of stars, planets, etc. OK, Dr Who doesn't work that way. It's a car, and it travels in space as much as time.
OK, the 'spawn a new timeline' explanation. Yes, that avoids the grandfather thing, but doesn't resolve the physics violation of the machine in the first place, in particular, what caused the 1990 state with two Bob's in it.
And apparently Bob fails in his effort to destroy the bad thing resulting from his technology.
Um, that's a blatant violation. 'Old Bob' in 1990 is not the result of an antecedent state. If 2024 is the antecedent state, then the rest of this new timeline is not the result of that other antecedent state.
Thanks, but it would be a stretch to call it a summary. I just transcribed most of the very short video.
Quoting noAxioms
I propose that we avoid bringing presentism and eternalism into the discussion, that we simply assume time travel is possible and see what the consequences are for causality and contradiction.
As you may recall from previous discussions on time, my ontology of time involves a blend of presentism and eternalism (in short, that without presentism there is no 'progression of events', and without eternalism there is no timeline(s) of events). If eternalism solves a problem for time travel, that's great.
Quoting noAxioms
Right, given our current knowledge and technology. But let's assume that time travel is possible and see whether we can avoid a paradox.
Quoting noAxioms
Oh, then we are in agreement and I've wasted my keystrokes. I thought the grandfather paradox indicated that time travel itself is paradoxical?
Quoting noAxioms
Bob's time machine is the cause of the 1990 state with two Bobs in it. But if you want to know how a time machine works, I have no idea.
Quoting noAxioms
Not with the spawning of a new, second timeline (once old Bob time travels back from 2024).
Quoting noAxioms
Isn't this simply denying the possibility of time travel because of, well, time travel? The antecedent state would be old Bob's time machine transporting him from 2024 to 1990 (that is, 1990 on the new timeline, which now includes old Bob. Note that 1990 on the original timeline does not include old Bob).
Only one of these two statements is "in "if" form".
Anyhow, do you deny that Kant was alive in 1776?
Time exists, but not in the way the would-be time travellers think. :D
Quoting AmadeusD
If you established your own country or created your own world, then you could run it with that, suppose.
They seemed to be the concluding statements from your arguments.
Quoting Luke
No I didn't deny anything about Kant or 1776. My point was that you need to prove your "If" statements are true to the objective facts, to make them into true statements.
Your arguments might be valid, sound and not contradictory in modal logical forms, but that doesn't mean that they are true in the actual world. Bear in mind that, whatever happens, they all happen in the actual world. Before the proofs, they just remain as your conjectures and another hypothesises, which are not adding much more to the OP question.
Fair enough.
Quoting Corvus
My point was more that if we counted from the Big Bang time might have some relevance beyond social time-keeping. If the year we're using is based on the very first change that ever occurred, its much more palatable, I think, to take it as 'something'.
Quoting Corvus
A physical clock measures something. Hard to deny the existence of something that can be measured.
You seem to get around this by defining time differently than, well than how physics defines it, which boils down to 'what a clock measures'. I agree that the coordinates we assign to time is pure abstraction.
Quoting LukeSaved me from typing it. Most of the thanks was for that.
Quoting Luke
How about a growing block model then? The past exists. You can go to it, but since it is 'the past', you cannot change it. So a new branch is created (MWI style, but with physics violations), very much like your Bob story. I think that would satisfy both of us. The video presumes (I think) one would have to recreate the entire past state of the universe, hence the excessive energy required.
Quoting Luke
Wasn't wasted. Your Bob example showed how that paradox can be easily avoided.
Another way is to scratch the parallel world and let Bob simply destroy his younger self, and the time machine appears in 1990 uncaused. It's going to do that anyway (in violation of physics), but we're supposed to be ignoring known physics for this exercise.
OK, I said it wasn't paradoxical, but it's still a violation of the physics that we're ignoring. If sending information outside of the cause's future light cone constitutes a paradox, then its still a paradox.
Quoting Luke
The old timeline still has the bad technology. It just doesn't have Bob anymore. If it's just Bob that's the problem, he could fix that quick without bothering to build the machine.
Quoting Luke
No, the antecedent state would be 1990 minus 1 second. That cannot produce an old-Bob.
Either that or he didn't actually go to 1990, but simply rearranged the entire state of the 2024 universe to correspond to what it looked like in 1990, which seemingly is what the video envisioned.
Physics doesn't allow a vehicle to just materialize from nothing. But I'm told to ignore this inconvenient problem. Hollywood depicts it frequently, and they can't be wrong, right?
I don't recall why but I never fully endorsed the growing block theory. However, let's leave those ontological theories aside for now. They will probably come up again later.
Quoting noAxioms
Doing that would not remove the paradox, unlike the parallel world scenario.
Quoting noAxioms
I don't follow why it would be a paradox, only that it might be a violation of the physics. However, we need to assume that time travel is possible for the sake of argument. The typical grandfather paradox scenario also assumes that time travel is possible.
Quoting noAxioms
In the scenario I sketched, Bob's motivation for wanting to kill his younger self - because he thought the technology was too dangerous - is something I only added for the sake of giving him a motive. The important factor, which is relevant to the paradox, is not that the old timeline has bad technology, but that young Bob is murdered by old Bob on the new timeline.
Quoting noAxioms
I disagree. What precedes old Bob's appearance in 1990 is the use of the time machine in 2024. That's how old Bob comes to be in 1990. You seem to keep wanting to deny the possibility that Bob can time travel.
Quoting noAxioms
If you don't allow for Bob to be able to time travel then we will be unable to discuss the grandfather paradox.
I heard that Japanese folks have their own time system counting from their monarch's coronation days. So they run their king's name and year 25 or 30 whatever, as their alternative year counting.
Not sure if there was anyone witnessing the Big Bang, and recorded the time and how it went through. Unless that is the case, many people would still take it as another mysticism.
In Chinese Lunar Calendar, it is still 2023 November or December at the moment. Their new year day would be sometime in February I think. The main point is, time is a civil contract.
Sure, I am not saying it is not allowed to have conjectures and hypothesis on time travel. My point was the claim that "If X, Y, Z, then time travel is possible." remains as a hypothesis until X, Y, Z had been proved as truths which complies to the objective facts in the actual world.
Quoting noAxioms
I am not sure what the physical clock measures. But if it did, and if it is not something which is non conceptual time, then I would imagine it couldn't be time itself at all. It must have measured some particles going through changes into some other entities similar to the Nuclear fission process, which is the duration of the process. Would it be time itself? I believe not.
It sounds like your machine doesn't travel at all then. It manufactures a new world in 2024 that looks like how things were in 1990. It's a new thing, a copy. The time is still 2024, but the calendar hung on the wall is set to 1990. Rather than going through the bother of putting a copy of old-Luke (and the machine) in this newly created world, it would save effort by just creating the world like it was but without young-Luke.
The original 2024 timeline marches on, without you and the machine if the universe-creation process involves the destruction of the machine and its occupant, and still with you if it doesn't involve that and only places a copy of you and it in the new world created.
Anyway, if you hand-wave away all the physical reasons why this cannot be done, I have no problem envisioning time-travel scenarios that are free of paradoxes.
Quoting Corvus
We did. It's not like it happened a finite distance away and the view of the bang has already passed us by. Of course the really early events are obscured by the opaque conditions back then. The window through which we look took a third of a million years or so to turn transparent. By that measure, nothing could 'see' the big bang since it was all obscured behind a blanket until then.
Quoting Corvus
Nothing ever gets proved. I can go to grandma's house if I have a car, and the weather is acceptable, and if I draw breath. But technically I cannot prove any of those.
Point is, requiring 'proof' is going to far. Evidence of X,Y Z is probably enough for plausible time travel. Right now, that evidence is very negative.
Quoting Corvus
It measures proper time, which is very defined in both interpretations of time. It doesn't measure the advancement of the present, or the rate of the flow of time. That sort of time is more abstract, and there is no empirical way to detect it, let alone measure it. So maybe we're talking past each other when I reference the sort of time that clocks measure, vs you referencing the latter.
Could you explain why it must be a "new thing, a copy" of 1990 recreated in 2024 and why Old Bob cannot actually travel back to 1990?
It seems logical to me: Old Bob cannot time travel back to 1990 until he has built the time machine, and he does not build the time machine until 2024. This entails that there is a 1990 (on the original timeline) in which Old Bob did not appear and in which only Young Bob exists. It is not until 2024 (on the original timeline) that Bob first builds the time machine and uses it to travel back to 1990. It is only after this time travel event in 2024 that both Young Bob and Old Bob appear in 1990 together.
It seems like you're saying that my depiction of 1990 (on the second timeline) is incorrect because the real 1990 must always contain both Bobs, but you would need to explain the logic of that scenario. How do you account for the fact that both Bobs appear in 1990 prior to Old Bob's invention of his time machine? Does Old Bob still go on to invent his time machine in 2024? If he always appears in 1990, it seems unnecessary for him to build or use a time machine in 2024, so where is the time travel here? Maybe the original timeline gets "written over" (or "saved over") after the time travel event?
These sorts of contradictions and causal violations do not exist in the parallel worlds case.
If time travel is not using a time machine to travel back and insert yourself into an earlier time (at your time travelling age), even to perhaps a time before your birth, then I don't know what time travel is.
No I can't. You won't let me discuss interpretations at all. You said you're creating a new world, not altering the original, in effort to avoid the paradox. That means an act of creation of a new world.
You said that 2024 is the antecedent state, so that means the alternate (copy) 1990 state was created at that time. It's all I have to work with. I see why the video says it needs a lot of energy.
The original 1990 doesn't exist anymore. You can't travel to somewhere that doesn't exist. You have to create it, a copy of it. I'm running with that assumption when trying to understand what you're suggesting.
There's no contradictions with it because killing the copy young-Bob isn't killing old-Bob's actual ancestor.
I would think, yes, but I think there's more to it. On this view, that 'copy' only began in 1990. It could be reversed to 1990, but no earlier. The original time-line could be reversed to Bob's birth. I'm sure this means something, but I can't grasp what. But, it certainly seems, prima facie, that the time machine in fact replicates the chosen moment (but it is 'real' as such) and then that moment runs forward as-if it were an alternate time-line.
I have never said this.
Logically, it is necessary for Bob to build and use the time machine in 2024 before he time travels to 1990. This is not creating a new world, it is altering the original. It's Old Bob time travelling to 1990 from 2024. There is no point or possibility for Old Bob to time travel to 1990 if he is always at 1990.
And, on your view, there is no "original" 1990 to alter.
Quoting noAxioms
Of course. If time travel is to make any sense then the time traveller can't always have been at the time travel destination, otherwise there is no point or possibility of time travel.
Quoting noAxioms
That's not my position. I claim that both timelines exist in parallel, pre- and post-time travel, each with different histories following the insertion of the time traveller into 1990.
Quoting noAxioms
You also can't travel to a destination if you are already at that destination. Incidentally, 1990 does exist and it's Old Bob's time travel destination. It is only after he time travels to 1990, inserting himself into a time that he wasn't before, that the two timelines diverge.
Quoting noAxioms
You can call it a "copy" if you like. There are two parallel timelines, after all: one timeline in which Young Bob grows up to build a time machine in 2024 and another in which Young Bob gets killed by Old Bob. However, what supposedly happens to Old Bob in your single timeline scenario after he murders Young Bob? He just vanishes into thin air?
This would be the only realistic result, but then it would follow that this means he was never able to come back to kill Young Bob.
So we're still stuck with the 'copy' idea.
Quoting Luke
That says a parallel timeline [world] is needed, created since it doesn't otherwise exist. The 2nd sentence implies the 1990 new timeline branches off the 2024 'travel' event, which means no actual travel, just a universe creation event at 2024.
You say this, but perhaps worded it poorly and meant actual travel to an actually existing 1990, so it isn't something (a whole universe) that you need to manufacture.
Quoting Luke
OK, you acknowledge that the concept of a timeline implies the lack of presentism. There is no need for a 'progression of events'. Time travel under eternalism simply involves a worldline that is discontinuous, or doesn't follow a timelike path. So we ditch the presentism altogether, and that gives us a 1990 destination which we select as our target.
Now we do some retro-causality magic and branch a new timeline off of that point, which doesn't alter the original line at all except for Bob's abrupt disappearance from 2024, a violation of a bunch of conservation laws that we are ignoring. How is this Bob in the new timeline the same Bob as the old timeline? I mean, with the usual parallel timelines (MWI here), the Luke in some other world is not you, but somebody else.
Quoting LukeSounds like a copy to me. Old Bob is a continuation of the not-murdered original young Bob, not the Bob that gets murdered.
I don't have a single-timeline scenario. Heck, I don't have a scenario at all. Just trying to figure yours out. I've changed my guess significantly based on what you've said and based on some past comments that I read again. Is it better now?
What was our point here? If we can do this impossible thing, no contradiction need exist (except for the magic in doing it). I've long since expressed that the branching solution resolves the grandfather paradox.
Quoting AmadeusD
Sort of like Marty (or his picture of his older siblings) beginning to fade as he slowly destroys any possibility of his parents hooking up. Hollywood loves this idea despite the paradox it creates.
It does exist. It's the same 1990 that was there before (on the original timeline), except that before it did not contain any time travelling Bob. The only difference is that now it does contain a time travelling Bob, because Bob has just time travelled back from 2024 to 1990.
Quoting noAxioms
I wouldn't consider it time travel if a new 1990 must be invented at/in 2024. I consider that Bob's time machine actually works and transports him back to 1990 from 2024. He can't already be in 1990 (at his 2024 age, as Old Bob) without having time travelled.
The 1990 new timeline does branch off the 2024 travel event, but it creates a new timeline - following the 2024 travel event - which begins at 1990, in which Old Bob has now time travelled back and inserted himself into 1990. He wasn't at 1990 on the original timeline (as Old Bob) because he had not yet built the time machine. Everything else is exactly the same as it was in 1990 upon Old Bob's arrival, except that now it includes Old Bob. Isn't that just what we usually mean by time travel? If I wanted to travel back in time to kill Hitler, presumably I'm not already there/then.
Quoting noAxioms
Because he was Young Bob on the original timeline and then he grew up (into Old Bob) to build the time machine and used it to time travel back to 1990 on the new timeline to kill Young Bob. It's a logical sequence of events: Young Bob grows into Old Bob who time travels back to 1990 and kills his younger self. Old Bob continues living after this, and Young Bob no longer continues on to build a time machine. That's how the new timeline differs from the old timeline, which is a result of Old Bob's time travel and subsequent actions.
They are different timelines, but they started out the same way, and it's the same Young Bob in both up until the arrival of Old Bob from the future, which is when the two timelines diverge. However, the original timeline must precede the new, second timeline. Bob can't time travel or return to the past before he has built the time machine.
Quoting noAxioms
Right, Old Bob is not the Bob that gets murdered, because Old Bob is the murderer of Young Bob. You could say that Old Bob only murders a copy of Young Bob on the new timeline and that he does not murder the original Young Bob. However, murdering the original Young Bob is not possible according to the logic of the scenario, because the time machine needs to be built before Old Bob can travel to the past in order to kill Young Bob. Bob effectively changes the past from what it was on the original timeline (from 1990 onwards), which was his intent.
Quoting noAxioms
Sorry, I just assumed this from past discussions, since I thought you were firmly on the side of eternalism.
Quoting noAxioms
Yes, thanks for taking the time.
Quoting noAxioms
I assume by "branching solution" you mean something similar to what I've described here. Otherwise, I'm not sure what that means.
I only just found out yesterday that the idea of parallel worlds is not a new idea as a solution to the grandfather paradox.
I don't recall seeing it at all. Or anyone who claims to have witnessed the Big Bang.
Could it happen again? Or is it still happening the now?
Quoting noAxioms
There is a difference, when you are just keep talking to yourself making the "If" statements to yourself, and when you actually make philosophical propositions in public claiming that it is true or at least valid and sound.
Your interlocutors will request to prove your statements, if they sound unclear, invalid and unsound, so they can be rejected. Philosophical debates are about proving and disproving claims and statements as true, false or neither. And a statement cannot be both true and false. That wound be a contradiction.
The point is that unless it is your monologue or a pub talk, philosophical statements need to be proved and verified when not clear. If not, it could transform to a drama or comedy.
Quoting noAxioms
It sounds like we are talking about different time here. What is "proper time" and "interpretation of time"?
Agreed, more or less.
Having given this some further consideration, although some may find it unsatisfactory that Bob does not kill himself on the original timeline, I believe that the "branching solution" or multiple timelines view of time travel is the only way any sense can be made of time travel; and it is the meaning of time travel portrayed in most fictional accounts (AFAIK).
It should be noted that the singular timeline view of time travel, such as that depicted in the Grandfather paradox, does not permit the time traveller to kill themselves on the original timeline, either, because this is what produces paradoxical results. The time traveller cannot visit an earlier time on the original timeline without falling into contradiction, because there was either no time traveller at the destination time "the first time around" or because, otherwise, the time traveller was always at the destination time (i.e. the first time around) and time travel is therefore impossible (or, at least, unnecessary). The desire to time travel in order to alter the history of the original timeline that leads to the point at which the time traveller departs in their time machine is therefore futile on a singular timeline view. The time traveller was either never at the destination time and cannot return there without contradiction (having two conflicting histories on a single timeline), or else they were always there and therefore cannot "return" there.
On the multiple timeline view, although Bob creates a second timeline as a result of his time travel, at least from his perspective, it is possible for him to return to the past to do whatever he likes, including killing his younger self. Moreover, for time travel to make any sense, Bob must travel to, and insert himself into, a past time at which he didn't always already exist as a time traveller.
I believe the multiple timeline view is what is usually understood to be time travel and is the only way time travel makes any sense. Understandably, however, it may not satisfy those who want to alter the original timeline or murder any of its past inhabitants.
One can pretty easily do it just by having a space ship that travels faster than light, and fiction is full of that as well.
Why this restriction? I go back to 1955 (standard destination). Hang around until 1970, and go back to 1960 this time, where "I" already am as a time traveler. What's wrong with that? Can he also make a 3rd branch off the original timeline? Can I, having just made the machine, branch a new line off some other timeline where I never existed in the first place, say some version of 1980 where my parents didn't survive WWII?
Meanwhile, why do you want to kill anybody? The young-Luke you find back there is not you since 'you' is presumably on the original timeline. You've no reason to kill this other person or for that matter, anybody. If you kill yourself, have you killed Luke, or did a copy kill himself?
I think you need to consider the question I asked about the Studebaker in my first post in this thread (about post 57). Is that time travel? If not, why not? What is your machine doing that my example with the Studebaker did not?
:lol: I like your faith in humanity, Luke.
Quoting noAxioms
Surely, this is now talking about a "possible future" that you've gone in to - it may not be the actual future of your OG time-line. You being in the future isn't a contradiction here, though, as you're not in the OG timeframe. You just disappeared for a while in the OG one and reappeared at your 'destination' moment in time.
Then, the 'branch' would happen, I would suppose at a point in the OG timeframe that contradicted the future branch you've travelled to. This might create an alternate past, pro-actively (as far back as your moment of travel in the OG timeline) and I haven't considered if that's an issue. It seems unavoidable that there would be a branch, but not logically necessary. Very much happy to have this ripped apart though as i'ts taken me 10 minutes between settlements at work.
Quoting noAxioms
Surely this would just create a branch into which you've traveled regardless, leaving the OG timeline without you, or your parents, in it? A timeline into which you traveled and now exist rather than existing prior to the travel.
We "travel" to the past when we look at an old photo or watch an old TV show. That kind of technology might develop into a means of recording virtually everything in a particular sphere of activity, allowing those in the future to "travel" into the past without any paradoxes or violations of physical laws. In this sense time travel is dependent upon the present preparing for the future travelers.
If you think physical time travel to the past is possible, begin by explaining how.
According to the second clause, the time traveller always appears alongside their younger self in the past. The problem with this view is that the effects of time travel precede the causes of time travel. Given the normal temporal order of things from past to future, Bob appears in the past alongside his younger self in this scenario before he has built a time machine or time travelled. Therefore, there is no longer any need for Bob to continue on to build a time machine. We may ask where is the starting point of this causation chain? There exists a paradoxical temporal loop in which causes are effects and effects causes. Presumably, Bob built the time machine (in his later years) for the purpose of returning to the past, so did he forget that he was already in the past? Where do time traveller Bob's memories start and end in this scenario? If time traveller Bob is always in the past, then how can he return to the past via time travel?
The first clause presumes that time traveller Bob is not already in the past ("the first time around") before he has time travelled. However, if Bob were to subsequently time travel to the past, then this would create two different histories on the same timeline; one in which time traveller Bob is not in the past and another in which time traveller Bob is in the past.
Quoting noAxioms
I wouldn't call that time travel in the relevant sense. The SEP article attempts to draw the relevant distinction: https://plato.stanford.edu/entries/time-travel/#WhaTimTra
Quoting noAxioms
I think forward time travel is a bit trickier, but I suspect that it does also require a branch in timelines. I would prefer to consider the "simpler" backwards time travel for now.
Quoting noAxioms
My point was that it is senseless for Bob to travel to the past if he is already there (as is the case with a single eternalist timeline). I don't foresee issues with additional branching. I was only considering a singular time travel event.
Quoting noAxioms
I don't think so. I'm assuming that Bob returns to the same past that he lived through when he was younger. It's just that he cannot have been there as a time traveller the first time around, before he built his time machine.
Quoting noAxioms
I don't; that's the scenario of the Grandfather paradox. For example, see here: https://plato.stanford.edu/entries/time-travel/#GraPar
Quoting noAxioms
Call it a copy if you will but this is the only way that time travel is possible. It is not possible for Bob to return to the past on the original timeline due to the resulting violations of causality and contradictions. The second timeline differs from the original only in that there is no time traveller on the original timeline until after Bob has constructed and used his time machine. The only way for Bob to return to the past to meet his younger self is on a second timeline, so the only way for Bob to return to the past and kill his younger self is on a second timeline.
Quoting noAxioms
I assume that it is the Bob (or Luke) from the original timeline who time travels to the past and creates a second timeline in the process. Bob therefore remains on the original timeline until his time travel event when he relocates to the second timeline.
Quoting noAxioms
As I replied earlier, I wouldn't call this recreation of another time in the present time to be time travel. I am assuming that Bob's time machine actually works and transports him to a period of time other than the (present) time that we are currently living through together.
I read almost all of the SEP article. Thanks for the link. Didn't know it had a page on the subject.
Apparently what I am doing right now does count as time travel, so long as I move. Motion-related time dilation apparently counts according to the article. I would not have said that.
The definition they referenced (but were not totally satisfied with) came from Lewis (1976) who says that time travel is when two different kinds of time (coordinate time and proper time say) don't match. The clock on the wall says one thing, but my watch says another. But physics allows that sort of stuff all the time. One is always proper time, but the other is something else. The SEP article seems not to know physics enough to actually use the correct term of 'proper time', the length (interval) of any worldline, which is what a clock measures if it follows that worldline.
The article doesn't ever reference 'branching', but it talks about traveling to other parallel timelines, like those lines already existed, and apparently already have the time machine appearing from nothing in them, much to the surprise of any witnesses.
The article does seem to accept travel to a 'nonexistent' time in the past under presentism. All of section 4 discusses the various interpretations of time and their implications.
Quoting LukeHim already being there was the point: To alter what he (younger self) would have otherwise done. I see no reason why the younger self cannot have already time travelled before. Another mistake could be made, 'necessitating' a second correction. I put it in quotes because the mistake cannot be corrected on the more original (more real?) timeline.
Quoting Luke
Poor assumption. If I'm to 'kill grandfather', I'd have to go back at least a century. Maybe I want to witness the asteroid taking out the dinosaurs. You can't put in a rule that says you can only travel a short ways to some past with you in it somewhere.
You also contradict yourself. You say on one hand that it is senseless to go to a time when you exist, and on the other hand you're presuming Bob does this 'senseless' thing.
Quoting Luke
Any travel to the distant past will destroy the history you know. Everyone talks about critical events that make a change, but just appearing and stepping on a bug is enough. That said, killing grandpa isn't necessarily paradoxical. Maybe you're not actually related to him, but rather the mailman. I know my grandfather was a cheater. Why can't grandma be?
Quoting Luke
Well, besides the fact that it isn't possible in the first place, there are valid scenarios discussed in SEP that allow travel to the original timeline. CTCs are one example.
Quoting Luke
I don't make that assumption. I try to work it out.
Quoting Luke
I'm not recreating a time. I'm just moving a Studebaker forward in time by a century. That's pretty much exactly what you're describing, except in the forward direction. So tell me why that's not what I did. How do you back the assertion that the car didn't travel through time, but Bob (also going forward say) did. Was it the lack of a fancy time machine looking device with blinking lights and stuff? There's plenty of fictions where the machine isn't necessary.
They've done quantum teleportation, which counts as time travel according to SEP. They put something in a booth and it teleported it to another a couple hundred km away. Arguably not time travel, but my question is: Is the thing at the far booth (and no longer at the near one) the same object, or a perfect copy? They were asked this question, and replied: "What possible difference does it make?".
As long as you move at a relatively different speed to the rest of us, I suppose. Anyhow, that's not quite what you said earlier, which was that you are time travelling by staying on your own timeline. This could be achieved by something like 'waiting', which the SEP article categorises as not time travel.
Quoting noAxioms
I agree that the point of the time travel is for him to be at the earlier time in order to alter what he would have otherwise done. But this is what necessitates his time travel to the earlier time destination. There is no point or possibility of travelling to a destination if you are already there. That is my point.
Quoting noAxioms
The younger self does not time travel; the older self does. Old Bob travels back to the time when he was younger. In the context of the Grandfather paradox (or one of its variants), the purpose of the time travel is for Old Bob (the time traveller) to murder his younger self. The younger self has not yet grown up to build a time machine, so he cannot have already time travelled before. Obviously, there may be scenarios - unrelated to the Grandfather paradox - in which Young Bob jumps into Old Bob's time machine after he arrives and then Young Bob uses the time machine to time travel to another time, but I see no point in complicating matters further.
Quoting noAxioms
I haven't suggested that the original timeline is "more real" than others. However, you have suggested that the inhabitants of the second timeline are merely "copies".
Quoting noAxioms
I don't rule out that Bob can travel to some time before his birth. I was referring to the context of the (Grandfather paradox) scenario I've described, where Old Bob time travels in order to murder his younger self.
Quoting noAxioms
I'm saying time travel is senseless on a single timeline, and that it only makes sense if there is more than one timeline; where a second (or more) timeline is created as a result of the time travel event.
Quoting noAxioms
For the sake of argument, let's presume that he really is your grandfather. Then it would be paradoxical; at least, on a single timeline.
Quoting noAxioms
Again, I was speaking within the context and logic of the Grandfather paradox, which is presumably a 'doctor' or 'leap' type of time travel rather than the others described in the article. I wasn't really considering those other sorts of time travel scenarios.
Quoting noAxioms
You asked whether it was Old Bob or only a copy of Old Bob who killed his younger self. My answer was that it is Old Bob from the original timeline who time travels and kills his younger self (on the new timeline). When Old Bob time travels, he disappears from the original timeline (at his time of departure) and appears on the second timeline (at his time of arrival).
Quoting noAxioms
Going by your earlier description:
Quoting noAxioms
I've said that I'm not (or that Bob is not) recreating a past time (e.g. 1990) in the present, and that Bob actually time travels to 1990. You say that recreating the 1928 Studebaker now is not time travel and I say that recreating the year 1990 now is not time travel. If you were to recreate it today, then you haven't really moved a Studebaker forward in time by a century. As you note, "this isn't time travel being described". I thought we were on the same page here?
I don't think your timelines are parallel like the ones discussed in SEP. The question seems more approriate for the above mentioned authors.
Quoting LukeYou seem to regard them as copies yourself, as evidenced by several comments (my bold):
So by this wording, the young Bob that gets killed is not Bob. He is not already there, but is rather killing a copy, somebody else, having left the young Bob that is actually himself back in the original timeline unkilled.
If the two of them were the same person, this would be a direct contradiction. But you seem to regard them as not the same person. So if (actual) Bob goes to some parallel world in 1990, and waits several years for the perfect opportunity to take out the young-Bob copy1 that is there. The moment comes, and he fires his gun only to find it wasn't loaded. Opportunity lost, and there won't be another one. But he has a time machine, so he goes back a day and loads the gun that yesterday-Bob (also a copy) can use to complete his task (of killing young-Bob copy2, leaving young-Bob copy1 un-shot back in the first alternate timeline).
My point of all that is that your comment is true only if you assume yesterday-Bob is a copy. Yesterday-Bob (the one with the empty gun) has time traveled (he's the original Bob). Yesterday-Bob copy has not, him being a different person with a false memory of having time traveled. If he was the same person as Bob, then he very much as time traveled, explaining his presence in 1995 and his memory of 2024.
Quoting LukeAll the examples of 'is time travel' at the top of the SEP article are single-timeline examples. I'm not saying that traveling 'sideways' to a different line is or is not time travel, but I'm saying that those examples cannot all be senseless. Yes, they all have potential paradoxical consequences, all discussed in the article.
Quoting LukeMy reason for asking was to figure out justification of that assertion. I'm not saying it's wrong, just an arbitrary designation. Most designations of identity have pragmatic reasoning and are thus not arbitrary. This doesn't, so the question needs asking, and the answer needs justification.
You wanted to explore the implications. I'm trying to do that.
It did not exist before Bob travelled to it; the new timeline is created by Bob's time travel. It is the same as the original timeline, except now with the addition of a time traveller: Bob.
Quoting noAxioms
The new timeline did not exist before Bob arrived, so there was no "original" version of the new timeline to alter. The original version is the original timeline, from which Bob departs. The original timeline does not have a time traveller arriving in its 1990. 1990 on the original timeline contains only young Bob (sans time traveller) who grows up to be time-travelling Old Bob. It is only on the new timeline that young Bob meets time-travelling Old Bob; when Young Bob and Old Bob exist together at the same time. The new timeline is created when Bob travels from the future (of the original timeline). To illustrate:
Original timeline:
1990: Young Bob (only) who grows up to become Old Bob the time traveller
2024: Old Bob time travels to 1990 in order to kill Young Bob.
2024 (post-time travel): Bob is no longer on this (original) timeline from this time onwards.
New timeline:
1990: Old Bob arrives in 1990. The new timeline now contains Young Bob and Old Bob together at the same time (this is not the case on the original timeline). Old Bob kills Young Bob.
1990 (post Young Bob's murder): Old Bob lives out his life.
If Old Bob was at 1990 on the original timeline (i.e. on a single timeline), then the time travel event must have occurred before Bob built the time machine.
Quoting noAxioms
You can consider them to be copies, I suppose, but it's the only way I can make sense of the occurrence of time travel. It's not a copy of Old Bob, since he time travels from the original timeline to the new timeline. But the new timeline might be considered to contain a copy of everything/everyone else. Alternatively, the new timeline could be considered as how the (original) past gets changed by the presence of a time traveller from the future (following the time of their arrival). I believe that is what we should expect from a time travel event. If you are going to time travel back in time to kill Hitler as a baby, then Hitler can't have already been killed as a baby in the past. What's the point (or possibility) of time travelling to the past if it is to leave the past completely unchanged?
Quoting noAxioms
It is (Young) Bob that gets killed, but not (Young) Bob from the original timeline, that's true. Young Bob from the original timeline is the one that grows up to be Old Bob the time traveller/murderer. This is the only way to avoid contradictions, paradox and violations of causality.
Quoting noAxioms
I do regard them as the same person at different times, but the logic of time travel allows for an older version of a person to meet their younger self. That is the scenario of the Grandfather paradox.
Quoting noAxioms
You could consider them to be copies or you could consider it to be Bob actually changing the past from what it was originally. Obviously, Bob cannot change the past on the original timeline, because he was not in the past (as a time traveller) on the original timeline. If Bob were in the past (as a time traveller) on the original timeline, then his time travel would not change the past. In fact, in that case, Old Bob would be in the past before his time travel event (or without needing to time travel). It is only if Bob were not in the past (as a time traveller) on the original timeline that he could change the past from what it was (albeit on a new timeline) by the mere insertion of himself into the past as a time traveller.
Although Bob cannot change the past of the original timeline, he can create a new and different past to that of the original timeline, which I think is as much as can be expected while also avoiding paradox or contradiction. In order to change the past, the past needs to have been a particular way previously. Similarly, if I want to change my hair colour from brown to blue, I can't change the fact that it was brown originally.
Quoting noAxioms
Right, but I'm attempting to point out why I think single-timeline examples of time travel are senseless, and why I believe that a second timeline is necessary to avoid contradiction or paradox. However, I may have done a very poor job of that so far.
Quoting noAxioms
I am arguing that Old Bob cannot have been in the past originally, because Young Bob had not yet grown up to build a time machine or to time travel.
Quoting noAxioms
I appreciate it. Hopefully I've helped clarify my position a little better with this post.
I take it you're not a historian. Those guys would love a machine that lets them go back, even in a way that cannot alter anything, just watch.
I think we're doing considerable damage to causality if any of this were plausible. OK, the Einstein time travel doesn't violate causality, but I personally don't think that one counts even if it meets the SEP definition.
The SEP article gives several examples of a single timeline without paradox, Some of the best are the loop ones, including a case where you don't even need to invent/build the machine. You just give it to your younger self when you're done with it.
There is a sort of paradox with that scenario which is how the machine experiences no entropy: It stays perfectly new at all times, which isn't plausible for something that is thousands of years old.
Quoting Luke
You don't seem to understand my point, which is that there is not obvious convention as to if the old-Bob in the copy timeline is the same old-Bob from the original timeline. The usual conventions for saying this person is the same person that looked like him yesterday. "I bought a can of beans yesterday": True? By convention, yes, the person who bought the can of beans is the same person that submitted this post. We know that because we know the convention. There is no convention for crossing timelines. To me it looks like old-Bob commits suicide, but builds a copy of himself (and the machine) in a timeline with a copy of everything else. The convention could just as easily say that.
That could be, but the existence of Bob and his time machine ends on the original timeline with the time travel event. This does not happen to anything else on the original timeline.
Also, Bob has built the time machine with the intention of returning to the past, so he should not be surprised by his sudden appearance at an earlier time, unlike everyone else on the new timeline (who we would assume have never encountered a time traveller before).
Also, instead of considering the new timeline as a copy, you could consider it as a re-writing of history, but one which does not eliminate the original timeline.
Quoting noAxioms
Ah, but if they were to travel to the past then that would be altering something about the past; namely, that the historians were not originally in the past (as time travellers). Their additional existence in the past, even as mere spectators, would change the past. This is the most basic contradiction in relation to time travel on a single timeline.
Quoting noAxioms
It's not the sort of time travel I had in mind, either.
Incidentally, based on my very amateur understanding, I had thought that once the Einsteinian "time traveller" had returned to Earth, the same amount of time must have elapsed on Earth as it has for the traveller, given the time dilation effects of turning their ship around in order to return. When I read about the twin paradox long ago, I figured that although one twin can be in the future of the other, there is no way to transmit information to the Earthbound twin which could give them advanced knowledge about the future and that they must both return to the same proper time when they meet again. However, I admit that I don't fully understand these things and I'm probably way off. Besides, those sorts of time travel scenarios involving that type of "time travel" are not what I had in mind here.
Quoting noAxioms
There are three scenarios described in section 3.2 on causal loops. I reject them on the same basis as the arguments I have given here. I will respond to each of them below.
The scenario wants us to imagine that this is a logically-sealed causal loop. However, the time machine must have been built by someone else in order for it to have been stolen and then donated to the museum. It wasn't the time traveller that built it, so it cannot be the donation by the time traveller that causes the existence of the time machine.
The logical order of things is that:
(i) someone else built the time machine;
(ii) the time machine ends up in the museum (somehow other than via donation by the time traveller);
(iii) the time traveller steals the time machine from the museum;
(iv) the time traveller use the time machine to return to the past;
(v) the time traveller donates the time machine to the museum.
The causal loop (steps (iii)-(v)) begins only after the time travel event, but it cannot logically eliminate steps (i) and (ii). Logically, someone must have built the time machine to begin with; such things cannot "simply exist" uncaused. This is much like what I am suggesting with the original timeline of Bob. Young Bob first has to grow up through a period without time travellers in order to build the time machine and return to the past as Old Bob.
The time traveller must have possession of their time machine before the causal loop begins, in a way which does not rely on the causal loop. Otherwise, the time traveller cannot time travel in order to create the causal loop. If you don't have a time machine then you can't time travel, so you can't then obtain that time machine (that you don't have) via time travel (that you can't do).
The time travelling older self must have had this knowledge before the first time travel event, and must have obtained this knowledge in some way other than via the time travel event. Without the knowledge to begin with, they could not have time travelled and therefore could not have given this information to their younger self. They must have obtained this knowledge by some other means prior to first time travelling. This is another attempt to eliminate the start/cause of the causal loop.
I don't buy the fact that the time traveller could not have done something else. Their only constraint is the presumption of a single timeline in this scenario and the avoidance of contradiction.
Quoting noAxioms
I don't follow why it must be thousands of years old. I imagine the causal loop in these scenarios to be a much shorter period than thousands of years.
Quoting noAxioms
If we don't conventionally say that we are mere copies of ourselves in our normal passage through time from moment to moment, then I see no reason to apply a different convention to time travellers.
Any witnesses to Bob's first moment's on that timeline will be surprised by the apparent sudden appearance of Bob, despite the fact that he has been there all along and by definition doesn't appear somewhere where he wasn't just before. There simply isn't a 'just before' on that timeline.
That would be a different convention. The new timeline is a rewrote-history according to traveled-Bob, and the old timeline becomes the copy from which he originated.
There are stories/scenarios in which nothing is altered. It's more like watching the past on TV since nothing there can detect you.
The twin goes out and comes back, and the two twins are no longer the same age. Not sure what you've been reading, but the proper time going out and back is less than the proper time of a direct path between the two events where the depart and meet up again. None of this requires anything communicating or having knowledge of what the other is doing.
It works better with pregnant women, who make great clocks. Betty and Veronica both get knocked up the same day and Betty takes off for the stars. Betty comes back in 9 months her time and has her baby. She meets who she presumes to be Veronica also giving birth in the same hospital, but it turns out the woman is actually Veronica's daughter giving birth to Veronica's grandchild. 20 some years have passed on Earth since Betty left and the other woman is merely the spitting image of her mother.
Anyway, SEP considers that to be time travel.
Does not follow. That sort of reasoning is only valid if time travel is not possible. The whole point is that it was never built.
The existence is caused by its own time travel to the past. Such is the nature of closed loops. Still, in my prior post I pointed out a hole in that story.
That version works better since it mostly solves the problem I identified.
The closed-loop scenarios illustrate free will (or more precisely, the lack of it) better than any discussion about reality where there's no pragmatism to it.
There are several fiction stories with closed loops. Predestination is one of them.
It takes say 10 years from donation to museum to getting stolen. It ages 10 years during that time after which it goes back 10 years and does it again, and again... Infinite age since it's stuck in a loop. Somebody has to do one excellent refurbishment effort somewhere during each 10 years.
It's a loop. It has no finite length, just a period, just like there's no end to walking east.
I'm considering Bob to be the first ever time traveller. This is because I find the logic of single timelines and closed loops to be problematic at the first time travel event. Given that Bob creates the first time travel event, nobody has ever encountered a time traveller before.
Quoting noAxioms
I don't disagree with this, except for your insistence that we call it a copy. In a sense it is, but it is also the only way that time travel can work; the only way a time traveller can visit a past they've never visited before without causing a contradiction, If you change the past from being history A to being history B, then you can't eliminate the fact that it was history A before you made it history B..The different histories are the different timelines. Otherwise, on a single timeline, there would be a contradiction: the past both does and does not contain a time traveller.
Quoting noAxioms
Well, I wouldn't call that time travel or "travelling to the past", That is just somehow viewing the past at the present time of the viewers.
Quoting noAxioms
I understand the intended point of the example. You will need to explain why my objection does not follow. The "logical order of things" I described included time travel, so I don't see why my reasoning is valid only if time travel is not possible.
Quoting noAxioms
I understand that is the intended point of the scenario. However, I raised an objection to its logic, which was:
"If you don't have a time machine then you can't time travel, so you can't then obtain that time machine (or its technology) via time travel."
The examples provided rely on the time traveller having obtained their time machine or its technology via time travel before they ever had the means to time travel.
Since you can't time travel without a time machine, it cannot be a closed loop. The chain of causes cannot begin after the time travel event, because there can be no time travel without a time machine. Being in possession of a time machine must be the initial cause of everything that follows, so the initial possession of a time machine cannot be the effect of its time travel event.
Quoting noAxioms
Which hole are you referring to? Entropy?
Quoting noAxioms
The loop could have started only 10 years ago. Also, the advanced technology of a time machine could give it thousands of years of repair-free use, but I see your point.
You're not reading my comment. I said that by your rules, a person can be in the presence of at most one actual time traveler. We could have a factory that made them like bags of cheetos, and everybody used them to get to appointments and catch the traffic light that just went yellow. If they were used like that, the planet would quickly have a population of zero in not just the original, but all the timelines. Despite that prediction, no person would ever be in the presence of more than one actual time traveler, which is the one and only person that created the specific timeline the person finds himself in (if he's still in it and hasn't left already).
Actually, nobody would use the machines, due to the overwhelming evidence of it being nothing more than a self-annihilation machine. So good thing Bob is the only person that has one, and only Bob fails to exist in pretty much any of the timelines.
But the way you describe it, it isn't really the past, just a different timeline which maybe looks like 'the' past, but is actually just another line, 'a' past at best, one of many. There is only one 'the' past, and you didn't go there.
Except he can't leave (turn off the TV so to speak). OK, I agree that it stretches the definition too much. But if he's there at all, history is gone. If I go back 250 million years to see the early evolution of mammals, I'm sorry, but humans will never evolve from that timeline. Your very presence destroys that, although it doesn't prevent the asteroid that wipes out whatever is there instead of the dinosaurs.
[quote=Luke]the time machine must have been built by someone else in order for it to have been stolen and then donated to the museum.[/quote]
[quote=noAxioms]Does not follow. That sort of reasoning is only valid if time travel is not possible. The whole point is that it was never built.[/quote]
Try to state the logic of your statement formally. What are the premises? How does your conclusion (that the closed-loop machine must have been built) follow? One of your premises is perhaps that all things need creating at some point, but that premise begs a universe with no closed time curves.
I accept that premise, at least for purposes of this issue.
Why not? It works, does it not? This is worded as a conclusion, not an additional premise. I don't accept it since 1) it doesn't follow from the premise, and 2) it is easily falsified by counterexample.
Again, try to word it more formally, and the errors will stand out better. I think the example of learning the technology from the future works better than actually being handed the machine.
The one we discussed: the machine needing to exist for infinite time without showing any wear. Hence better to be handed the plans than to be handed the machine. The movie predestination works that way. It depicts a closed loop, without the infinite-age issue.
It wouldn't be a loop if it had. Loops don't have a start.
Unless more than one person used the same time machine to time travel together. I don't understand why the planet would quickly have a population of zero in all timelines though.
Quoting noAxioms
Bob would continue to exist on any timeline he travelled to (at least, until he dies).
Quoting noAxioms
Right, but it would be logically impossible to travel to 'the past' (i.e. on a single timeline) unless I was somehow already there before I time travelled. But how could I already be there before I time travel?
Quoting noAxioms
How?
Quoting noAxioms
Maybe it all boils down to this. I'm arguing that causal loops require a start; that there must be an initial time travel event which causes the loop in the first place, and that what causes the initial time travel event and subsequent causal loop cannot be an effect of that initial time travel event. I don't believe that a time machine can just magically exist uncaused.
Quoting noAxioms
I've been trying to state my premises. I will try again to be more clear.
My premises would be that:
- one cannot time travel without a time machine
- time machines need creating at some point
- there must be an initial time travel event following the creation of the time machine, when the time machine is first used to time travel
- the initial time travel event cannot cause itself (e.g. by a prior time travel event using the newly-invented time machine).
“ As always, these are vague, young, naive ideas I’m having. I’m not trained or anything yet”
I think this is as close as it gets, and I’ve been struck by somewhat of a structural analogy that may further the idea.
Wittgenstein in his missing years watched movies constantly, anything on the screen. He was said to be autistic. At least on the continuum.
In the movies, the rate of projecting stills into movement, I believe has a correlation to receiving signal which represent the frames, or bound content at which the signal projected on the screen can simulate the reality that expresses normal, everyday movement.Too fast a rate shows that as less real a representation, as too slow as well.
As the rate of projection nears the unrecognizable blur of the continuum, the frames , begin to loose their distinct stillness of separable framings of reference,
What happens then is that spatial perimeters elongate and trick the rate of eyeball incoming signals and the signaled neurons interpret this as a spatial increase, while duration as represented appears to increase
.Wittgensteins understanding was difficult to interpret because his metaphysical perception , of qualifying a Kantian-categorical sense of boundedness, could
visually only recognize it’s quantitative sequencing ,as the unreality of rates of projection could relate only to absolutely framed referenced signals without motion to the non objective look of the stop content .There must have been that, which excluded the range considered as near real representation.
This too, is a naively real formulation of what goes on within the semblance of minds occupied with ideas such as looking back toward a journey to the back.
well, if everybody had one and knew it worked, I suppose they'd all use it and exit any particular timeline. It's sort of like heaven: The sales pitch is great, but if it's such a better place, why does nobody voluntarily hit the button and go there? It's because from the perspective of the original timeline, it just looks like you vanish, never to be seen again. There is zero evidence that it is safe, let alone works.
And Bob is missing from every timeline except one. Of course on the other timelines, there may be many people that attest to having traveled, and the evidence is there that it works. Those timelines would empty out faster than the original, if only from people going back to times when there were still people to meet.
Nobody on these worlds knows who the actual time traveler is (the one that created this world), not even Bob.
With a time machine of course. That sort of logic only holds water because there are no time machines possible.
Evolution is a chaotic function. The popular term for it is 'butterfly effect'. The killer asteroid is not chaotic, so you don't alter that, but evolution is a random process, and you've totally altered that. People are not an inevitable result of the state of 250 million years ago. It's an inexpressibly low chance even without the traveler mucking things up. OK, that last statement presumes a lack of hard determinism. Our discussion has a lot of quantum interpretation implications as well as implications for interpretation of time. The SEP article didn't mention the former.
No. The whole point of them is that they are uncaused. They'd not be a loop if they were caused. That it doesn't fit in with your notion of singular causality is irrelevant since all those rules must be discarded with reverse causality.
I added bold labels. Let me know if I did it wrong.
P1: I said I would accept this for this purpose, but there is no such requirement. If time travel was possible, somebody might be able to do it just by willing it. If a machine can do it, why can't a creature evolve a way to do it. The premise is something like saying you cannot get to grandma's house without a car. Well, that's false since evolution has given us a means of machineless locomotion.
P2 is unacceptable. It's like trying to prove God by asserting that the universe needs creating at some point (which is itself a self-refuting argument). An un-created time machine does not violate any rules in a universe where time travel is possible.
The argument falls apart there: an unacceptable premise, which again, has a counterexample which falsifies it.
P3 seems false. I might make a time machine but never use it. We presume you mean the machine in the loop, so yes, it just happens to get used (the 'first time' say) in the story you are creating. I put 'first time' in scare quotes because there can't be a first time in a loop: there cannot be an odometer on the machine that records how many jumps it has taken.
P4 is OK, but seemingly irrelevant since your story involves only a single time travel event, no loop at all.
I listed them all as postulates (and no conclusions) since none are worded as conclusions. I don't see any conclusion of the impossibility of a closed loop. The whole things doesn't seem to discuss loops at all. It discusses only a created time machine, not a looping one.
In that case everyone would remain on the same timeline, so it does not follow that every timeline would quickly have a population of zero.
Quoting noAxioms
This still doesn't explain how every timeline would quickly have a population of zero.
Quoting noAxioms
What I meant was: how could I already be in the past before I have ever time travelled? I could already be in the past (on a single timeline) if I had time travelled before but, given causality, there must have been a first time that I ever used the time machine to time travel. How could I already be in the past prior to that?
Quoting noAxioms
Why are no time machines possible? That's not something I've said.
Quoting noAxioms
We can just discard causality and assume that time machines don't need to have had a first ever use, and we can conveniently disregard whatever history led up to that first ever use?
Quoting noAxioms
That's fine, but if a creature evolved a way to do it, then there must have been a first time that they ever time travelled. Evolution actually works in favour of my argument because it cannot disregard the history that precedes the first ever time travel event.
Quoting noAxioms
If you accept that one cannot travel without a time machine (P1) - at least, for the sake of argument - then it follows that a time machine (or the means for time travel) must be created or have evolved or somehow brought into existence in some manner. This is not trying to prove God in order to prove the existence of the universe; it's merely assuming the universe must have been brought into existence (which is quite self-evident). Hopefuly we can agree to the standard scientific view that the universe's existence began with the big bang, but even if we might assume that the universe has always existed, this is not very much like a time machine. To say that time machines have always existed is more like saying that waffle irons have always existed.
Quoting noAxioms
Sure, but it would imply no time travel.
Quoting noAxioms
Why can't there be a first time in a loop? Loops are immune to causality?
Quoting noAxioms
It's not irrelevant. I'm saying that if a loop involves time travel (as the examples in the SEP article do), then we can consider the first ever time travel event in that loop and what preceded it. Unless you are arguing that there is no causality in a loop or that time travel loops and time machines in loops have always existed? Why should causal loops be immune from causality; from having been caused? It seems like a bit of magic.
The people on the alternate timelines would have solid evidence of it working. A car gets caught by a train crossing, so it goes back 1 minute in time and sneaks across the tracks before the gates come down. The traveler can see her own car doing it as she approaches, and the bystanders can witness it as well. The person doesn't always reappear. Sometimes the traveler is gone forever. Kind of pot luck, a game of Russian roulette.
If you time travel to the past, by definition you end up somewhere 'before' the event where you initiated the travel. I kind of lost track of the context. Are we talking about the loop here?
I don't see how that follows with the loop scenario. There would be no 'first time' to a loop. As I said, there can be no odometer on the machine counting jumps. That would be a contradiction.
If it's just teaching the younger-self how to do it, then every jump is the only jump, so I guess that would count as the first (and only) time, or at least the one jump that defines the simple loop.
I don't understand this. If the jump is from 2024 to 1990, then 1990 is 'the past' destination, and you are not in a past that is prior to that except perhaps as a young person, the one that you teach.
We're presuming they're possible, hence the logic you give being fallacious. Things that are impossible in this universe are not impossible in this alternate universe where time travel makes for different causal rules. A loop is valid under the new rules. It doesn't violate anything except the rules of this universe.
You need to discard the causality rules of this universe, yes. The rules are different in the universe we're discussing. With the loop scenario, there is no 'first ever' to it. You can't count them. The loop is just there, and is self-consistent.
Not if it is part of a loop. The whole 'must be a first time for everything' is only a rule in a universe like ours, intuitive to us, but not true in the sort of scenario we're discussing. Yet again, a simple counterexample falsifies your assertion. So maybe this time traveling creature never evolved, but just is. Again, there are movies depicting pretty much this.
P2 is unacceptable. It's like trying to prove God by asserting that the universe needs creating at some point (which is itself a self-refuting argument). An un-created time machine does not violate any rules in a universe where time travel is possible.
— noAxioms
I will not. We're discussing the possibility of closed loops, and loops falsify P2.
I don't find that evident at all. It violates Einstein's theories for starters, which suggests that time is part of the universe, and not something in which the universe is contained and in need of being created.
Pop science view maybe. OK, if one confines one's definition of 'the universe' to just what evolved from the big bang, then a good deal of them would suggest a larger structure from which that bang was initiated. But there is no before/after without the sort of time that boiled out of the bang, so calling it 'before' is misleading.
If you consider the universe to be the entire quantum structure, which includes all the stuff that 'springs' from it, our bang being one of them, then that structure is not something 'created' or 'caused'. It cannot be, both terms implying a larger container for something we're defining to be the largest container.
Sorry to be so buggy, but I don't buy that either. The phrase once again implies a universe contained by time, and not the other way around. Yes, there are those that suggest something like that, in denial of Einstein's postulates.
Your wording suggests that the machine exists at all times, which isn't the case. It exists in the loop in the museum case. It doesn't exist at other times.
In the teaching case, it is built by young Bob in say 2022 with knowledge from his older self. Bob can then use to travel all over the place, here and there, to say the restaurant at the end of the universe. Eventually he goes to 1990 and teaches his younger self the secrets. Then he's off again to see even more wonders. Point is, there no point in time where that machine cannot be unless it has a limited range or something.
Same counterexample falsifies this.
Imagine you're holding one of those party poppers that you pull and it explodes a bit of confetti around. You're about to do it and a box appears in front of you from which a some guy jumps out and explodes his own party popper as he says "three!". Then he grabs yours (unpopped), and apologizes, says the box is a time machine that goes back 8 seconds, the says "One, two, ..." and the box disappears, leaving you simply befuddled. That's what an 8 second loop looks like.
It's not too hard to take that one apart, but not by the logic you've been attempting.
The kind of causality rules you're thinking of don't exist in a universe with time travel. A first time for a loop would contradict its existence, which is travel from the other end of the loop and not somewhere else.
Not following. There a possibility of a loop that doesn't involve time travel? Example please.
You're then referencing the 'first ever' go-around for a loop that cannot have such a thing. So that's what you mean by 'initial travel event'. There is no such thing for a loop, so I must withdrawm my 'is OK' assessment of it.
I was talking about the time before the first time travel event; before you've ever time travelled. You're talking about what happens if (or after) you time travel, so you're not talking about the time before you've ever time travelled.
Quoting noAxioms
Why can there be no odometer on the time machine counting jumps?
Quoting noAxioms
What's the contradiction?
Quoting noAxioms
Sorry to be unclear again. What I meant was: how could I be in the past as a time traveller prior to the first use of the time machine.
Quoting noAxioms
What are these different causal rules? There are still causes and effects, it seems. The older self can teach the younger self about time travel technology and the younger self can then use that knowledge in order to time travel from the future to the past. Or, the younger self can steal a time machine from the museum and then later use that time machine in order to donate the time machine back to the museum. The only different causal rule appears to be that there can be no first time travel event or that we are not allowed to talk about the first time travel event, for some unspecified reason.
So some causal rules are okay, but not others? We may never ask/explain how a time machine came into existence in the universe, but it's okay to ask/explain how a time machine came into existence in a museum?
Quoting noAxioms
It's logically self-consistent as long as we never consider a loop as having a first time travel event or what preceded it, it seems. But how is it logically self-consistent that there was never a first time travel event? Does time or causality work differently in these scenarios such that it would be impossible to trace back to the first time travel event? If so, then how do time or causality work differently? Why is it impossible to trace back to the first time travel event? Or, why can't there be a first time travel event?
Quoting noAxioms
How is it "not true"? It doesn't seem to me that it's not true; it seems that you just want me to ignore it.
Quoting noAxioms
We're dispensing with evolution, too? I'm unfamiliar with those movies/scenarios.
The scenarios in the SEP article and those I've been considering all involve human time travel with a time machine. I suppose I could alter P2 to say that time machines involved in human time travel need to be created at some point. Or, better still, P2 could say that there must be a first human time travel event associated with the human use of a time machine or time travel device/technology (assuming that any such events occur).
Quoting noAxioms
You are effectively telling me to ignore how the time machine came into existence originally. That doesn't "falsify" P2.
Quoting noAxioms
There is no problem in saying that time machines or waffle irons have always existed in a causal loop, which is what you suggest when you say they are uncaused. This wording need not imply that these things exist at all times. My point, however, was that time machines, like waffle irons, are man-made for a particular purpose, and so it seems unlikely that they would naturally exist without any human (or other sentient beings') intervention. Also, I note that we were talking about human time travel using time machines until recently, but now you're invoking fanciful beings that can time travel without any time machines and other magical shenanigans in order to try and save the "self-consistent" logic of causal loops.
Quoting noAxioms
Am I supposed to be the guy in the box/time machine, because this doesn't sound like a causal loop; it's just a guy using a time machine to go back in time every 8 seconds to do the same thing repeatedly. It's unlike the other causal loop scenarios because it's not clear that I ever become the guy in the box/time machine. Or was that part left unsaid?
Anyhow, I thought by "un-created" you meant that the time machine was not created or did not exist. Did you mean "uncaused"?
Quoting noAxioms
Right, that's why I've been arguing that time travel only makes sense on multiple timelines, and why I've been arguing that a causal loop (or that time travel on a single timeline) does contradict its existence. I don't see why I should ignore there being a first time travel event just for the sake of maintaining the consistency of a causal loop. I'm arguing that they do contradict their existence.
Quoting noAxioms
No, I was just trying to restrict it only to causal loops that do involve time travel, in case you were about to bring up any causal loops that don't.
OK, Bob makes the machine and uses it to go from 2024 to a new timeline starting at 1990. Any point on the original timeline before Bob vanishes from it is the time before the first travel event. There is no time on the new timeline before the first travel since it starts there, kind of per last-Tuesdayism.
I lost track of the question about this 'time before'. Are we talking about say 2023 on the original timeline or am I still getting it wrong?
There can't be one on the machine that jumps in the loop. Bob's machine can have an odometer, no problem.
The contradiction: Suppose, just before the jump, the odometer reads x. It arrives at its destination (8 seconds in the past in my popper example) and immediately increments the thing to x+1. This contradicts it leaving 8 seconds later with a reading of x.
Just repeating the same question doesn't make it clear. Are we talking about Bob and the copy-timeline scenario? If so, you need to specify which timeline you're referencing when talking about one thing being prior to another.
In general, if one considers that Bob builds the machine and first uses it in 2024 and uses it to go to 'the past' (no timeline specified), then since 'the past' is typically considered to be prior to 'the present', Bob is in the past as a time traveler (in 1990 or whatever) prior to 2024 since 1990 is often considered to be prior to 2024. So that's how he's in the past prior to first using the thing. It's the whole point of the machine to be able to do this.
That's what you are apparently trying to figure out. I don't know either, so I'm also exploring. What I don't do is presume the usual rules, such as that a place that almost looks like the state of things in 1990 is prior to the state of things in 2024. I also don't presume that the cause of a thing is necessarily prior to the thing. That's a pretty obvious one to throw out.
Agree. We're trying to keep that. The loop is causally closed, so I don't see it as a contradiction. The cause of the 8-second guy is his own travel event 8 seconds later.
There is no first time for the loop, or if there is, it's the only time. There is after all but the one jump, per the external timeline, presuming its a simple loop. Only the machine's timeline has multiple jumps, plus its contents if those contents go from arrival all the way back into the machine at departure.
The ones not OK lead to contradictions. The looping machine having its own 'first time' leads to a contradiction. It would effectively be an odometer going from 0 to 1, and we showed how that is a contradiction.
It came into existence by traveling from 'the future'. You can ask and that's the answer. That universe allows that sort of causality.
By being donated of course.
I think the rule you find hard to discard is that all seemingly artificial things must somehow be invented and assembled at some point, and the examples we show are consistent without all those steps. Sure, the machine is built in the teaching loop, but the technology knowledge (the inventing) is the loop, information that is never gleaned, but is merely passed on.
You're trying to find a logical inconsistency, and I don't see one. Before the loop, the machine simply doesn't exist, nor does it after. The 8-second machine exists but for 8 seconds. Not time to study and figure out how its done, something the museum guys might decide to attempt.
The same way that the lack of the most eastern point isn't a logical inconsistency? It's only inconsistent if you presume there must be a first time (on the machine's timeline), so that's apparently a wrong thing to presume. There's a first time on the world's timeline. Isn't that enough? This presumes that the external world is itself not a loop. There are hypotheses that suggest otherwise, a sort of cyclic model of the universe.
The infinite-age universe hypothesis similarly suggests the impossibility of tracing back to a first event. A loop without a beginning is not in contradiction with anything.
It's true in our universe because I cannot think of a scenario where at some earlier time there is not a mug, and at a later time there is a mug, and that there it a beginning to the mug's timeline. The timeline of the mug and that of the rest of the universe is completely parallel, so there must be a 'first moment' for it. In this alternate universe, the mug timeline might not be parallel. It still has a first (and only) time in the universe timeline, but not on its own timeline, which isn't parallel to the one 'outside'.
If a machine that loops and is never created can exist in some consistent way, then so can a creature than has no evolutionary ancestory. It just appears from some retrocausal event, and its existence somehow eventually plays a role in that eventual retrocausal event.
So it's like humans have no evolutionary ancestors (despite the biology folks suggesting otherwise). But some time far in the future, when humanity is near its end but they develop time travel, the put a couple back to year -4000 and name them Adam & Eve.
Geez, the religious folks would jump on this if it wasn't supposed to be blamed on God instead of retrocausality.
OK. The 8 second machine is created in front of me at some point, and un-created 8 seconds later when it vanishes. Works for me.
Dangerous to use the word 'first' when the temporal ordering of things is not objective. I think that's where a lot of the trouble comes from.
Nope. It came into existence when it first appears, not 'uncaused'. It doesn't exist at any time before that, so that is it coming into existence. It gets donated to the museum some time later and yet later is stolen and vanishes from existence forever after as it causes the earlier event.
I just made them up as another example which isn't directly self contradictory.
I should probably withdraw my language that these things are not created. They are, but the causes of their creation are events that are future events as measured by the world-outside timeline, a timeline which we are presuming to be reasonably linear and therefore orderable.
No, you are the spectator who has somebody use your popper and then take it from you. The person in the box is, well ... something else. It is along those lines that you should tear this apart. A human makes a great odometer, and you can't have an odometer, so the guy is perhaps not human?
Yes to the first. No, it's never you. You're left behind being befuddled, remember? You never see him again. It very much is a loop, and a very tight one.
Un-create means to cease existing. From the perspective of the linear timeline, Any traveler uncreates his machine and himself. It's just gone leaving not even disassembled parts. Of course on the machine's timeline, it just has an external environment change and isn't an act of creation or uncreation at all.
Somebody could catch a video of uncreation on their phone. You're were taking a video of a train crossing because you heard a train in the distance. The video records a blue car suddenly appearing (an act of spontaneous creation) at the crossing which then crosses and continues on. The lights go on and the gates come down, just as an identical blue car pulls up and vanishes (uncreates) at the exact spot where the prior car appeared. You have a video of time travel in action, and it even worked in the universe of Bob where a new timeline is created each time. The video is subsequently sold to the time machine sales people who use it to pitch their product.
For the most part I agree. But single-timeline travel isn't necessarily contradictory so long as one does not make choices known to be different than those made before. It does require a sort of lack of free will as it is often defined.
Any loop in time is contrary to the sort of linear ordering of all events that we find intuitive. No, it doesn't have to be labeled 'time travel'. A cyclic universe is a nice loop that isn't considered time travel because there is no linear timeline laid alongside the loop.
Hypothetically yes.
Theoretically? That's the question.
Realistically? Let's gain the ability to travel 99,9% of the light speed first...
Yes, we are talking about the original timeline. As I said earlier:
Quoting Luke
I think you've acknowledged this is not possible. It is why I was arguing that more than one timeline is required.
Quoting noAxioms
Sorry, but I don't see the contradiction. The time machine starts with an odometer reading of x (representing the number of time travel "trips" made by the time machine), then it makes a (another) time travel "trip" and records a reading of x+1. Why does it need to revert to a reading of x again 8 seconds later? Isn't it correct that the number of "trips" made by the time machine has increased from x to x+1?
Quoting noAxioms
On reflection, I want to reject my suggestion that there is more than one timeline. You've helped me to see that this is not really what I had in mind. What I have in mind is that there is only a single timeline but that the effects of the first time travel event overwrite the past of the original timeline (starting from the destination time of the time travel event, e.g. 1990). This might create a causal loop or it might not. However, the main idea I've been trying to convey all along is that there must be an original version of "the past" prior to the first ever time travel event, which gets overwritten and is necessarily different to the version of "the past" that exists post-time travel. This helps to retain "normal" causality, thus removing the need for the magical appearance of time machines or technology "out of nowhere", existing uncaused (as in a causal loop) and thus removes the impossibility of killing one's own grandfather (as in the grandfather paradox). It also removes the unpopular idea that time travel creates a "copy" of the original timeline. And it retains free will.
In fact, causal loops can be avoided in the examples we've discussed because the time traveller can just do something differently at any time after any of their time travel events. For example, there is nothing forcing the 8-second guy to time travel again after 8 seconds.
Quoting noAxioms
Perhaps they're logically consistent, but I find the magical, uncaused existence of the causal loop universes (and their contents) to be too far-fetched and unsatisfactory. Someone who gets their time travel technology knowledge from their older time travelling self does not explain how the older time travelling self got this knowledge in the first place, before they first time travelled. And I find the idea that there is no first time travel event unrealistic.
Quoting noAxioms
That doesn't explain how the time machine was created for the time traveller.
Quoting noAxioms
I'm not using 'first' as an objective ordering of things but as a human ordering of things. I don't assume the determination of a 'first' event is independent of some group of language users (particularly, English speakers).
Quoting noAxioms
It has a first appearance?
Quoting noAxioms
But is single-timeline travel necessarily contradictory, even if one does make different choices post-time travel?
Given physics where there is a timeline that is the original one, that line cannot have a time traveler in it at all. All the copy lines have but the traveler(s) that created that line (assuming the machine had one or more passengers). So in those lines, any traveler was already there at its start.
Given the physics of a single timeline, various machines might travel here and there, but there would be presumably some earliest one (to see dinosaurs say). In such a situation, there is no traveler before that earliest Cretaceous period. I don't think you're asking that, but who knows...
There are valid scenarios with such a single timeline, but the traveler (if it is human) is part of 'the past' then and lacks the free will to do otherwise. I agree this runs into serious problems if he knows what he does (say a minute ago) and goes back explicitly to do a different thing. No amount of determinism is going to prevent that. Determinism is not a thing with a will different than yours. Nobody seems to realize that.
Because it reads x when it appears 8 seconds before that. You know that. It's on the outside and you read it. You can't read it being x, x+1, and all the other numbers. The number has to match at both ends, or it didn't come from that 8-seconds hence jump. It wouldn't be a loop, just a stopover, and a different party popper than the one he took from you.
OK. That's not something we discussed yet. How does it empirically differ from the branch thing? The old 'history' goes away, so there's nobody to witness the population of the world going down. There are a whole mess of uncaused events going on, but besides the classical impossibility of that, no other contradictions. You have people who don't have valid identification. Maybe no other people at all. So the empirical experience of those you don't take with you is irrelevant, and the empirical experience of the traveler is identical to the experience of the guy in the branching model. So this sounds like a different interpretation of the exact same experience.
Those are just my thoughts before going on to read what you said about it:
OK, back before the earliest time, before the destination of any retro-time traveler.
Or do you mean 'first' on the timeline of some traveler instead of on the one world timeline? You don't ever specify. I think you mean the latter, in which case, what do you mean by 'must be'? How can something 'be' if it doesn't exist at any time? What definition of 'be' are you using?
Suppose I travel to 1990. How is what you call the original line (the one I remember with cellphones and all) is 'the past'? It's not before 1990, and for that matter, it's not after either. It just isn't at all.
It all sounds like a re-growing-block model, except that disallows forward time travel since the destination specifed doesn't yet exist. I set sights for the year 3000 (like in Futurama), but while my machine is waiting for Y3000 to come around, somebody else uses a time machine to go back to 1985, thus obliterating me and the destination I targeted. same fate awaiting all those people paying for cryonic preservation. It requires a stability that just isn't there.
But all your scenarios describe exactly that, including pretty much every fictional story that I can think of. Time travel, as envisioned, necessitates technology or at least some object/person appearing uncaused from nothing, or worse, replacing what was otherwise at that spot. Remember terminator? This sphere of space replaces what was there with some air and a naked person. Nobody says what happens to the stuff that unfortunately happened to be where that ball appears, which by chance might possibly be half of another naked person.
Well, the paradoxes are gone at least. Nobody can demonstrate the typical definition of free will.
They'd not be loops at all then. The 8-second guy would simply die in moments the same way the half-of-naked person did. It's a hazard of living in such a world is that your life expectancy outside the machine is moments at a time, and no better inside the machine since no time passes in there (unless you assert otherwise I guess).
It's not created for the time traveler any more than the time traveler is created or has an age.
8 second guy has a first and only appearance, yes. From his looping timeline, there is no first anything. It's a circular timeline.
What you describe above is a single preferred timeline scenario, with all the non-preferred timelines being nonexistent. I am not sure if there are 'different choices' involved since there is but the one timeline, and thus one choice being made at any point in time. Sure, you remember making different choices, but those are memories of nonexistent times.
It looks like we're saying the same thing.
However, this does not explain how a time traveller can have travelled to the past before their first ever time travel event. Bob will one day grow up to build a time machine, but before he has ever grown up or built his time machine, his older self appears from the future in a time machine. If this is a causal loop, then where are the causes or the determinism that brought the time machine into existence? There must have been an original version of the past before Bob ever created his time machine in which he was not visited by his older self.
Quoting noAxioms
In the case of this dinosaur visitor, surely this person had to have been born before they could ever travel to the past? Therefore, there must have been an original version of the past that existed before the dinosaur visitor ever visited. How could the time traveller be in that past time before they had ever time travelled or before they were born in the first place? Surely, their birth must precede all the other events of their life, including their time travel event. If their birth must precede all the events of their life (given determinism and causality), then there must be a (different) version of history without a dinosaur visitor which exists until this person was born and subsequently time travelled to visit the dinosaurs. This original version of history without a time traveller gets overwritten following the time travel event, but must have existed.
Quoting noAxioms
If you consider history from the end of time, at the end of history, then obviously nobody has the free will to change any of that. Nothing more can be done.
Quoting noAxioms
If it's a causal loop, then it will repeat the same time travel event over and over again. However, the odometer reading of "x" (jumps) is after the time travel event. Therefore, if the odometer actually works, then its reading before the time travel event must have been "x-1" (jumps). This may not be part of the causal loop, but it logically (and causally) must be the case.
Quoting noAxioms
Sure, but I'm considering the possibility of time travel, not trying to save lives or the stability of the timeline.
Quoting noAxioms
I am referring to pre-time travel; before the time travel event has ever occurred. Before anyone has ever time travelled, history will be a particular way, and this particular way (or version of history) will be altered by the time travel event to create a different version of history.
We might say or believe that up until now there have been no time travel events. If I were to time travel tomorrow, back to 1985, then I would be altering history as we now know it. After that, history will contain my time travel event, but it must also contain the "unaltered" history that preceded my time travel event (the history as we presently know it, before any time travel events). My time travel event causes the alteration of the original history, so this is consistent with causality and determinism.
Quoting noAxioms
Not sure that I understand what you mean here, but in order to make sense of your "travel to" 1990, you cannot already have arrived at 1990 (as a time traveller) before you have time travelled to 1990.
Quoting noAxioms
To simplify matters, we might only consider one time travel event rather than several. Also, in this discussion I'm interested in the possibiilty and consequences of time travel, not in preserving the stability of the population or the timeline.
Quoting noAxioms
Obviously, a time machine will appear in the past to come "out of nowhere" following the time travel event. That is not what I am talking about. I am talking about the history of a time machine's construction being erased in a causal loop, such as in the museum donation scenario. This is the sort of appearance from "out of nowhere" that I am referring to; that a time machine or its technology comes to exist without any causal history. The same applies to the dinosaur visitor who can exist in the past (which is necessarily post-time travel) prior to ever having been born (which is necessarily pre-time travel).
Quoting noAxioms
Can somebody demonstrate the typical definition of determinism?
Quoting noAxioms
Ain't that the truth.
Quoting noAxioms
I imagine the time travel duration to be instantaneous, but I don't think it's important.
Quoting noAxioms
But we can imagine how a causal loop can come to exist. For example, I spend my life working out time travel technology and build a working time machine. I then time travel back to 1990 and teach my younger self how to time travel. My younger self grows up, uses the knowledge to time travel back to 1990, and teaches my/their younger self how to time travel. A causal loop follows the initial time travel event, but it has a different history prior to the first time travel event (an original history in which I figured out time travel without having been taught it by my time travelling self).
Quoting noAxioms
Is that a "yes" or a "no" on the first?
Quoting noAxioms
But logically (and causally), those non-existent times did exist, prior to the time travel event.
And as I said, the empirical experience of everybody is the same between the copy/paste interpretation and the 'alter the original' interpretation. Either way results in a general de-population of Earth from the travelers PoV, or if the use of the machines becomes commonplace for everybody.
That's interpretation dependent. Empirically, the guy will remember being born, sure. Given the copy/past interpretation, yes, he was actually born in some timeline somewhere, one of many, but not this one. In the alter-history interpretation, no he was never born. That state doesn't exist in the one timeline. No earlier time had his birth in it, and only an earlier time qualifies for that verb tense.
You are using past-tense in a mixed way. Be specific. In the linear timeline, there are dinosaurs and a time machine that has appeared uncaused, all in the present. There are no other people on that timeline unless the guy brings a breeding population with him. Nobody was born. There is no 'must have been' about it since earlier times do not contain his birth.
On the traveler's timeline, there is a memory of a birth, a memory of a time that doesn't exist. Memories are thought of as 'past; things, so one could meaningfully said that he must have been born, but it's more like Adam and Eve and insisting that they must have been born which reportedly they actually had not. One wonders what their very first memories were. Did they have to learn to eat and not poop in your bed and had invent language? Our time traveler seems to have all that experience already, so he's better off.
Again, on which timeline are you measuring this? Given a time machine, this would obviously not be true or a calendar timeline. Marty is in 1955, well before say 1968 when he is born, contradicting your statement.
On Marty's timeline, he is in what appears to be 1955, and has 17 years of memories, which include stories of his birth. If the memories were perfect, yea, he'd remember that birth. Whether that birth event actually exists is a matter of interpretation, just as is my birth event. Per last-Tuesdayism, there is no way I can prove that I was ever born. We all just assume it by convention.
Only from the PoV of the machine and its contents. Per the outside observer, there is but the one jump. Yet again, you need to specify which timeline is being referenced when making statements like that.
Contradicting the fact that you just said it reads x+1, a number to which it was set 7 seconds ago and not altered since. That would be a contradiction, and thus cannot be the case.
Concerning the 'rewrite the one timeline' interpretation:
OK, on hte Earth timeline, we're talking about dinosaurs then, just before the machine appears somewhere uncaused with an odometer reading 207. Before that Cretaceous time, no time travel event has ever occurred. History is a particular way then, but the Cretaceous is the present, so it goes only that far, and the rest is yet to be written.
The time travel event (the appearance of the box) only has a causal effect on subsequent events, not on the prior ones that are the 'history'. The machine doesn't alter history, but it truncates it to a point and starts a new rewrite.
None before the Cretaceous, no. We don't know that, but we have strong reasons to believe it. Any prior time travel event would arguably have to have been made by something not human or human-created, and probably wouldn't be on Earth.
That, btw, is another problem rarely addressed: How does the machine know where to go in space? Almost all the stories have them setting only 1 coordinate, not 4. Earth is moving. If I just back a week, what reason do I have that it will also transport me sideways to where Earth was (the surface of it no less) a week ago?
The word 'now' in that sentence is ambiguous. Presumably you are still planning to go back to 1985, and thus it is still 'now' 2024, and there is still a 'we' to know such things.
If the action has just been done, then 'now' is 1985, there is no we, and there is no history to be known, although you do know of it as a sort of fiction.
You mean 1984? Yes, it contains that. If you mean 2023, then now, since it is now 1985 and 2023 has yet to be, and least per this 'rewrite' interpretation.
You seem to be trying to refer to what was the original timeline in the branching interpretation. If you've switched back to that, you need to indicate so, but I think not since you're explicitly referencing the alteration (truncation) of the original line.
It is now presently 1985 and there is no 'we' there, so no, that statement makes no sense.
Traveling to 1990 and arriving there is the same thing. That arrival event IS the time travel event. Are you talking about a different jump? Before that is 1989. 1991 is after that. The traveler has a memory of a nonexistent 1991, it being nonexistent because it's a future time, yet to actually be.
If you're interested in consequences, you need to address the case of multiple machines crossing each other. I thought we were deliberately ignoring the lack of possibility. If you're actually interested in it, then exploring consequences is moot until you find a way that it's actually viable. SEP seems to suggest that pacing counts, but that's hardly something with interesting consequences.
Again, it doesn't follow a time travel event, it is the event. If you're talking about the departure event, the appearance of the machine in 1990 does not follow that event. 1990 is before 2024.
The loop does not erase its construction. It isn't something that is constructed at all. It's a solid example that 'things' in that universe don't necessarily need a construction phase.
It has a causal history. It's just a retro-causal history is all. As I said, you're going about finding the inconsistency all wrong. Stop trying to find the end of a loop that doesn't have one. That's not where the inconsistency is.
He was necessarily born pre-Cretaceous? That makes no sense to me. It can make sense in the branching case, depending on how one chooses to order events that are not on the same timeline.
That is QM (or time) interpretation dependent, and no,. there is no way to falsify the interpretations that are not deterministic in one way or another.
Why? He's already got the first 'you' teaching him. How many of you does it take? You're not making a loop by doing this. You're making a crowd control situation.
Well, you just had two different people (both you) time travel to the same spot. What if the coordinates are exact and second one obliterates whatever was at the spot at which it appear? I mean, you've never really specified what happens when the machine pops into existence somewhere. What happens to the bugs and other contents of that location? If there's a person there, or half of one, or the middle of a jet engine in flight? What if you manifest a mile underground? Never mind you being somewhat stuck, but what happens to the rock that was there a moment ago?
From the world timeline, it's a yes: first and only. I said that. From the circular timeline, there is no first.
I don't see how they can both be nonexistent and also 'did exist' when the time of their existence hasn't yet happened. Nothing at those times exists yet. That's the nature of 'the future'. It's what makes using the same machine to travel to future times somewhat contradictory. It would have to just go into a stasis state (Per Larry Niven's universe), wait for the prescribed time, or in the case of Niven, waiting for conditions outside to be non-fatal. The thing is, where is the machine while it's doing this? Can others see the box waiting there, or does it vanish into another realm while it waits for its destination to come into being? And of course, what happens if the departure in history suddenly ceases to be a part of history?
I thought your post was too large, but mine is even larger.
The word "timeline" is, of course, vital in the study of history. Over an era there is a timeline of wars, a timeline of governance, illnesses, etc. But the word used in this thread is a many-worlds fabrication. Its twin brother is "alternate history".
Is there any evidence of the existence of timelines in the physical world beyond time dilation?
I'm not sure what you mean by "spawn new timeline scenario". Two posts ago, I rejected the view that there is more than one timeline. However, I retain the idea that there must have been one version of history before any time travel events and a different version of history after the first time travel event (a history which henceforth includes a time traveller), at least different starting from the destination time of the time travel.
Quoting noAxioms
In this context, the present is simply the departure time of the time travel event. The time traveller departs from the present and arrives in the past.
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The time traveller does not depart from the present of the spawned timeline, but from the present of the original timeline. They travel to the past. Assuming this is the first time they have ever used the time machine, then they were never in the past (as a time traveller) prior to this departure.
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He did travel to the past from a time which is in the relative future of that past time. He did not travel to the past from a different timeline; his time travel will change the history of the same timeline. The changes will begin from the time traveller's date of arrival, starting with the addition of the time traveller in that time.
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Right, nobody has yet time travelled (that we know of). If they were to time travel (at some time after this present time), then they would alter the past and present as we know it.
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If I were to make the first-ever time travel journey tomorrow to arrive at the destination time of 1985, why would the population suddenly decrease from my POV as a result of the time travel? I don't believe you think it's only because Earth's population was smaller then.
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There's only one timeline.
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Why was he never born?
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Why not? Aren't we considered to be on one timeline? Are we never born?
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Okay, in the linear time there are dinosaurs, and a time traveller and their time machine have appeared uncaused. Nobody was born, yet the time traveller exists. How is this consistent with causality and determinism?
The only logical sequence of events is that the time traveller is first born and then time travels to visit the dinosaurs. This implies that there must exist a linear time without any time traveller up until the time traveller's birth and subsequent time travel. THEN, when the time traveller visits the dinosaurs, they change the history of the timeline from what it was, without a time traveller, to what it is, with a time traveller.
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I don't know why you keep bringing it up, but your religious references are wasted on me.
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In this context, I'm measuring it on the traveller's timeline; on the linear sequence of events of a person's life. Marty must first be born in order for him to time travel. This is true given a time machine. He cannot travel back to 1955 until after he is born.
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Being alive is pretty good evidence of having been born.
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I didn't say that it reads x+1. I asked you to clarify the contradiction of it reading x+1. I acknowledge that it would always read x in the causal loop, but logically, since you say that the guy in the box has time travelled, then it must have previously read x-1 prior to its time travel (assuming the odometer works).
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The time machine's appearance in the Cretaceous period is not uncaused. It's appearance is caused by the functioning of the time machine, which enables it to transport a traveller from some future time to the Cretaceous time.
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I agree that the past is only altered from the time travel destination time onwards (or from the earliest destination time onwards if we are considering more than one time travel event). I thought I had said this previously.
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The time travel "action" hasn't "just been done". As I said, the time travel "action" will happen tomorrow. Now is 2024.
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No, I mean the 1985 without any time travellers that currently exists prior to any time travel event. Since I'm time travelling tomorrow, no time travel has yet occurred, which means there are/were no time travellers in 1985 according to history as it currently stands. Tomorrow's time travel event will change all of that history, because there will henceforth be a time traveller in 1985.
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No, I'm not talking about a different jump. This is no different to saying that you cannot have arrived in Paris (as a space traveller) before you have travelled to Paris. Likewise, you cannot have arrived in 1990 (as a time traveller) before you have time travelled to 1990.
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I am talking about before the time travel event, not before the destination time of 1990. As I said, you cannot have arrived in 1990 (as a time traveller) before you have time travelled.
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It seems like it's confusing enough to discuss one time travel event. Why compound the confusion by discussing more than one? Let's agree to the consequences of one time travel event before we discuss more than one.
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The time travel event is both the departure of the time machine from 2024 and its arrival in 1990. I can refer to it as a time travel "journey" or "trip" or "jump" instead of an "event" if you'd prefer. It is a bit of a quibble to say that the arrival of the time machine is no different to the appearance of the time machine such that I cannot refer to the appearance of the time machine as being an effect of the time travel event.
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The arrival of the time machine in 1990 does not follow its departure from 2024? But isn't that exactly what a time machine does?
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If you can suspend disbelief, I suppose.
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Okay, then where is the inconsistency?
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He was necessarily born before he time travelled to the Cretaceous period. Again, by "before", I'm talking about what happens before the time travel event; or better still, before the time machine departs. What I'm saying is that the time traveller must be born before the time machine departs (with the time traveller); I'm not saying that the time traveller was born before the Cretaceous period in linear time.
Quoting noAxioms
The first "me" was not taught how to time travel by my older, time-travelling self (pre-time travel). It is only the young "me" in the causal loop who learned how to time travel by being taught by my older, time-travelling self (post-time travel).
Quoting noAxioms
Let's just assume that it works flawlessly and does no serious damage or harm. It's time travel technology and it works.
Although we would never know it.
True, but this doesn't make time travel any less possible. Also, if we were on a timeline which had had time travellers in its past then we can imagine that there might be reports or records of it.
The "If" part needs backing proofs with evidence before the whole sentence could be accepted as a meaningful statement.
So he's in 1990 despite it presently being 2024? What's it like to be in a place that isn't the present? I think the Steven King book/movie Langoliers had a plot like that.
You said you were rejecting the 'spawned timeline' idea that occupied so many of our posts.
Keep in mind that I'm not a presentist, and am sort of having fun seeing how a presentist can phrase time travel coherently.
This is the truncation I mentioned, the overwrite scenario instead of spawn new line scenario. The inconsistency is calling 1990 'the past'. If the universe is currently being rewriten from there, then 1990 is the present, and there is no original history of making the machine. Those dates have yet to be written since they are in 'the future'. So now you have a machine sitting there un-built, but not un-caused. It was caused by a nonexistent retro-causal occurrence.
The people there now have access to time machine technology, so that timeline is likely to be overwritten at any point. Eventually somebody will erase all of human existence and that will be that. It takes just one traveler going back a million years or so.
Point is, every use of the machine(s) in the backwards direction truncates history a little further. The population would empirically slowly dwindle in the branch timelines, but here you have no branches, only the original, and in that line, the present keeps moving backwards at frequent intervals.
This isn't hard. His birth event doesn't exist (assuming he/somebody/something truncates the present to a date prior to the birth date. If he isn't the guy in the machine, then he doesn't exist either (at all). So not even a memory of being born.
We're in a universe with retro-causality here, one that a cause obliterates its own existence from the one history.
That is not a logical sequence on the linear timeline. First he appears with the dinos. Then, much later, the time eventually comes that matches the year he remembers being born. There is no birth event of Bob at that time. The memory was false.
Two kinds of time mixed there, unless the history line is never truncated, and the machine simply writes the current universe a new way without traveling at all. That model (I'll call it the stacking model) doesn't easily support forward time travel, but not sure if any of them do. You ought to think about how forward works. Funny, but the stacking model does allow one to witness one's own birth. Not the actual one since it doesn't involve actual travel to the past, but a copy of it. One can restore all the people eliminated by the dinosaur stint. There are no loops in the stacking model.
So 2024 precedes year -100,000,000, a funny interpretation of the word 'precedes'.
Ah, you actually identify a line. Sure, on that line, 2024 precedes -100M. But it's just a memory. His birth event (say in 1975) is nonexistent. He can't for instance take the machine back to it and witness it.
Not if your earliest appearance was from a time machine. You keep thinking the rules of this universe apply to this retro-causal one.
From the PoV of the machine, sure, That's the same as memory. 2024 feels like 'the recent past' to the machine and its contents. If we're talking about the stacking model, it actually still is the past, and sure, the machine was in fact built at some point. That model is empirically different than the other ones we've been discussing.
Take 8 second-man, but make it 50 years. A young guy steps out the machine, and the same guy 50 years older travels back to the arrival event, and not looking like some old guy. That's an odometer, and I cannot explain it better when you seem incapable of understanding why the jump counter in a loop would be a contradiction.
Hence me saying that 8-second guy can't be human. A human ages. He can't.
Quoting Corvus
We were deliberately ignoring all that, since the possibility of this as described isn't there at all.
Quoting jgillHere you seem to be using the word 'timeline' to mean something like 'period of time'. That's not how it is being used in our posts. One timeline with Hitler losing WWII. One with him winning. Others with no Hitler. Other timelines with no humans at all, ever.
Here I think perhaps you're confusing the word with 'worldline', a term for a physical path of an object through spacetime, that sometimes comes up in discussion of relativity and block universes, although the term is not directly related to time dilation, which is just an abstract coordinate effect.
The timeline we speak of here is a specific history of everything, not just the path traced through spacetime of a single object.
Sure. The point is not a criticism or condemnation by any means. It is just to clarify the statement is unsupported in any meaningful manner without proofs and evidences, hence all the following arguments would be just speculative conjectures.
Because of the fact the premise "IF" describes the possible physical and empirical events, and also the conclusion part is soley dependent on the premise, it should have given even brief explanations how the IF part could be possible, for it to be accepted as a valid assumption for the further arguments.
Come to think of it, what prevents you from trying to prove the assumption? Wouldn't it be actually an interesting attempt, and all the emanating arguments from the proofs (if it were possible to come to some sort of proofs with evidences) would be more exciting? :D
I admit, I am stretching a point. I'm looking for any sort of evidence of change of movement through time. And time dilation shows one individual moving at a different rate, but through the same "timeline". Actually, I think of each instant as triggering an infinity of timelines, an unimaginable bifurcation that we wander through without second thought. As I punch this key I choose or create a timeline. A study of the structure of this web of timelines would seem appropriate as a prelude to this thread.
As I explained in my previous post, my use of "before" is in relation to (before and after) the time travel event, not in relation to the linear order of the timeline. But it seems this has made things unclear. Instead of having referred to timelines before and after a time travel event, perhaps I should have referred to timelines that are with and without a time travel event. It is the comparison between timelines with and without a time travel event that I wish to make. The first and most obvious difference is that a timeline with a time travel event contains a time traveller, whereas a timeline without a time travel event does not contain a time traveller.
However, the existence of the timeline without time travel must precede the existence of the timeline with time travel. The time traveller departs from the timeline without time travel and creates a timeline with time travel by doing so. The time traveller's destination is on the timeline without time travel, so the time travel event alters the timeline without time travel to become a new timeline (with time travel) from that point on, after the time traveller inserts himself into it. We can then consider the effects of the time travel event by comparing the timelines with and without time travel (from the destination time onwards).
Quoting noAxioms
If it will help make things clearer, I can try to dispense with (McTaggart's) A-series terms. The time traveller departs from the year 2024 and arrives in the year 1990.
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Yes, however, I also said:
Quoting Luke
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Keep in mind that I'm not a presentist, either. As I said earlier in the discussion and as I have explained previously on these forums, I believe that a combination of both views of presentism and eternalism are required to coherently account for time.
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The timeline is not "currently being rewritten from there" (i.e. from 1990), because I have been referring to a time travel event which has not yet occurred in 2024, but that will occur tomorrow (or at some future time relative to your reading this post in 2024). Since 1990 is in the past of (or earlier than) the present time of 2024, there is no inconsistency in my referring to 1990 as "the past".
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Why would the time machine be un-built in 1990? Did the time traveller dismantle it after he arrived?
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I still don't understand why the population must be dwindling. It's one timeline. The only way the population could be dwindling as an effect of the time travel is if the time traveller's actions somehow prevent people in the future from being born. That is not obviously the case. The time traveller could visit the dinosaurs and then be killed 5 seconds later, having been crushed by a dinosaur. I can imagine scenarios in which the time traveller somehow prevented the evolution of humanity, but it's not necessarily so.
Quoting noAxioms
His birth event does exist. That's my point: that the original timeline must still exist (in some sense) because it contains the causal history of the time travel event and the new timeline. You could think of it as eternalism for the time traveller's timeline.
Quoting noAxioms
Although the time traveller can obliterate their birth event from the original timeline, this isn't necessarily the case. But I'm not entirely sure what you mean by "a cause obliterates its own existence from the one history".
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What makes this a logical sequence on the linear timeline? How is it logical that Bob was never born and that he first appears with the dinos?
Also, an explanation is required for why Bob's birth event did not occur. His actions may have removed the possibility of his own birth, but I don't see why it's a given.
Quoting noAxioms
How is this necessarily what I'm describing? You may find it perfectly logical for a person to exist before they are born, but I do not. At least, not on the time traveller's timeline.
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I was referring to the sequence of events of a person's life. On the the time traveller's timeline, their birth precedes all the other events of their life.
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Yes, and earlier I actually mentioned another line, the linear timeline.
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Why not? Did he somehow prevent it from happening?
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Yes, I still maintain the strange rules that one must be born before they can travel to an earlier time, and that people cannot exist as adults at a time before their birth event without having first been born and then having time travelled. Why should those rules not apply?
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Then you acknowledge that the appearance of the time machine in 1990 does follow its departure event in 2024?
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I do understand why it would be a contradiction. As I said, I acknowledge that it must read 'x' jumps in the causal loop. I'm just saying that it must have read 'x-1' jumps prior to the time travel (which happens outside the causal loop).
Physics mathematically allows for tachyons, which can 'go backwards' in time, but nobody has ever found a tachyon or other necessary exotic matter such as things with negative mass and such.
I suppose in the end it would matter how it works, before we go about presuming the properties and possible interpretations of the thing.
Quoting LukeAgain, I thought you were abandoning the interpretation with creation of timelines in favor of modifying the one and only line.
I thought of a simple killer for the modify-original timeline: The universe would end pretty much abruptly any time the machine was used to go back, but in a way that doesn't prevent the departure event.
Back to the train tracks, Alice gets there just as the gates go down, but watches a very similar car ahead of here make it across. So she hits the button and goes back 30 seconds. That destroys the 30 seconds. She ends up at the tracks, and in time to scoot across. The world ends 30 seconds later when the car behind here truncates it there. There is no future after that. The universe cannot go on.
So if that's how it works, using it is a doom to any future event unless you end up in a world where no further use of the machine will ever take place.
Maybe we should go back to the spawn-new-timeline model, which has infinite series of Alice crossing those tracks, but at least each of them gets to her appointment on time.
Seemingly an admission that time travel with presentism don't particularly mix. I mean it does. SEP discusses it, but says very much that the arrival event occurs decades before the departure event, back when the arrival event was the present, which only happens once. That model doesn't have a history between those times where time travel hasn't yet happened.
You use a lot of A-series terms, which make no sense without presentism. Yes, learn to dispense with the concept. It helps. There's no evidence for it other than intuition, a pragmatic lie that makes us fit.
The branching model works reasonably well in a block model.. There's no obvious correct way to compare moments between timelines.
Maybe. I mean, it;s not possible, so you'd probably get a hard contradiction with eternalism as well. Doing so given an impossible premise wouldn't falsify either view.
I don't mean disassembled. I mean something exists which never came into being. But this is in the truncate-model, which I'm rejecting because we could never have existed in such a universe.
I know you consider the machine to have been built, despite that process not existing, and 'was built' (a past tense reference) 30 years from now. As Dr Who said in his Xmas party: Didn't you get me this next year?
I noticed.
But that's just a memory. It is a memory of nonexistent events.
His birth event (say in 1975) is nonexistent. He can't for instance take the machine back to it and witness it.
Yes. A machine appeared in the Cretaceous and humans evolve only on the timeline without the machine.
Quoting jgill'Change of movement through time'. What an interesting way of putting it. You'd like the SEP definition of time travel then, which is whenever clocks don't agree for reasons other than a faulty clock.
Funny thing about time dilation is that there's no way to tell which individual is the one 'moving through time' at the faster or slower rate.
"Time travel" has been beaten to a pulp through pulp science fiction. I like "timelines", but only those I initiate. Time is like a murky, viscous liquid that covers your feet - the older you get the harder it is to make progress.
Yes, I have.
Quoting noAxioms
Could you explain further why the universe cannot go on? I don't follow. This is a causal loop, I take it? You said that a causal loop only appears to occur once for any outside observer. How is the rest of the universe destroyed or affected?
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No, I think most people understand that time travel involves departing from the present time to arrive at a past time without them being confused about which is the present time. I offered to speak in B-series terms because you were being difficult about it and because it makes no difference to my point.
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Does that mean we can't think about it, then? Is it impossible that there was a period of time before time travel first occurred; before there were any effects of time travel?
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Is it so difficult to distinguish a timeline which contains a time traveller from one which does not?
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The time machine has time travelled from 2024 to 1990, so why would it be un-built in 1990? It seems that you now wish to simply reject the possibility of time travel out of hand.
Also, I don't know what you mean by the "truncate model". You still have not yet fully explained how the universe truncates or ceases to exist or how the population dwindles following a time travel event.
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Well, how do you account for their adult existence at a time which is earlier than the time of their birth? Was a time travel event the cause, or was it some other cause?
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Why couldn't he use the time machine to witness his own birth?
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Are you saying that humans did only evolve on a timeline without a time machine, or that humans can only evolve on a timeline without a time machine. If the latter, then why can't humans evolve on a timeline that has a time machine in the Cretaceous period?
For a trivial implementation of the time-travel variant, say that whenever a player passes Go, he is forced to land on Go and must wait for the other players to finish the loop. After all players finish the loop, their individual wealth is reset to that of the beginning of a new game (£200?). During the next iteration of the board, the players must perform exactly the same actions as they did in the previous iteration and must re-use the dice-values they previously rolled.
Obviously that example is completely useless and boring, but it expresses the desirable property of an iteration of a Monopoly time-loop, namely that the iteration of the loop is stable, in the sense that the next iteration must proceed in exactly the same way as the last.
To put this condition more generally, a stable iteration must be a fixed-point of some functional F of the players combined observations and decisions. In the case where we always restart the players from Go and reset their wealth to the beginning of game and force them to play as they did in the last loop , then every possible iteration of the board is a fixed-point, since there is no new information leaking from one iteration to the next. This corresponds to setting the functional F to the identity functional.
So the challenge of Board-game game design here, is to design a functional F that allows partial leakage of information from one iteration to the next, such that players have freedom to make decisions that spans several iterations of the loop, albeit with that freedom decreasing from one iteration to the next as the game converges towards a fixed-point, such that the result of the game expresses time-travel, or rather a time-loop, although the iterated gameplay beforehand does not.
Tachyon is a hypothetical object which is in the domain of a fiction.
Quoting noAxioms
In Modal Logic, when you say X is possible, it implies that X was possible in real sense. For example,
X = I can order wine instead of beer.
X =I can have pizza instead of sandwich or McDonald.
X = I can read Hume instead of Kant. These are all possible options that can happen in real life. It is just a matter of one's choice, hence legitimate ground for being premises for further discussions.
But if X = I can walk on the planet Jupiter, or I can fly faster than light. then it would be rejected by most people unless there were some explanations on how that would be possible, because there is no logical ground or scientific possibilities for that statement to make sense on their own out of blue. Therefore it is not fit for being a premise for any intelligible discussions.
But the ability to merely affect, or rather to construct the past is a weaker condition that only stipulates that the past is a creation made out of available information, including information that is the consequence of players present and future actions, but it doesn't assume that the revealed information is mutable.
Of course, a mere mortal cannot know as to whether the information at his disposal "comes from the future or the past", in order to rule out the possibility of him using that information to cause causal contradictions, and this epistemic restriction isn't modeled in the suggested time-lords game I previously suggested, which grants players transcendental knowledge of the future/past distinction and merely forbids them from acting upon it.
The only means of eliminating temporal omniscience from the game, is to restrict the game to a single iteration of the board loop. But to distinguish the resulting game from a case of single-iteration classic monopoly requires a different approach to the rules and constraints. For example, by granting a random event such as "Bank error in your favor, collect £200" the capacity to impose constraints onto the future actions of the players. Say, by that event triggering the potential introduction of a "cause" card into a deck of cards that some player is guaranteed to draw in the future (but without his prior knowledge).
It is a hypothetical object in the domain of science. Can't help it if the fiction folks are the ones that latched onto it.
The particle is lumped onto various headings of 'exotic matter' (including various virtual particles), and exotic matter is seemingly a hard requirement for time travel.
Quoting Corvus
Closed time loops are valid solutions to Einstein's field equations. They would probably involve exotic matter, and would already be there, forming small close time loops. Classically (unrealistic), this is equivalent to a 'rift in space & time' (definitely a fiction term), sort of like in the Kate & Leopold movie. There's no machine, no punching in a desired destination. You just compute where and when they are and leverage them.
They have quantum teleporters, which means they actually have teleported a small object from here to there. Do that with a worm hole and you have retro-causal information transfer. If you can teleport a small thing, theoretically you can do it to a big one. Something is sent from one teleport booth to the other, so send that 'something' through the wormhole and reassemble your person, Amazon package, or whatever you're sending.
None of this rewinds reality, but actual retro-causal (or FTL) information transfer opens things up to paradoxes.
Nobody has ever detected what would be considered a wormhole. A lot of this stuff can be verified only by privileged verification, where only privileged people can possibly test certain things, and there is no way to convey the results of the test to non-privileged people. For example, I posit the existence of an afterlife. So you die, and if there's an afterlife, you know it but can't tell those still living. If there is no afterlife, you can't be in a state of knowing that.
Presentism is another example. There's a test: Jump into a large black hole. If you can be in there, presentism is falsified to you, but there is no way to inform those outside (the non-privileged folk) of this finding. If presentism is true, then like the lack of afterlife, you can't be in a state of knowing that.
Quoting LukeYour new suggestion says that the original (and only) timeline is truncated back to the destination event upon somebody time traveling backwards. If it subsequently (30 seconds later) is truncated again, by 30 seconds, then there is no way for the history of the timeline to grow beyond any backwards travel departure. The only way for it to go forward significantly is if there is never again a backwards time travel event. I don't know about forward time travel You've given seemingly no thought as to how that might work.
This is a different kind of loop since it doesn't involve the same machine traveling over and over. It only makes but the one trip. That's enough to end the universe, according to the 'rewind/truncate' thing you've been pushing lately.
I didn't say destroyed. I say it ends. Your idea posits that: If I go back to 1990, everything from there to 1990 ceases to be part of the universe. Is not the entire universe affected by this, or do we just rewind some limited region like Disneyland? So now everyone in Disney thinks it's 1990 (they're pretty good at that sort of thing), but people outside the park think it's still 2024. That's not time travel, it's just fooling the guy in the machine by putting him in a live action role playing game.
You can, but it would be really nice if the discussion was free of more contradictions than just the impossibility of time travel (besides the pacing).
There is but the one timeline, unless we're changing stories again.
It's your model, the one you are not pushing instead of the branching model. You didn't really give it a name, so I did. In it, travel to 1990 deletes 34 years of history and lets it all get rewritten again, but with a different 1990 state this go around. That 34 year scenario might well not end the universe, if the second go around can not only destroy that machine, but preventing anything anywhere (including other galaxies) from ever making one. This cannot occur in the 30-second story with the train tracks. No way to stop that one, so the universe ends there.
In the context you didn't include, it was because he travels to a time before his birth, thus altering 'history' to one in which he (or any other human for that matter) is never born.
They only evolve from a Cretaceous state that doesn't include a time machine, yes. More precisely, humans don't evolve from a Cretaceous state that is in any way different than the Cretaceous state from which we evolved. That's popularized by the term 'butterfly effect'. Chaos theory is very clear on points like this.
Quoting jgillAnd what definition are you using this time? What is this sort of timeline, and how does one go about initiating one?
I've never said that the timeline is "truncated". By "truncated", do you mean "shortened"? In what sense is the timeline shortened? What I'm suggesting is not significantly different to Marty McFly's time travel in Back to the Future. I don't see how he "truncates" the timeline after his time travel to 1985 or why the history of the timeline would be unable "to grow beyond any backwards travel departure" after one or more time travel events.
Let's say the time traveller travels from 2024 to 1985. The time travel event will change the history of the timeline from 1985 onwards, compared to the history of the timeline as it was before the time travel event took place in 2024. But I don't see why any time after 1985 should not exist, post-time travel. Unless the time traveller does something catastrophic, then I would imagine that many of the same people will be born and many of the same things will happen as they did prior to the time travel event's occurrence in 2024.
On that note, do you agree that the time travel event does not occur until 2024, given that the time traveller departs from 2024 to arrive in 1985? The time machine is not used, or perhaps even created, until 2024.
Quoting noAxioms
I haven't been "pushing" this "truncate thing"; you have. And the "rewind" thing is just time travel.
Quoting noAxioms
Where did I say that "everything from there to 1990 ceases to be part of the universe"? I've said only that the time travel event would change the history of the timeline, starting with the time traveller's insertion into the earlier time (as a time traveller).
Quoting noAxioms
There is but the one timeline, but the history of that timeline must be able to be altered by a time travel event. That is, if 2024 is the departure time and 1985 is the destination time, then there was originally a 1985 without a time traveller, until 2024 when the time traveller departed and returned to 1985. This is what time travel involves. It can only be following this time travel event in 2024 that a time traveller arrives in 1985.
Otherwise, you are just stipulating that time travel is impossible or that there was never a period without a time traveller from 1985 to 2024, which both amount to the same thing. If there was never a period without a time traveller from 1985 to 2024, then there was never a time travel event which transported the time traveller back from 2024 to 1985. The time traveller was just always there in 1985 and didn't - or didn't need to - time travel. No time machine required.
Quoting noAxioms
Why does the first time travel event allow history to "all get rewritten again" but the second time travel event does not?
Quoting noAxioms
How does he necessarily alter history to one in which he is never born?
Quoting noAxioms
How does the butterfly effect of the time travel event necessarily prevent the evolution of humanity?
Wow :gasp:
Quoting noAxioms
My own. Replying to your comment does the job.
What is exactly the 'exact matter' including various virtual particles?
Quoting noAxioms
So does it not prove that the whole story is just a fiction itself?
Quoting unintelligiblekai
The OP seems to have already taken into account of time travel is a fiction, but asked how it could be possible even hypothetically. Shouldn't how one could change the past events follow after fictitious successful time travel has been achieved, rather than before the travel? Have you achieved fictitious time travel into the past or future in actuality?
Isn't quantum teleportation essentially just the transfer of information though?
Not really. CTCs are allowed, and might actually exist at quantum scales. Their existence is not inherrently contradictory. To open one at a classical scale probably leads to necessary contradictions, and since all the time travel stories are classical, I'd have to actually answer that such stories are necessarily fiction.
You quote the OP asking this same thing:
Quoting unintelligiblekaiOne can scan a person down to the biochemical level: the location of every cell and connection, the chemical makeup of all fluids everywhere. That's still a classical measurement. It's trying to scan down to the atomic level where things get impossible.
I had also asked this question when I brought up the Studebaker back around post 55 or so. (I wish this site numbered its posts). SEP is strangely mute on this particular case, and it has quite a list. In the end, it 1) only works forward (but so do some of the other cases designated as time travel in SEP), and 2) it is arguably a copy, especially since the environmental circumstances can be positioned in multiple locations at once, something not possible with the teleportation I mentioned, which is otherwise arguably a similar thing, even down to the quantum scale.
I think to qualify as time travel, it would require some sort of getting to what appears to be a past state. So for instance, in my Disney example, we take a scan of a town in 1955. Then Disney, in 2055, makes a big box in which the town fits. They put a copy of the 1955 town in there, and let you in. The people inside don't know. They're not actors. Have I time-traveled? Have the townsfolk?
Quoting CorvusI cannot parse this. How does something follow something that is fictitious?
Quoting PantagruelGood question. Yes and no. Yes, the state of the source side was somehow reduced to what might be construed as information (something one might shove through a wormhole??), but not information that could be monitored or saved in any way. The ability to do that would violate Heisenberg's uncertainty. But whatever was 'transmitted' to the destination 'booth' (I don't know the actual words they use), it reproduced the state of the source exactly, which necessarily does not leave the source behind. It is entirely quantum, not a classical copy. If the particle was entangled with some other particle, it still is after the teleport. That would not be true of a copy.
Quoting LukeI think you used the word 'rewind'. It seemed to work like a VCR tape recording all of history everywere. Anytime somebody travels back, you rewind the tape to 1985, and start recording from there. If that's how it works, then the tape will never reach year 3000 because somebody (not always the same person) keeps rewinding it.
The original idea you pushed was the branching one. Whenever somebody goes back (and maybe forward, don't know), a new tape starts recording from the arrival event and the original tape keeps recording, which includes the time machine just vanishing permanently. You abandoned that model.
Anyway, if I got things wrong, you need to correct me on how the model actually works because I don't see how the tape can make forward progress if anybody anywhere has the power to rewind it arbitrarily far at any moment.
As for Back to the Future, that movie has holes. It isn't self consistent.
I didn't say otherwise. The VCR tape resumes recording at 1985 and progresses no problem.
Well, from about 1986 on, the people born will be different ones. That's a very chaotic function.
If this new timeline also has a time travel event in 2024, then the rewind happens again. If there is no time travel event there, then no rewind takes place then. That's why I came up with the 30 second train-track example, where the subsequent time travel decision is very likely. Over 40 years, it is very unlikely that events will turn out identically, especially if Bob goes back to 1985 explicitly to prevent the creation of the time machine.
What does rewind do to the 40 years over which we backtrack? It either erases as it goes or that part of history gets overwritten as the recording resumes. Either way it is not part of the universe. That's the problem of using the same tape to record something new: you lose what was on there before.
I didn't say that.
Who gets born is very much a function of exactly when people have sex, and which sperm wins. Which species come about is very much a function of random mutations and environmental chance. All these things are altered by chaotic things in the environment.
Read up on chaos theory. I can't possibly explain it to you in this context. There is no strange attractor for a specific person being born, or for a specific species to evolve. There would probably be mammals around since those existed in the Cretaceous, but probably no mammal that you'd recognize.
Yes, it must have been my mistyping. I try not to google too much if I can help it. The underlying implication for asking the question was not just the meaning of the concept, but also your explanation on how it works with time travel.
Quoting noAxioms
Not saying they are not allowed, but trying to focus more on the possibility of the travel before what one can do in the past or future when arrived there.
Quoting noAxioms
But there are loads of the other aspects that you must think of such as the mental contents = memories, thoughts and the consciousness of the past, such as if you travelled to 1761, would you still contain the present mind, or would the content of your mind be wiped out, and replaced by the 1761 mind, or would it become total blank due to the travel?
Quoting noAxioms
Fictitiously.
Not saying time travel is total baloney, but I am interested in how it might be possible, as well as what you could do in the past or future when you arrived there.
:up:
Quoting noAxioms
Yep, got the description for "exotic matter", but you still need to explain why and how exotic matter is required for time travel. How does it supposed to work?
Sensitive to initial conditions is easily understood as the butterfly effect, but the other two conditions (both of which may imply SIC) are not as easily digested when one attempts to apply chaos theory to the real world. The theory assumes a dynamical system, which means a simple iteration of a single complex function. And the iteration of points must follow stringent patterns. Bringing up CT is like bringing up QT.
Why would any of that occur? I mean, sure, if one was to travel to 1990, they'd find me there, but without 2024 memories, but why would the teleporter leave you in a different state when it by definition doesn't?
Given a physical monist philosophy of mind, one would presume the person to arrive with all memories, experiencing nowt but a sort of change of environment, very much like getting on and off an elevator.
Given a supernatural philosophy of mind, I suppose one has to address whether that part goes with you or not, and what happens to it if not, and if something replaces it if not. All that is similarly discussed in scenarios like the Star Trek transporter.
Given a closed time loop, there's absolutely no reason to worry about it since there is no 'moment of actual travel', no reason for one's consciousness to not follow along like it always has. Not my problem anyway, it's the problem of the dualist.
Take time dilation, which SEP says is time travel: Suppose I get in a fast ship that dilates me to 1000th of the usual rate. Physics says I would not notice, but the dualists with a model of a mind experiencing the objective flow of time, the experience would be that it would take an hour to draw a breath, something you'd likely not remember to do for an entire hour. The boredom and inability to function would kill you. The falsification test is safely behind a wall of technological capability. Nothing we have can test a human accelerated enough to empirically tell the difference, and the machines that have don't count since humans are special in this regard.
Quoting Corvus
Well, the usual physical explanations disallow the concept of 'change the past'. That means much of our discussion is moot. The machine (presuming unrealistically that the requirement is a vehicle of sorts) comes first, then the development of it. More realistic is the idea that the connection is established at both ends and there's no surprise when something appears uncaused 'from nowhere' so to speak.
Quoting Corvus
Ask those who have worked out valid solutions to Einstein's field equations. Apparently it cannot be done without utilizing negative energy and such. The Alcubierre drive (NASA reportedly working on it) requires it as well, at it very much would constitute time travel if it worked. All these require bending spacetime in a manner that isn't possible with ordinary positive energy. Neither of us knows the mathematics of it well enough to understand their explanations.
Tachyons for example need more (negative) energy to go slow than they do to go fast. They can approach c (from the >c side), but not reach
Quoting jgillThe simplest models exhibiting chaotic behavior may be simple, but real functions are anything but. The weather for instance is not a simple iteration of a single complex function, and yet it is very chaotic, and all that we've discussed (who gets conceived/born, which creatures evolve) is very much a function of the weather, among countless other factors, most notably wave function collapse.
I assume you are not talking about "real functions" as compared with "complex functions", but what we find in nature.
Quoting noAxioms
Huh. How did wave functions sneak in? But I'm being picky . . . please continue time travel speculation.
You used the word "rewind". I followed your usage to point out that time travel does involve a sort of rewinding of time. However, as I have repeatedly said, in addition to rewinding time, time travel also inserts something into the earlier destination time that wasn't there previously: a time traveller (and, perhaps, their time machine).
Quoting noAxioms
Not if we only discuss one time travel event, like I keep asking.
Quoting noAxioms
If we can stick to only one time travel event, then the model works like this: 1985 progresses without the appearance of any time traveller, until 2024 when someone first time travels and they arrive back in 1985. Everything about 1985 (the second time around) is almost the same as it was without the time traveller (the first time around), except that now it has a time traveller in it. In this way, it is very much like Back to the Future. The second time around with the inclusion of a time traveller, 1985 will likely proceed very similarly to how it did the first time around, except for whatever effects the time traveller has to change things from how they were the first time around. It is probable that most of the changes will be localised around the time traveller's location. Time will progress in its usual fashion, just as it did before the occurrence of the time travel event in 2024.
Quoting noAxioms
I'm happy to discuss the inconsistencies if you'd care to name them.
Quoting noAxioms
Exactly, except that 1985 now contains a time traveller, whereas it didn't before the "rewind".
Quoting noAxioms
I don't believe that it would be very chaotic, or that many of the people born would be different ones, unless the time traveller was very powerful and/or dangerous and was willing and able to make a lot of global change/damage. Anyhow, so what if it is very chaotic? The time travel event has occurred and makes sense.
Quoting noAxioms
I wouldn't expect events to turn out identically.
Besides, I thought your example was supposed to end the timeline somehow, but I still don't follow how it does.
The time travel event which occurs in 2024 and sends the time traveller back to 1985 is all a continuation of the same timeline from its beginning, albeit with a changed/changing history of events. But it should be expected that a time travel event changes the history of events, given that it involves inserting a time traveller into a time (the second time around) which didn't previously contain one (the first time around). An Eternalist might argue that there can be only one history of events, but I would argue that that singular history should contain all events that ever occur, including those of the first time around, without a time traveller, and those of the second time around, with one.
Quoting noAxioms
I've said that it gets overwritten.
Quoting noAxioms
I have read about chaos theory, thanks. Is there something in particular you could cite which would explain why it is necessarily the case that humanity could not evolve if a time traveller were to appear in the Cretaceous period?
If time is some physical entity running itself somewhere in the universe, and if there were different timelines running in different physical spaces, then perhaps you could get into the space via the teleport or whatever bending spacetime and what have you, maybe then you could say your mind and body of 2024 can travel to whatever year you choose without losing the memory, thoughts or consciousness.
But if time is just a mental concept for measuring the intervals between the start and end of changes of the objects in the physical world, then the whole topic would be just a fiction. Even if you accept whatever premises for time travel hypothetically and keep speculating what you would do in the past or future in time travel, you still have to accept the most foundational universal law, that all minds and bodies are subject to change through time.
Under the law that even God cannot intervene, your mind will be that of the people who lived in the world of whatever year you travel to, and you body as well. Perhaps your body will need a few deaths, resurrections and new births to reach the time you are supposed to travel to if it is a few hundred years away from the present moment.
Quoting Luke
So you seem to envision two dimensions of time. One is Earth coordinate time, as measured with numbers like 1990, moving horizontal to larger numbers, and the other is perpendicular, and moves 'up' with each travel event.
You seem to assert a single physical space that is 'overwritten', which is a lot like a VCR tape, except there are perhaps no spools to rewind since you seem to balk at that word.
So there is the tape which holds the entire history of the universe up to a 'present' where the write-head is writing. It writes up to 2024 say and then Bob goes back to 1990. A write head goes back to 1990 (without erasing, which would be truncation, another word you don't like) and starts overwriting there. It is unclear if this is a second write head (leaving the 2024 one to continue writing a universe without Bob, or if the history stops there and waits for the write head 34 years prior to catch up.
With this model, Bob goes back, and the history of the creation of the time machine in 2023 still exists, but the writing is going on in the 90's and when it finally gets to 2023, it overwrites the creation of the time machine, leaving a time machine without a creation event in any of history.
It of course exists in the timeline left behind (in the 'down' direction of the 2nd kind of time) described by the part you bolded above, but that line isn't the one actual timeline, it has been overwritten.
Did I get anything right this time, or is the model completely different than that?
There are implications, but if I got the model wrong, there's no point in discussing them.
So you want to limit the discussion by imposing a single travel event restriction. This would prevent us from exploring the plausibility of the model. Apparently avoiding that exploration is something you want.;
Let's discuss Alice and the train tracks then. That's one 30-second travel event, sort of. I don't know how to analyze that since I don't know if I got your model right.
A description that works only in one case isn't a model.
You seem only to describe the traveler, not what it's like to be left behind, to be 'overwritten'. Back to the Future (BttF) never shows what it's like for his loser parents to be overwritten by the confident parents. These are the parts missing from your model.
For a brief time, maybe. BttF seems to adopt an unrealistic fatalistic approach without chaos theory. It's entertainment and isn't supposed to be consistent with physics.
You can hold this belief all you want, but the mathematics says otherwise. Things turning out the same way assumes a very hard variant of determinism, even without the appearance of something that can't be there.
Why is it important to hold this belief? I don't see the problem with history unfolding a completely different way after a while.
On the vertical time axis, yes, as described above. But that sort of runs into problems when there is more than one travel event, an avenue you seem reluctant to face.
I don't know your model clearly. I can't discuss this.
Evolution of specifically humans was less likely that a 1 in a gazillion chance. Countless uncaused random events needed to happen just so. So the odds of rolling the same gazillion sided die and getting the same number is effectively nil.
Yep, and we're changing the environment, and also letting all the random events have a 2nd try, and they'd all have to come out the same..
Quoting CorvusNot really clear what might be meant by that...
That sounds like a multiverse of sorts, levels I-III if that means anything to you. But the whole point of them being a multiverse is that the states in the various physical spaces don't interact. If they do, it's one universe, not multiple.
OK, you seem to separate mind from the physical state, so it's on you to figure out how the two might keep track of each other.
But if time is just a mental concept for measuring the intervals between the start and end of changes of the objects in the physical world, then the whole topic would be just a fiction.[/quote]This sounds like the idealism hand-wave. We interact with anything (an object say) via mental concepts. There is no other interface. If you want to draw the line there and say that the physical state corresponding to that ideal supervenes on the ideal, then the story stops there. And BTW, 'object' is very much just an ideal. There seem to be anything physical about what constitutes an object.
I'm getting pretty far off topic here.
We seem to have gone off on a supernatural tangent. Not my problem.
Quoting jgillUm, yes. I'm talking about the complicated functions of reality as opposed to the simple functions often used to demonstrate chaotic behavior in textbooks.
Quantum randomness is a critical part of especially mutations. Given a different starting state (or even the same starting 'state' but without hard determinism), a completely different outcome will collapse out of the wave function of all possible futures of that initial state.
It is just one of the different scenarios of what the nature of time might be.
Quoting noAxioms
That wasn't anything to do with a supernatural tangent. It was just an expression to emphasise that you cannot reverse time, and no one in the whole universe can. No one said that was your problem.
Quoting noAxioms
You have been for sure. OK, please carry on. I am bowing out here.
No.
Quoting noAxioms
I don't know what you mean by horizontal and perpendicular dimensions.
Quoting noAxioms
The time traveller originally passes through 1990 without any time travel events (as a child, say). They subsequently grow up and build a time machine. Subsequent to this, in 2024, they travel back to 1990 (as an adult time traveller). There is no time traveller (who has time travelled) in 1990 until after the 2024 time travel event. 1990 is only "overwritten" (post-time travel) in the sense that it now contains a time traveller, whereas it did not contain one before the 2024 time travel event. It is also "overwritten" in the sense of whatever effects the time traveller has on the timeline from 1990 onwards post-time travel that they did not have on the timeline from 1990 to 2024 pre-time travel.
Quoting noAxioms
I have no issue with the word 'truncated'. You claimed that the timeline could be permanently truncated. I still don't follow how or why that could be.
Quoting noAxioms
Since the timeline gets overwritten, whatever effects Bob has on the timeline from 1990 onwards (post-time travel) will ripple through to 2024. The people and history of events in 2024 pre-time travel are affected by Bob's actions from 1990 onwards (post-time travel). Some people who are at 2024 after Bob departs in his time machine may simply disappear from the timeline thereafter, like family members in Marty McFly's photograph. Whatever effects time traveller Bob has on 2024 will only be witnessed when 2024 comes around again. However, we can consider the post-time travel effects from the 2024 perspective without waiting for 2024 to be present again. That is, I'm not suggesting that 1990 and 2024 are both progressing simultaneously. After all, I'm not an Eternalist.
Quoting noAxioms
The history of the time machine is that it was built circa 2024 pre-time travel, it then time travelled to 1990 and continues to exist thereafter. It is a similar history for the time traveller. The important fact is that 1990 post-time travel is necessarily continuous with, and subsequent to (can occur only after), the time travel event in 2024.
Quoting noAxioms
I'm asking that we get clear about a single time travel event first.
This is just a repeat of what was said before, without answering any of the questions. It's always described only from the PoV of Bob.
Bob is born 1985, meets Sue in 2002, married in 2007, and has a daughter Roberta, born in 2010. Bob kills young-Bob in 1990, so what is the experience of Roberta when she gets overwritten? What is the experience of Sue when she still exists, but has her marriage and all her history overwritten?
Apparently nobody can witness the departure event of the time machine, at least not if it goes backwards. You've given no clue how it can go forward to some piece of history that has yet to be written.
You balked at that before. So no overwrite, but just truncation, and a new building onto 1990, not overwriting some alternate future that no longer will happen. Robert is immediately gone, and never was, and never will be, in the world timeline which is presently at 1990. The time machine now exists without having been created since its creation has been truncated off. It doesn't exist and never will. You seem to not like that, but that part doesn't bother me. Sure, its creation exists on Bob's line, but most of Bob's line is not part of the universe, but just a memory.
The train track scenario illustrated that, but it depends on your answers. The truncation interpretation does result in that, yes. Time cannot move forward. The machine has God-like powers and can actually take control of where the present is and put it somewhere else. Any alien with this technology can effortlessly wipe out human existence simply by truncating us off of history.
This is why I don't like the truncating interpretation. Too much power for a simple machine. The rewind/overwrite interpretation has the same problem. Not all interpretations do.
Eternalism suggests no such thing. There is nothing that 'progresses' at all.
OK, the train track thing is a single event (sort of), and I don't see how the universe can ever get to tomorrow with it.
At time 12:00:25, the train gates go down. At 12:00:30, Alice gets to the crossing, who's in a hurry and she's driving the DeLorean. She hits the button to go back 30 seconds.
At noon, a DeLorean appears at the tracks and proceeds across. 400 meters back, a DeLorean approaches the crossing.
At time 12:00:25, the train gates go down. At 12:00:30, Alice gets to the crossing. She hits the button to go back 30 seconds. The Alice on the other side of the crossing is truncated out of existence.
At noon a DeLorean appears at the tracks, almost exactly in the same place as the other one that appears there. OK, so there is some sort of resolution of a car appearing at the location of a car already there, so either there is an explosion and the Alices all die (yay for the universe), or one wins and truncates the other out of existence, and the cycle continues.
I have to admit that there is a solution to the problem that I didn't see before.
Your responses indicated that you were unsure of my concept of time and time travel. I was attempting to clarify it for you.
Quoting noAxioms
Roberta won't have any experience if she is overwritten, because she will cease to exist. As I said in my last post, some people "may simply disappear from the timeline" as a result of time traveller Bob's actions post-time travel.
Quoting noAxioms
It will be whatever her experience is in the post-time travel timeline. I'm not sure what sort of answer you are seeking. Since older Bob (the time traveller) has killed his younger self, then Sue won't meet young Bob or have children with him.
Quoting noAxioms
Someone could see it disappear, I suppose, but yes, basically.
Quoting noAxioms
Because I asked early on in the discussion for us to get clear on one backwards time travel event first.
Quoting noAxioms
I wasn't sure what you meant by it before. I still don't believe that the timeline gets truncated or shortened permanently.
Quoting noAxioms
If this is your interpretation of my view, then it's incorrect. I said that the timeline gets overwritten, but you've somehow interpreted that (to be the opposite of what I said) as "no overwrite, but just truncation".
You are correct that the pre-time travel period of 1990-2024 "no longer will happen", but only because it already did happen. That pre-time travel 1990-2024 period which did happen gets overwritten by the post-time travel history from 1990 onwards that happens subsequent to it.
Quoting noAxioms
I assume you mean Roberta, and yes, this is all true once the time traveller kills young Bob.
Quoting noAxioms
The time machine was created pre-time travel, circa 2024. I think you mean that it won't be created again on the post-time travel timeline (exactly as it was created originally by young Bob on the pre-time travel timeline). This is true. However, it definitely does exist in 1990 post-time travel. Why wouldn't it? It transported the time traveller to 1990 from 2024. It will continue to exist (post-time travel) until its destruction.
Quoting noAxioms
Okay then, it's just a memory. My argument is that time travel and the act of time travelling to kill one's own grandfather (or their younger self) is hypothetically possible and logically consistent. I don't really need to maintain the existence of the pre-time travel timeline for that purpose. Although I understand why an Eternalist would prefer for that section of the timeline to remain in existence.
Quoting noAxioms
That isn't truncating the timeline; it's truncating human existence. Time continues to "move forward" with or without us.
Quoting noAxioms
Doesn't this imply that nothing ever happens in an Eternalist universe? Therefore, there is no such thing as travel? That would be a different type of grandfather "paradox".
Quoting noAxioms
It sounds like this truncates Alice's existence, but I don't see how it permanently truncates the timeline.
Quoting noAxioms
Did you mention the solution already or are you keeping it to yourself?
Quoting LukeThis seems contradictory.
Robert and Sue are watching Bob get into the time machine. He reaches for the button and Roberta ceases to exist and Sue is currently a child with zero memory of 2024. That makes the departure pretty much impossible to witness.
Overwrite means the time between 1990 and 2024 still existrs, but gets changed as time makes its way across that period. Truncation means it is gone, and the new write is added to the end of existing history, which is at 1990. The two are the same after 2024 is reached again, or until there is another travel event.
You have a funny definition of 'did happen'. Those are future events, and if it's 1990, they're not in the past and thus the use of past tense is misleading.
This is what I mean by you referencing two dimensions of time. One is the time I'm talking about, where 1990 comes before 2024, and the other is the time containing the first kind of time. So you can lay out a graph with two time axes, and graph where the present is (y axis, calendar time) for a given 2nd kind of time (x axis, Luke time), which would show a steady line up to 2024 where it jumps to 1990 and continues upward again. Two dimensions of time, and it being a simple exercise to plot out all the jumps this way.
I tried linking an image I drew, but the site apparently doesn't support images. Click the link.
Along the x axis, the present is at 1990 more than once, and the 2nd 1990 happens after the first 2024, but all of it 'happens' at some point. That corresponds more to no time travel at all, and history isn't deleted at all, but rather the state of the universe is simply reset to a prior state the exception of the contents of the machine which are protected from the overwrite everywhere else. If it does that, then yes, the pre-time travel period of 1990-2024 did very much happen since that 2024 is in the past of the second 1990. That is sort of an 'append' view where nothing gets deleted. Roberta still exists (the thick maroon part), but her worldline ends abruptly when the universe is rewritten to a state that doesn't include her. The time travel machine thus would have access to any of those states (such as pre-travel 1996) and could reset the universe to that state if those coordinates are chosen. They still exist, so you could 'go there'.
Interesting side effect. You're at a time travel convention, and 20 of you with similar machines all decide to eat at Joe's in 1936 where the food is cheap. Only one machine (the first to leave) makes it, the rest are erased from history before they can follow.
I think, but am not sure, than when you get in you machine and set the coordinates for some destination, that you select a value on the y axis and not on the x axis, but it isn't really clear. One cannot fully understand your view unless forward travel is described. Sticking to this one-backward-jump case leaves several open questions.
I grant that. It has universe-ending consequences, but the grandfather thing isn't itself paradoxical in this view. Presentism does buy you that. The paradox has more teeth when you take presentism away.
Things don't 'remain' or 'go in or out of' existence under eternalism. You seem to not understand the view.
The train example may or may not permanently end time for the entire universe, depending on answers to questions concerning how subsequent jumps are handled.
No. The Titanic sinks in 1912. Humanity goes extinct in 2316. Those are eternalist statements since they contain no references to the present. Events still occur at specifiable times, which is what 'happens' means.
Ted is home at 7AM, Ted is at school at noon. Ted must travel to be at different places at different times.
Time travel under eternalism would be illustrated by a picture showing the state of things at each time. There would hopefully be but the one dimension, so 1990 is before 2024 unconditionally. There is no 'first 1990 and second 1990'. That opens the door to the paradoxes, but it also allows a time machine to exist uncreated. Your view I think doesn't support that.
...so either there is an explosion and the Alices all die (yay for the universe), or one wins and truncates the other out of existence, and the cycle continues.
— noAxioms
It sounds like this truncates Alice's existence, but I don't see how it permanently truncates the timeline.
[/quote]Whether it permanetly truncates the history of the universe depends on what Alice does as she approaches the tracks. If there is a massive wreck of DeLoreans at the crossing, she might be reluctant to hit the end-universe button, and will simply miss her appointment. That's the way out of the pickle. She (the Alice who has never time traveled yet) needs to make a different decision based on what the future Alices have chosen to do. I've given her only 30 seconds to realize that, but I think it's enough.
The question is unresolved until you clarify how subsequent time travels work,. In particular, what happens to the object at the location where the machine 'appears'? Does it murder the person there? Does it look for a relatively harmles place to appear? What if a million machines all try to go to the same spot? Eventually space will run out for them all, and Earth collapses into a black hole from too many DeLoreans.
Work through the Alice example. I didn't keep it to myself.
Okay, maybe you're right. Nobody can witness the departure of the time machine.
Quoting noAxioms
I don't see that there's much difference between 'overwrite' and 'truncation'. Post-time travel, on the truncate model, the history of events from 1990 to 2024 is deleted and the resulting blank period from 1990-2024 gets overwritten by a different history of events. On the overwrite model, the history of events from 1990-2024 is retained but gets overwritten by a different history of events. It makes little difference post-time travel.
Quoting noAxioms
The time machine's departure from 2024 did happen before its arrival in 1990. Otherwise, you are simply prohibiting the possibility of time travel by stipulating that all events - and all use of tensed language - must obey date order.
Quoting noAxioms
If I understand you correctly, the two dimensions of time are date order/calendar time and "the time containing the first kind of time". It's not clear to me what you're referring to by "the time containing the first kind of time".
Quoting noAxioms
It would be reset to a prior state if not for the additional insertion and subsequent effects of the time traveller and their time machine into that earlier time.
And how does the graph look if the (1990-2024) history is deleted/overwritten by the new timeline? Because that's what I'm saying.
Quoting noAxioms
If you accept that history gets overwritten, then I think there would be only one axis/timeline.
Quoting noAxioms
Forwards time travel is just like backwards time travel. The timeline that would have existed if there had been no time travel events gets overwritten (from the time machine's arrival date onwards) by a new timeline which includes a time travel event and its effects.
Quoting noAxioms
I know that things don't remain or go in or out of existence under eternalism. That's why I said that an Eternalist would prefer for the overwritten section to remain in existence; because its going out of existence is at odds with eternalism.
Quoting noAxioms
I'm aware that the words "happen" and "occur" are usually synonymous, but it's unclear what it means for an event to "happen" or to "occur" on an Eternalist timeline, especially since, as you say, "there is nothing that 'progresses' at all." Do the terms "happen" and "occur" mean anything other than that the event exists?
If Eternalists take "exist" to be synonymous with "happen" then, since Eternalist events do not cease to exist, they must also not cease to happen. There is no past tense of events having existed or having happened for the Eternalist. This implies that, instead of the usual sequential progression of events wherein later events occur after earlier events, on an Eternalist timeline all events are happening en masse at their respective times and each event happens repeatedly. Just as Eternalist events do not cease to exist, they also do not begin to exist, and therefore they also do not begin to happen; they have no beginning or end. Like all events on the Eternalist timeline, the sinking of the Titanic in 1912 and humanity's extinction event in 2316 are both always happening, and they are happening over and over again (at their respective times). Or, it may not be the period of each event (of a different duration) that repeats; it could be more regular periods such as minutes or seconds that repeat. Otherwise, nothing happens on an Eternalist timeline and everything simply exists.
Quoting noAxioms
Travel is something which happens or occurs, and the word "travel" usually means there is something which progresses (in this case, Ted) from one place to another. Yet, you say "there is nothing which 'progresses' at all."
Quoting noAxioms
Since the pre-time travel timeline gets overwritten by the post-time travel timeline, then the time machine's creation would be overwritten. My view supports that.
Quoting noAxioms
Even with the black hole option - which I'm not ruling out - I don't see that time travel is impossible or logically inconsistent. So I don't see that it really matters whether I say that the time travelling cars can all occupy the same space or not. Black holes exist in our universe and they haven't ended the timeline.
As I said, you seem to order events per the x axis, and I tend to order events along the y axis. I presume you saw my picture. You will note the absence of numbers along the x axis since it was unclear what to put there. One could put Bob's age there, but that would only work if Bob takes part in every time jump ever.
No. You need the 2nd line to order all the different times that a given year appears. My graph shows that, and all you posts reference this x-axis kind of time. Machine gets created. After that, machine gets used. After that, creation of machine gets overwritten. All nice and causal.
It can't be. There is no future, since it needs writing first. The machine would, at minimum, be forced to wait for the destination to come around, holding its occupant in stasis all the while similar to cryonics but without the cold.
Why would you want that? There seems to be no point.
If the line continues as if no travel event occurred, the Roberta (age 14) watches Bob push the button for destination 2035. You say the timeline continues as if the travel event had not occurred, so Roberta keeps her dad, who appears to be a failure. We call him F-Bob. Meanwhile Bob is actually successful, and is traveling to 2035. We call him S-Bob (success). 2035 goes by for some reason and S-Bob doesn't show up. A long time goes by (you don't say how far it goes) and suddenly S-Bob appears in 2035, truncating history back to that point, and F-Bob's 50th birthday party, who says "Who the f*** is that? I thought it didn't work!". 39-year old S-Bob replies "It sure as s*** worked!". Yes, F-Bob drops the F-bomb and S-Bob drops the S-bomb. Sorry, couldn't resist that one.
Anyway, the usual description says that 'history' proceeds as if Bob had actually traveled, and Bob is not in 2025 at all, and Roberta doesn't see him again until 2035 when he shows up out of thin air. History is not in need of truncation at all since it just then got to that point.
All that said, if you agree to the latter, we can demonstrate issues that result. The way you word it makes it into a cloning machine. You can make an army of soldiers in minutes using such a machine, just by setting it for one second from now.
Are we going to discuss the contradictions that might arise by having Bob (or others) make more than just the one jump? It all works great and intuitive for a single jump, but the differences in the interpretations really comes out when everybody has one.
I also notice that you've dropped the discussion of Alice at the tracks, ending the universe. That was one consequence of the truncate interpretation: a universe that cannot progress.
No, there can be no overwriting or anything. There is no writing at all. There is but the one timeline (or more if you want), but they don't change. Change is something applicable to something contained by time.
An event 'happens' at the location of the event. Not sure how else to say it. The time coordinate assigned to the event might be frame dependent, but the event itself is objective.
I think not. I mean, by calling it an event, an implication is made that the event exists at a point in spacetime, and all points in spacetime have a location on the time dimension, just like they have a location in the spatial dimensions.
No, that's not true. The length of my table might exist, but it's not something that 'happens'. It was the word 'event' that carries an implication of being part of spacetime, and that, coupled with a premise that spacetime exists, implies that an event exists.
Not sure what 'cease to happen' means, but events, by definition, 'happen' somewhere. They would perhaps be said to exist in the spacetime of which they are part.
Agree
Ouch. No! There is no repeat. They happen once. An event cannot have multiple temporal locations. An except to this is the usage of a coordinate system that does not exhibit a 1-1 correspondence of events to coordinates. Under such coordinate systems (such as a variable acceleration one), events can have multiple valid sets of coordinate values, and thus 'happen' more than once, and in more than one location. One of the best illustrations of this is the Andromeda paradox, which leverages such a coordinate system.
Events can be ordered. One can say that event A happens before event B. If the two events are not spacelike separated, then that ordering is objective. If the events are spacelike separated, then their ordering is frame dependent,. per relativity of simultaneity.
Point is, there is still a sequence for the sort of events you're imagining: Titanic sinks before WWII.
What eternalism lacks is the premise of a 'present' moment, objectively separating all events to three ontological states of 'past, present, and future'.. Any reference to the thing not posited is meaningless under eternalism. Hence the lack of tensed verbs, since such verbs carry a reference to the thing not posited.
I am not sure how you distinguish the terms 'happen' from 'begin to happen', but events do happen. A process that has duration (a house fire say) is something that begins to happen, but an event, being a point in spacetime, has no duration.
No. 'Is happening' is a reference to the present. Please don't make up your own ideas for eternalism. There is no repeat to it.
Different usage of the same word. Yes, Ted's life is a progression from his early times (conception) to his death. All those events exist. They all happen. They are ordered, so in that sense, there is a progression. There is no special event which is 'current', which moves along his worldline. In that sense of the word, there is no progression.
Not sure what black holes have to do with our timelines. I don't anticipate either of our lines being in a black hole.
And no, there are unfalsified theories that don't allow black holes, so their existence is not fact, but the consensus is that the one theory that predicts them has been dang successful, so their existence is presumed.
I fail to see how your examples of multiple time travel events end the timeline. I only see that they end the existence of humanity, which is not the same. With truncation or overwrite, time still marches on.
Quoting noAxioms
Where on your graph does it show that the timeline is overwritten from 1990 onwards and that the pre-time travel 1990-2024 period ceases to exist?
Quoting noAxioms
No. A given year appears on the graph only once but that same year can be overwritten. Since events are overwritten, the same graph line returns to 1990 and starts (writing) again. This is virtually the same as if the timeline were truncated back to 1990. There is no 2nd new line. The time machine's creation event and departure from 2024 get deleted/overwritten in the history of events. Your graph shows a timeline that is not overwritten, but I'm saying that it is.
Quoting noAxioms
I never said that future events must actually happen before there can be time travel to a future time. I said:
Quoting noAxioms
I don't really want that; it's just how forward time travel makes sense to me. We can imagine a timeline of future events; of how things could/would have been if there were no time travel events. This imaginary future timeline is what gets overwritten by a time travel event. This is similar to backwards time travel, except that backwards time travel has an actual history of events (without time travel) that gets overwritten by a time travel event. It's not really any different because in either case the time travel event overwrites what the timeline was/would have been.
Quoting noAxioms
I don't believe I have ignored it. You said the result would be a bunch of cars all arriving in the same location causing a black hole. This does not explain how the timeline ends. Otherwise, I do not understand how the timeline is supposed to end in your Alice example. As I said earlier, your examples all indicate the end of humanity's progression but I don't follow how they indicate the end of the timeline's progression.
Quoting noAxioms
You seem to have lost track of the discussion. I never suggested that eternalism involves overwriting or writing. We were talking about my time travel example, which does involve overwriting the timeline. I said - in relation to my time travel example - that I understand that an eternalist would prefer for the overwritten section to remain in existence, precisely because eternalism does not involve change or things going out of existence.
Quoting noAxioms
That's not very helpful. I'm asking you what it means.
Quoting noAxioms
Okay, then the terms "happen" and "occur" are synonymous with the word "exist" (at least, in relation to events).
Quoting noAxioms
I find it odd that you refer to an event as occurring at a single point in time. I suppose the word could be used in this way, but I typically think of events as having a duration; lasting for a period of time. [I note that you later go on to distinguish an event from a process, but my responses are in terms of a process, not an event (in your terminology).]
Quoting noAxioms
You've just told me that the terms "happen" and "occur" do not mean anything other than that the event exists. Now you're saying those terms do mean something other than that the event exists? "Happen" and "occur" are not synonymous with the word "exist"?
Also, since eternalists treat time as a spatial dimension, then why wouldn't they say that the length of your table happens, just like the length of an event (i.e. a process) happens? What's the difference?
Quoting noAxioms
As I said, I had in mind events with a duration of more than a point in time (i.e. processes). Those events (i.e. processes) have a beginning and end point. An event (i.e. process) is conventionally considered to end at the end point of the duration of the event. However, if eternalist events do not cease to exist (as eternalism claims), and if "exist" and "happen" are synonymous under eternalism (at least, in relation to events), then eternalist events do not cease to happen; they never stop happening.
Quoting noAxioms
I never said an event "has multiple temporal locations". I said "all events are happening en masse [/i]at their respective times[i]."
Quoting noAxioms
Sure, eternalism can allow for a sequence of events, but what does it mean for those events to happen?
Quoting noAxioms
Ah okay, I see now that I've been using the term "event" to refer to what you call a "process". I will adopt your terminology henceforth. I note that a process requires progress. Incidentally, I would have thought that the sinking of the Titanic was a process rather than an event.
Quoting noAxioms
Right. I'm suggesting that, in order to say that all events exist/happen under eternalism, then all times must be, in a sense, present. All events exist and happen at each of their respective times. Since they all exist and happen at all times, I don't follow why they should happen in a sequence from earlier to later, so that they apparently happen one after another. This suggests that there is a "special event which is 'current', which moves along [the] worldline," which sounds very much like a progression. Instead, eternalism entails that events all happen en masse at their respective times, rather than in a sequence, one after another. But in that case, each event must happen repeatedly, without beginning or end.
Quoting noAxioms
I don't see two different usages of the same word ("progression"). Please define the two different usages/meanings.
Quoting noAxioms
This was part of your Alice example, which is what I replied to, in which a black hole resulted from the Deloreans all arriving at the same location.
We've not considered multiple travel events hardly at all, so I'm not sure if the consistency of a particular interpretation will ever be explored.
March it does, but in the example I gave, it just paces back and forth. That needs to be resolved I think before we consider multiple machines.
One can shade all the regions below the line. Those are events that exist (history that is written) at a given time on the x axis. One cannot ask what the state of 1990 is (a time on the y axis) because it has multiple states, being written more than once.
Neither did I. Bob is traveling to it, but it must happen first before he can arrive, else he ends up in a blank universe not yet written. It would presumably be subjectively instant to Bob, just like it is backwards.
It makes sense to leave a copy of Bob behind? No time-travel fiction portrays it that way. Doesn't make it wrong, but it makes it into a cloning machine. The army would love it. Millions of somewhat disposable trained soldiers at the push of some buttons.
We can imagine a timeline of future events; of how things could/would have been if there were no time travel events. This imaginary future timeline is what gets overwritten by a time travel event. This is similar to backwards time travel, except that backwards time travel has an actual history of events (without time travel) that gets overwritten by a time travel event. It's not really any different because in either case the time travel event overwrites what the timeline was/would have been.
The typical depiction is that the machine disappears, which results in the writing of history as if the travel had actually happened. If it doesn't happen, the car/machine doesn't disappear.
That's sort of one outcome depending on the answers to questions I've asked: What happens when multiple travel events target the exact same space and time? In my example, they're all the same travel event, but happening repeatedly in a different sort of loop that causes collisions. There can be an odometer this time, but outside the machine, not inside.
Then comment on the example. Where does my description of it go wrong? All I have is 'I don't get it'. I need to know what part you don't get.
I spelled it out in considerable detail a couple posts ago. No comments on that.
Not sure how to word it differently. The Titanic sinks on some 1912 night. That is a statement of something that happens. Relative to the night before, it has not yet sunk, and the night after, it is at the bottom of the ocean. Somewhere between those two events does the sinking 'happen'. It's not much different than presentism except there is no preferred moment that has to somehow glide across that event in order for the event to cycle through the different ontological states of 'happening' and then 'happened'. All events have equal ontology. Besides that, there is very little difference with the standard definition of 'happens'.
That was a bad answer. I think the two words mean essentially the same thing as each other, but you didn't ask that. You asked if the words mean 'exist'. No, the words do not mean 'exist'. The laws of physics might be said to exist, but they're not something that 'happen' or 'occur'. There's not a place at which the laws of physics specifically occur.
I also gave the example of the table length as something that exists, but doesn't 'happen'.
No, at a point in spacetime. Time is 1 dimensinal, but spacetime is 4D. An event is a point in 4D spacetime, just like a location is a point in 3D space. The latter, plus a moment in time, are all frame dependent things. Events are invariant: They're not dependent on a frame choice.
That's the colloquial definition. I'm talking about the physics definition. Yes, an event can be bigger than a point. The sinking of the Titanic took place over a kilometers and a few hours, but from a distance, that's a point, just like Earth is treated as a massless spatial point in something like the twins paradox.
I did. I misread the question.
Dimension yes, but it is a temporal one. One can still translate seconds to meters if you want. The units are interchangeable under the constant c.
I suppose you can say the table 'happens'. Mine is of size 40 years and its current length started 'happening' perhaps 34 years ago, and counting, all depending on how one chooses to measure its length of course. But when I speak of an event, I'm usually talking about something that is best treated as a point.
You said events happen repeatedly.
OK. I'm unclear on the distinction between all the events happening at their respective times, and them all happening en masse at their respective times. The latter wording would seem to be opposed to some of the events happening at their respective times, but other not.
OK. A fire begins to happen, and goes out at a later time, both ends being different events, with the fire being the process between. And yes, if you use 'event' to describe something with duration, like a concert, then it obviously begins to happen and later ceases to happen.
Horrible word choice, but I suppose so. That is not to say that they all exist at a present time, but 'present' in the sense of 'present and accounted for'.
They don't happen at all times. Each event has a time coordinate and only happens at that time.
That's just causality doing its thing. Classically, a later state is a function of prior states,. That works in both directions, but there is the arrow of time which indicates which way is forward.
So I can throw you a pile of pictures of the Titanic, and you could very likely put then in order, despite none of the pictures being the cause of any other.
Nothing of the sort is suggested. That is an additional premise, for which zero evidence exists. There's no empirical test for it (or, similar to the teapot orbiting past Jupiter, for its absence). Both sides have proposed all sorts of attempts at arguments for their side, but most arguments don't revolve around anything empirical.
The integers are ordered, but there is similarly no obvious integer which is the preferred one, despite each integer perhaps thinking it is the preferred one. The integers are ordered, but do not constitute a progression.
Again, you drag repetition into a view that implies no such thing.
Oh right... It was one of the solutions to the problem of the universe being unable to progress. Time travel (without the wormhole) violates mass conservation, but we're ignoring physics violations, so there is no limit to how many machines we can put in one place. Too much mass results not so much a black hole, but rather enough gravity to kill Alice and put a stop to what she's doing. The whole point of the train track exercise is to figure out how to get Alice out of the loop.
What I said is that I fail to see how it ends the timeline. You seem to refuse to comment on that. Your examples show only that my concept of time travel could have terrible side effects, such as the end of humanity or the possibility of cloning an army, which I don't see as being relevant to whether or not my concept of time travel is logically consistent. Even if your examples were to show that the timeline does end, this would obviously be disastrous, but it would not prove my concept of time travel to be impossible.
Quoting noAxioms
It paces back and forth only for as long as Alice continues to hit the button to go back every 30 seconds. As far as I can tell, nothing forces her to keep hitting the button.
Quoting noAxioms
1990 does not have multiple states, because it is either overwritten or it is not.
Quoting noAxioms
I'm quite sure you did, because it's exactly what you proceeded to say:
Quoting noAxioms
I never said that the future timeline is "a blank universe not yet written." I referred to the future timeline that would have existed if there had been no time travel events.
Quoting noAxioms
Why would it leave a copy of Bob behind?
Quoting noAxioms
The machine disappears. You did not explain why it shouldn't.
Quoting noAxioms
Yes, if the car/person jumps to the same location as another car/person then they would all die/explode/cause a black hole/etc.
Quoting noAxioms
I think I understand the scenario. What I don't get is how/why the timeline ends as a result.
Quoting noAxioms
To 'sink' typically denotes a process wherein an object descends from the top to the bottom of a body of water or a liquid. It could be argued that, while the event is happening, it is cycling through successive ontological states with each successive state being the "preferred" moment. This "preferred" moment is the state that is happening, as opposed to those that have happened or have not yet happened. As you note, this sounds a lot like presentism. You are apparently saying that in order for an event to happen, it must be present. However, I note that this is inconsistent with your earlier agreement to my statement that, "There is no past tense of events having existed or having happened for the Eternalist."
Quoting noAxioms
I said an event would happen repeatedly at the [its] same temporal location.
Quoting noAxioms
I don't think there's any difference. I was only aiming for more emphasis and clarity with 'en masse'.
I was trying to say that, if an event exists then it is happening. Since eternalists hold that events exist at all times, then they must also happen at all times, without the pesky requirement that they only happen when they are present. Therefore, all events are always happening - en masse, at once? - at each of their respective times, rather than them happening only when they are present. That's why they must also be repeatedly happening at each their respective times. Otherwise, the Titanic would have sunk before 1912 became present. The sinking of the Titanic event/process, with a short duration of a day or two, would have stopped happening way before 1912 if it were not repeatedly happening.
BTW, this is my argument ad absurdum against events happening in an eternalist universe, not what I think actually...happens.
Quoting noAxioms
So an event needs to be present in order to happen? Or can past and future events be happening (now) even if they are not present, given that those non-present events presently exist at their respective temporal locations?
Quoting noAxioms
You suggested it with your Titanic example:
Quoting noAxioms
The "preferred" moment is the state that is happening, as opposed to those that have happened or have not yet happened.
Quoting noAxioms
She simply doesn't press the time travel button again.
She's in a state where she's going to hit the button in 30 seconds. She's enough in that state that she does it. The question is, what's different about the nth time around that she doesn't, given the same initial state? There's not time for chaos theory to do its thing. Events 30 seconds from now are essentially determined, except for this machine appearing not quite in the sight of Alice who's going to hit the button in 30 seconds.
What changes, that she makes a different decision than the one we know she makes, for reasons specified?
OK, I presume they must. If they've not happened, wouldn't Bob appear in a blank universe, at a time where nothing had yet been written? The machine moves the present to a universe state that is nonexistent, leaving a universe with only Bob and his machine in it. It would make sense (and match all the fictions) if the machine waited for the writing of the target destination before appearing there.
It takes 11 years to write that future state (assuming an 11 year jump. It also clones Bob. Sure, from the traveler's viewpoint (the only one you ever consider), it looks like he just appears there, in 2035 with F-Bob sitting there much in the same way that none of the fictions depict.
You said that it goes to a "future timeline that would have existed if there had been no time travel events". If there had been no travel events, Bob would still be in the timeline instead of the machine, so aging F-Bob (the one that is not in the machine) is a copy of the not-aging S-Bob in the machine.
So if you have a machine that holds a thousand passengers, and set it to go 1 second into the future, you now have 1000 cloned people. Hence the soldier factory.
Of course you could always have done the same trick with travel 1 second to the past, with precautions, so the clone-making property of the machine was always there.
It disappearing would not be consistent with a timeline where 'there had been no time travel event'.
No, not under eternalism. There is no preferred moment in it. You know that, yet you persist with comments like that.
Because the comment IS presentist.
Your words, not mine. I would never have used the word 'present' (as in not-absent) in that way, in that context.
True (and meaningful only) under presentism.
No, they don't say that. Each event exists at a specific time, and not at the others. The comment is analogous to saying Paris and London exist in all places, and not distinct ones.
Really, learn the view before you start asserting what it must say. It hurts, the way you're murdering a view with which you obviously don't hold. It's not absurd at all when one accepts only its premises and not premises borrowed from an incompatible view.
My eternalism titanic example comments never say anything 'is happening'. That is a reference to a present that the view denies.
She simply decides not to hit the button again. You didn't provide any information in your scenario about why she time travels. Presumably she does it to avoid being hit by an oncoming train. Maybe she realises she can't keep looping back every 30 seconds forever and tries something different instead. Maybe she tries jumping from the car. Maybe she resigns to her fate.
Quoting noAxioms
What fictions involve time travelling to a future time where nothing exists; a "blank universe"? What fictions involve waiting for the future to happen first, before time travelling to it?
It would be a pointless time machine if the user had to wait for the future to happen before one could time travel to it. You don't need a time machine in order to wait for the future to happen.
Quoting noAxioms
Time traveller Bob departs the current time to arrive 11 years in the future. He does not stay behind.
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The only cloning that happens is if Bob travels to some time within his own lifetime and, even then, you would probably consider it cloning only if his time travel departure and arrival times were very close to each other, e.g. if he time travelled to 5 minutes ago or a day forward. I wouldn't really consider an 11-year younger or older version of Bob to be a clone or a copy of Bob. And, although my concept of time travel may have these sorts of strange consequences, you are yet to have proven it illogical.
Quoting noAxioms
If Bob succeeds in time travelling, then F-Bob does not exist. F-Bob only exists if Bob fails to time travel
There is either a timeline without a time travel event or there is a timeline with a time travel event. Call the timeline without a (any) time travel event timeline A and call the timeline with a time travel event timeline B. If there is no time travel event then timeline A results. If there is a time travel event then timeline B results (and timeline A gets overwritten by timeline B). F-Bob only exists in timeline A and S-Bob (the time traveller) only exists in timeline B.
Quoting noAxioms
If there had been no time travel events then F-Bob wouldn't exist.
Anyhow, your example doesn't leave a copy behind. When Bob time travels to a later time, he departs from the earlier time; he doesn't stay behind. However, he will meet an older version of himself in the later time (assuming that he travels to a time within his lifetime).
I need to make a correction here. I said earlier that forward time travel would change the timeline from the arrival time onwards. I should have said that forward time travel would change the timeline (from timeline A to timeline B) from the departure time onwards.
Quoting noAxioms
That's right. If there is no time travel event then the machine doesn't disappear. The machine only disappears if there is a time travel event. I didn't say that there both is and isn't a time travel event, such that S-Bob and F-Bob both exist on the same timeline. What I said was:
Quoting Luke
Quoting noAxioms
I'm just trying to get a better understanding of the distinction between the meanings of "happen(s)" and "exist(s)" in relation to an event/process under eternalism. You spoke of the time before the Titanic event when "it has not yet sunk" and the time after the event when "it is at the bottom of the ocean" (i.e. when it has sunk). You also said that "Somewhere between those two events does the sinking 'happen'." You noted "It's not much different than presentism except there is no preferred moment that has to somehow glide across that event in order for the event to cycle through the different ontological states of 'happening' and then 'happened'."
It seems very much as though there was a time before the event when the sinking had not yet happened, and a time after the event when the sinking had happened, and then somewhere in between those two times when the sinking was happening.
What was wrong with my depiction that "while the event is happening, it is cycling through successive ontological states with each successive state being the "preferred" moment," where "the "preferred" moment is the state that is happening, as opposed to those that have happened or have not yet happened."
Does eternalism allow only for the different ontological states of 'not yet happened' and 'happened', but not for the ontological state of happening? Does eternalism have anything to say about the process that changes an event's ontological state from 'not yet happened' to 'happened', or about any ontological state(s) between those two?
Quoting noAxioms
It seemed to follow from your Titanic example, where you spoke of times when the event had not yet happened and when it had happened, and you also referred to the "ontological state" of 'happening'. You will need to clarify whether any such events can happen or do happen or are happening in an eternalist universe.
Quoting noAxioms
To be clear, I was using the word "exist" in the latter, "ontological sense" given here:
Quoting noAxioms
You should learn that there are two ways of interpreting my sentence. I wasn't saying eternalists hold that each event exists at all times. I was saying eternalists hold that there exist events at each (and every) time, i.e. that there also exist events that are not present.
Quoting noAxioms
Nothing is happening in an eternalist universe? The sinking of the Titanic happened but was never happening?
I never gave any indication that she's stuck on the tracks. She's at the crossing, having to wait for it, a wait she cannot afford.
It's her first time. There's no loop of which she can be aware, except she knows that any use of travel to the past makes the past happen again, a loops of sorts. Look at Bob who goes and makes 1990 happen a 2nd time, but differently. That's a loop of sorts, but one that only 'happens' twice since his actions there prevent young-Bob from doing his 2024 thing.
None, which is why you model, if the machine doing a forward jump doesn't wait for the destination to be written, would match any of the typical fictions.
So either the machine must wait for the destination to be written, or if it doesn't, the machine appears in an unwritten future, which is blank.
All of them. It's not a wait from the traveler perspective of course. He arrives having aged but a moment with no memory of any waiting.
Sure you do. Jumping to Y3000 with a machine gets you to Y3000 just like Phillip Fry (who does it via Cryonics, an identical experience). Jumping to Y3000 via waiting gets you very very dead.
2035 is withing his own lifetime, so F-Bob (who I'm designating as the clone) is not yet dead, but he's 50. S-Bob (the time-traveling original) is 39 and meets his clone fact to face.
As I said, the machine has always been a cloning device. Bob goes back to 1990 where he meets another Bob. Two Bobs means one is a clone. Using this technique, you can make as many Bobs as you want, and you can do it quickly, in minutes instead of decades. So getting a clone by going forward is admittedly consistent with your going-back description, even if none of the fictions seem to depict that consistency. Hollywood has developed a rule that you can meet yourself if you go backwards, but not if you go forwards. There's no reason time travel has to conform to what Hollywood finds desirable.
Never claimed it was. Just an unusual choice of rules, since Hollywood does have an influence on most people's vision of what time travel would be like.
That's not what you said. You said the line is written as if the travel had not taken place (so it has F-Bob in it), but with S-Bob appearing in 2035, the destination event, which thus has both of them in it.
No, you said the line is written as if the travel had failed, so F-Bob very much exists in the line to which S-Bob travels.
You can of course abandon that assertion and say the line proceed as if the travel succeeded. Then the experience of Roberta is to see the machine disappear, and she's without her dad for 11 years. That's the typical hollywood depiction, but then the cloning property only works in reverse travel, not forward travel. You can still build the unlimited army, but the algorithm is slightly different.
OK, so A exists, the machine waits 11 years for line A to get to 2035, and then when it does, the history (with F-Bob) gets truncated back to 2024 and the machine has to wait an additional 11 years for the B line (no Bob at all) to get to 2035? Why can't the B line just be written from the start since F-Bob and the rest of the A line is doomed before the first moment is written?
No, if there had been no travel event, then S-Bob (the traveling one) doesn't exist.
Yes, as described just above. The machine has to wait 22 years now for two different histories to play out over 11 years each. Weird, but not contradictory.
Fine. The Robert in line A sees the machine stay put (fail), and a dejected F-Bob gets out The Roberta in line B sees it disappear and eventually meets S-Bob 11 years later.
Well, there was a time travel event in line A, but the observers in it have no way to tell. They would have been able to tell in 2035, but their line ends there, so they have no experience that would constitute a falsification test.
Processes are comprised of multiple events, and just like Earth (with spatial extension) can be treated as a point in some calculations, so can a process (a concert say) be treated as a point event so long as our precision is low enough that it doesn't matter.
Events are members of spacetime, thus exist in spacetime, just like locations exist in a 2D plane and thus exist within it. Since time is one of the dimensions of spacetime, the word 'happens' is meaningful. The event happens at the location in spacetime of that event, which I realize is circular, but that's the nature of a tautology.
Yes. The event of the Titanic Sunday Apr 14 has the Titanic in a state of 'not yet sunk'. It means that the sinking event (Monday, around 2AM) is a subsequent event in the ordering of all the events along the Titanic worldline. One can say that event A is prior to B, or A is in the past of B. Such relations are valid, It is the implicit reference to a preferred moment that is meaningless.
The statement about the Sunday event being a state of 'not yet sunk' simply says that the sinking event lies in the future of that Sunday.
There are a couple (bold) implicit references to the present in all that. To reword:
There is a time before the [sinking] event when the sinking had not yet happened, and a time after the [sinking] event when the sinking had happened, and somewhere in between those two times when the sinking happens.
The bit in brackets is not a correction, but just there for clarity so we know which event is being referenced.
Eternalism is unintuitive because A-series statements are just part of everyday language and is very hard-coded into our instincts. People mistake language for truth instead of the pragmatic utility that it and the instincts are. It is hard to remove an assumption that is so integral with one's everyday life. The assumption is put there very long ago by evolution because anything making such an assumption is more fit than something that doesn't. So to embrace eternalism, one has to set aside that intuition that protests at every step.
Several people were working on relativity theory, some getting a good head start on Einstein. But Einstein had the ability to ignore intuition when the intuition contradicted his findings. Others (notably Lorentz, Poincare) had a harder time with the implications of frame invariance and frame independent of light speed.
Besides the explicit reference to a preferred moment?
There are no such ontological differences. There is no division between such ontological differences.
[/quote]To be clear, I was using the word "exist" in the latter, "ontological sense" given here:[/quote]There are a lot of ways to use that word, and interpreting it one way doesn't mean that all references to the word mean that interpretations.
Wow, what a mix of multiple meanings and preferred moment references in a paragraph trying to clarify a view that denies the referent. I can see how the view might be difficult to learn from that source. Apparently there are using 'is present' to mean 'currently exists', which suggests that eternalism asserts that Socrates exists in 2024, which, itself can be interpreted as either 'Some of the events of the worldline of Socrates have a time coordinate of 2024', or as "All events exist, and a reference time of 2024 doesn't change that'. Only the latter statement is true under eternalism, and the paragraph above seems not to clarify which meaning is meant.
By 'not present', I am guessing that you mean 'not at the present moment' (as opposed to 'absent', which of course is not an eternalist statement.
Also not sure about the first part, that there exist events at each (and every) time. For instance, do there exist events before the big bang? I think not. Do all events have a time coordinate? I can't think of a single coordinate system that assigns coordinate values to every event that is part of spacetime, so even that isn't true.
BTW, by 'exists', I usually mean 'is a member of' relation. So an event existing means it is a part of the implied spacetime, the thing of which it is a member.
The statements as worded are both meaningless under eternalism, so instead of being true or false, both are more 'not even wrong'.
Your examples of the scenario were:
Quoting noAxioms
Quoting noAxioms
The problem is that you provided very little detail so it is difficult to follow what is happening in this scenario. Presumably, the DeLorean is a time machine, like in Back to the Future. So, Alice gets to the train tracks and has to stop because the gate comes down. She decides to use her DeLorean time machine to go back 30 seconds so that she can floor it and cross the tracks before the gate comes down (the second time around). All well and good. What I don't understand is, after she does this, why is there another DeLorean behind her getting stuck at the gates? The time travel event in your scenario does not overwrite the timeline.
Quoting noAxioms
I asked you which works of fictions involve time travel to a blank universe which has not been "written" yet. You tell me that there are no such works of fiction. Okay then, which works of fiction wait for the future destination to be written before time travel to that future destination occurs? By "wait", I assume you mean in the usual fashion, like you might wait for a bus? So you are saying that, in all works of fiction, there is no time travel to a future time which occurs before people have waited for that future time to happen? In that case, I don't understand why the time machine is needed.
Quoting noAxioms
Cryonics is not a time machine; not the sort we have been discussing, so not relevant to the discussion.
Quoting noAxioms
I made a mistake in my last post. Sorry, I've had COVID recently and wasn't thinking straight. I started out writing the post thinking that you don't meet yourself going forwards, but then I somehow reasoned myself out of it. So I agree with the Hollywood version; you don't meet yourself or clone yourself going forwards. You depart from an earlier time to a later time, so there's no other version of you left behind who continues aging normally once you depart from the earlier time for the later time. You can only "clone" yourself (in a sense) going backwards.
Quoting noAxioms
I never said that. Once again, what I said was:
Quoting Luke
The timeline that would have existed if there were no time travel events gets overwritten by a timeline with a time travel event. It gets overwritten in the same sense as backwards time travel: it inserts a time traveller into the timeline that originally had no time travel events. And, as per my correction, since Bob departs an earlier time for a later time, then there isn't a copy of him left behind who ages normally.
Quoting noAxioms
It is. I've said that what would have existed gets overwritten. We can imagine how the timeline would have existed if there had never been any forwards time travel, just as we witnessed how the timeline did exist without any backwards time travel just prior to the backwards time travel event.
Quoting noAxioms
Right, thanks for the correction.
Quoting noAxioms
It doesn't have to wait. It just travels there and overwrites what would have been.
Quoting noAxioms
Why do the observers need to prove it?
Quoting noAxioms
I don't know why you keep wanting to treat processes like points/events. I don't see the relevance.
Quoting noAxioms
It follows from this that "happens" is no different to "exists". It happens when it exists and exists when it happens - there is no distinction.
Quoting noAxioms
I defined the preferred moment as "the state that is happening, as opposed to those that have happened or have not yet happened". What's wrong with that? Does eternalism allow for events to have happened, and for events to have not yet happened, but not for events to happen? Why?
Quoting noAxioms
You described them as such in your Titanic example. You described a time when the Titanic had not yet sunk, and a later time when it had sunk, and then you said "Somewhere between those two events does the sinking 'happen'." This implies that there is a time when the sinking has not yet happened, and a later time when the sinking has happened, and a time between these when the sinking happens.
Quoting noAxioms
I didn't find it difficult.
Quoting noAxioms
The article distinguishes between "x exists now" in the temporal location sense and in the ontological sense. The distinction is clearly made.
Quoting noAxioms
Is "before the big bang" part of spacetime? The statement "there exist events at each (and every) time" does not require every event to be accounted for, as long as there exists at least one event at each and every time.
Quoting noAxioms.
It is only meaningful under eternalism to say that the Titanic has not yet sunk or that it has sunk and that "Somewhere between those two events does the sinking 'happen'? It seems like the past or future tense of 'happen' is acceptable, but that nothing happens (except sinking?) in an eternalist universe.
Does physics describe what the above even means?
:lol:
No, it doesn't. It is kind of like asking what physics has to say about if the sun suddenly wasn't there. Would Earth continue to orbit for 8 minutes or would it immediately commence a straight trajectory?
Another question: Does an infinite sheet of material (a meter-thick slab of concrete say) result in a uniform gravitational field?
Physics has nothing to say about either case since there is no way to describe what any of the above even means.
Luke is exploring a philosophical question about the implications of various philosophical models on the concept of time travel. The current model seems to be a sort of growing block model, which is full of contradictions, most of which have been left unexplored due to the slow pace of working through even the trivial bits.
Quoting Luke
Good. This is more in line with the typical pop vision of the time-traveling vehicle. Given our growing block model, the machine still has to wait for 2035 to come around before it can materialize in it. There's problems with that, but not obvious when there's but a single time travel event in consideration.
Also good that you recognize that any backward time travel machine is a cloning device. The traveler is the clone. The think I descried with the army-creator makes thousands of clone soldiers, plus a group of originals that have never time traveled. Keep all that in mind when considering the Alice example. The Alice that appears at the tracks and makes it across is the clone. The original Alice is the one that doesn't make it to the crossing on time. We can number the clones if there's more than one.
That's Alice0, yes. She's the original. She's never time traveled, not backwards at least.
By 'second time around' you mean the 2nd writing of those 30 seconds, yes. Alice1 makes it across the tracks. Alice0 is a half km back from the crossing and will get there in 30 seconds, 5 seconds after the gate goes down.
You seem only capable of imagining the traveler, just like Hollywood only follow the protagonist. Think about the others in the world at noon. Remember that Alice0 is in that world, half a km up the road, who is fretting about how tight her time is to make her appointment. She thinks about little else at the moment. Alice1 makes it across but Alice0 is about to erase Alice1's victory by hitting the button for the very first time in her life, truncating the history where Alice1 made it across. It sort of turns into a Groundhog-Day situation, except in Groundhog Day, the protagonist has memory of all the times through the loop. Alice doesn't. Alice0 has no memory of ever having time traveled.
It doesn't? You say it does. You said Bob going back to 1990 truncates history back to 1990 so it can be overwritten with older-Bob in it now, which is exactly what Alice0 is doing, except this time younger Alice0 is working the controls, not older Alice1. Are we changing the story again?
None that I know of anyway. Langoliers comes closest. The travelers arrive at a sort of blank future, but stay put at the moment of arrival until the 'present' catches up with them and suddenly everybody appears. It's one of the few stories that really leans on presentism, where the author is very aware of his model and tries to be consistent with it.
No, waiting for a bus takes subjective time, experienced by the waiter. The experience of the traveler is no waiting. The world is simply there when they arrive, sort of like super-fast spaceship and time dilation. I can go forward 11 years in a moment without having to experince waiting, if my ship is fast enough. And SEP apparently designates that as actual time travel, despite my protests.
I don't think many works of fiction explicitly rely on this growing-block model that you have going on here, so concepts like a new history growing simply don't apply. But also, many (most?) time travel stories never depict the viewpoint of somebody other than the traveler. Dr Who has gotten a lot better about that since it was resurrected. The writing has gotten better and many stories are told from different viewpoints, including episodes mostly without the doctor or machine in it at all.
The machine has to wait. The people never do, since the experience is instantaneous to them.
I didn't say Cryonics was time travel. I said the experience is essentially the same to the traveler: (Step in, step out into some future year). The experience of the outside observer is not the same because they can see the machine with Cryonics, and it 'disappears' presumably if it's a time machine. Both machines have to wait for 2035 to happen, but the time machine apparently waits in some inaccessible dimension or some such. No explanation is yet given as to where it is en route.
OK, this is new. It just makes up a plausible state for 2035? None of the intervening years actually happen, the state is just put there? How very last-Tuesdayism. BTW, I am a total fan of last-Tuesdayism, not that I assert it, but it is something everybody needs to attempt (and fail) to falsify.
I'm fine with that. It's consistent with the God-like powers the machine needs anyway to go backwards, so if it can set the present to 1990, why not make up a 2035? You don't even need growing block then. It can just be raw presentism, where the 1990 it creates isn't actually what the real 1990 looked like back then, but it's consistent with what is known about 1990 in 2024.
This is also very consistent with the 2nd Back to the Future movie, going to a totally made-up 2015 that looks nothing like what the actual 2015 would have looked like had the machine waited for the real timeline to grow to that point.
I gave examples of the difference between the words, where substituting one for the other in a sentence would result in a wrong statement. So no, they're not synonymous.
I never said either. It happens at the time of the event. It exists in spacetime. All events exists in spacetime, but they don't all happen at any given time since the time of one event may be different than the time of another.
Yes, that's how a presentist might define the preferred moment. But that moment is not postulated in eternalism. If you want to understand eternalism, don't drag in definitions and premises from an incompatible view.
Meaningless due to the implicit references to the present. One can say that relative to 2080, 2070 has already happened. That's an explicit relation reference. Tensed verb work as long as the reference moment is explicitly stated.
Both are meaningless. They are both references to the present. How can you not see this?
Yes, all references to explicit times, not implicit references to the present.
Not our spacetime. The geometry outside our spacetime is not really known, It isn't know if 'geometry' is the right word for it even.[/quote]
First of all, the statement is false since I can think of a time that has no events. Secondly, I know of no coordinate system that accounts for every event (assigns a value to its coordinates), so the bit about a requirement of all events being accounted for is not there for a coordinate system, but it kind of is there for spacetime. Spacetime is physical. Coordinate systems are abstractions.
Not even wrong.
The phrase "nothing is happening" is not a meaningful one in an eternalist universe, so the truth of the phrase cannot be assessed.
If Alice0 is the original, then how is she able to see Alice1 driving off on the other side of the tracks as you claim? I thought that the car on the other side of the tracks was the original Alice after she had time travelled. Since she hasn't yet time travelled, then she cannot possibly see a copy of herself driving off on the other side of the tracks. The car on the other side of the tracks must be the original Alice for the scenario to make any sense.
Quoting noAxioms
What is Alice1's origin story? How do two Alices exist before any time travel occurs?
Quoting noAxioms
I think I'm quite capable of imagining both perspectives.
Quoting noAxioms
If Alice0 has never time travelled, then where did Alice1 come from? As I said,
Quoting noAxioms
The time travel in my model does overwrite the timeline, yes. I was referring to your Alice and the train tracks scenario, which does not. Hence, your scenario is an ineffective argument against my model.
Quoting noAxioms
Your argument is supposedly that my presentist model entails a blank future universe. However, as I said, I am neither a presentist nor an eternalist, but a mixture of both. I could say that the future has a definite physical existence prior to the time travel, but it gets overwritten by the forward time travel event anyway.
Quoting noAxioms
You can also go forward a few hours without having to experience waiting simply by sleeping (or by being in a coma). However, the SEP article designates sleep, coma, cryogenics and waiting as not actual time travel.
Quoting noAxioms
Really? I think many works of fiction depict time travel as I depict it in my model, where the time traveller travels to, and inserts themselves into, a time they have never visited before (as a time traveller). For example, Marty McFly was never in 1955 prior to his first time travel event, and his time travel results in changes to the 1985 he departed (i.e. he overwrites the timeline).
Quoting noAxioms
Presumably backwards time travel works differently. Why should the machine have to wait in forwards time travel if it is not required to wait in backwards time travel? I imagine that the time machine can immediately transport the passenger from one time to another.
Quoting noAxioms
Why do the events happen in a sequence when they don't exist in a sequence? That is, events do not flow into and out of existence sequentially in an eternalist universe, like they do in a presentist universe. So, why do they happen sequentially in an eternalist universe?
Quoting noAxioms
Right, tables don't happen but events do. I should have qualified this to say "happens" is no different to "exists" in relation to events. But I thought this was already implied by the context.
Quoting noAxioms
This isn't making any distinction between "exists" and "happens". You could exchange these words in your above statement without changing the statement's meaning.
Quoting noAxioms
I didn't drag them in; you did with your Titanic example. The time at which an event happens, or is happening, is the preferred moment ("preferred" in the sense that it has not already happened and is not yet to happen but is, as you say, "somewhere in between").
In your Titanic example, you referred to a time when the event had not yet happened and to a time when the event had happened, but you also want to distance yourself from saying that the event is ever happening. This is illogical. If it is going to happen (relative to some time earlier than the event) or if it did happen (relative to some time later than the event), then there must also be a time when the event is happening (relative to some time simultaneous with the event).
You noted that your Titanic description of what it means for events to "happen" in an eternalist universe is "not much different than presentism". I agree. I think "happens" is a presentist term (i.e. which only makes sense in a presentist universe) which makes little sense in an eternalist universe. It is my view that nothing ever happens in an eternalist universe. If nothing is ever happening, then nothing will ever happen or did ever happen. The word loses its meaning, except as a synonym for "exist".
You clearly reject any sense of the word "happen" which is associated with a "preferred moment", yet you say your Titanic description involving the word "happen" is exactly like presentism, only without the preferred moment. I don't think anything remains of presentism if you subtract the preferred moment. Therefore, if "happen" has the same meaning in eternalism as it does in presentism only without the preferred moment, then I think the word "happen" (in relation to events) under eternalism loses its conventional meaning and can only be used synonymously with "exist".
Quoting noAxioms
Right, "happen" should not refer to any transpiration or progression of events in eternalism. I agree. For the sake of consistency, it should be used to mean nothing other than "exist".
Quoting noAxioms
You referred to these different "ontological states" in your Titanic example. Here it is again:
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I thought your example was intended to clarify the meaning of "happen" in eternalist terms.
Quoting noAxioms
The reason I asked was because you said:
Quoting noAxioms
You seemed to be arguing that there are no events before the big bang even though there are times before the big bang, therefore falsifying my statement that "there exist events at each (and every) time. Do you believe that there is time (or that there are times) before the big bang? If not, then I don't follow your argument.
Quoting noAxioms
Under eternalism?
Quoting noAxioms
I said that it is not required that every event is accounted for, so I don't have any "bit about a requirement for all events being accounted for".
Quoting noAxioms
Right, even the use of the word "happening" isn't meaningful. That's because nothing happens (in the conventional sense) in an eternalist universe.
Well, I think any reasonable philosophy needs to take into account the facts as we best understand them. According to General Relativity time is the fourth dimension of spacetime. Talking about "overwriting" the "timeline" is like talking about "overwriting" the "heightline" or the "widthline" or the "lengthline". It seems pretty nonsense.
What does it mean to "overwrite" a direction in space(time)?
I'm reasonably sure General Relativity is a theory, not a fact.
Quoting Michael
It might seem nonsense if you adopt an eternalist view of time, but that's not a fact either.
We were discussing time travel. The question posed by the OP is: is time travel to the past hypothetically possible? I'm sure you've heard of time travel before, where a time machine is used to transport the user to a different time. I never suggested that time travel was genuinely physically possible according to our known physics and/or technology, but if it were at all hypothetically possible, then the time traveller would supposedly travel to a time that they had never visited before (at least, in their role and at their age as a time traveller). If we assume backwards time travel, where the arrival time is earlier than the departure time, then, prior to the time traveller's arrival at their destination time, there exists a history which is has not yet been visited by the time traveller. Once the time traveller arrives at their destination, then that unvisited history changes, or is overwritten, by the time traveller's inclusion in that history. That's what it means to overwrite a timeline, or history, or an earlier time, as supposed in many fictional time travel scenarios.
I've never made any claims about overwriting a direction in space(time). That would assume an eternalist view of time, in which time is treated much like a length, or as another spatial dimension. Whereas - prior to the untimely demise of this discussion - I was seeking to explore the limitations of eternalism, such as its logical omission of progress, happening or motion; characteristics that I consider to be absent from eternalism but logically aligned with the opposing view of presentism. However, many eternalists disagree.
I find it worthy of an interesting philosophical discussion, but I suppose you've made up your mind already. What I don't understand is why you felt compelled to interrupt a discussion that's been developing for over five pages only to denounce it as "pretty nonsense". You could always just mind your own business.
:up: :up:
https://thephilosophyforum.com/discussion/comment/690858 :nerd:
I assume you're also against the growing block theory of time?
If you're arguing for presentism then this might be interesting:
Presentists Should Not Believe in Time Travel
The general gist being that the very concept of traveling to the past depends on the past existing in some sense as a location to travel to, and so requires either the growing block universe or eternalism.
If presentism is correct then any supposed time machine would work by rebuilding the universe into a facsimile of one of its past states, which isn't really time travel.
Quoting Luke
If there exists a history then presentism is false.
I'm not against the growing block theory, per se, but I don't necessarily consider it to be the view that I hold.
As I explained previously in the discussion:
Quoting Luke
Quoting Luke
So, I don't consider myself to be a presentist, either, but I do think that presentism should not be entirely rejected. Its progression - the natural progression of a present moment - is very important to our concept of time, and this belongs entirely to presentism imo. Even if the concept of an objective present moment is rejected, I don't believe that progression - the march of time - associated with it should be also. This temporal progression is too easily assumed as equally belonging to eternalism or as logically coherent with eternalism, but I don't believe it is. This progression is also a very difficult concept to quantify or to describe in language. I believe this is partly why it is so commonly rejected by eternalists.
I have presented my views on time previously on the forum, e.g. in this discussion. The argument I present below can also be found in the same discussion at this post, although I have tried to strengthen it a little more here.
Argument against motion in eternalism
A major difference between presentism and eternalism is their differing concepts of an object. Presentism takes the commonly held view that an object is 3D and traverses time. Eternalism takes the uncommonly held view that an object is 4D, that the 4D object exists across time, and that it consists of 3D parts.
If we consider that the motion of an object is basically a change in its position over time, then it can be shown that this can only apply to (the presentist view of) a 3D object. This is because, according to presentism, the same 3D object exists at different times. However, according to eternalism, the same 3D part (of a 4D object) does not exist at different times.
If I travel from London to Paris, then I am considered as a 3D object that departs from London and arrives in Paris. Before I have departed from London, I do not yet exist in Paris and after I arrive in Paris, then I no longer exist in London. However, this is not the case in eternalism, where I exist as a 4D object, not as a 3D object. In eternalism, I exist across time with a part of me existing in London at one time and another part of me existing in Paris at another time. But the 3D part of me that exists in London is not the same as the 3D part of me that exists in Paris. No part of me departed from London because that (London) part always exists there, and no part of me arrived in Paris because that (Paris) part of me always exists there. And all the parts of me in between London and Paris always exist there. In a 4D object, there is no change in position or time of a 3D part, because all the 3D parts are different.
It is only in presentism, where the same 3D object can change its position over time, that an object can move.
Eternalists may treat a 3D part as though it were a 3D object, but in doing so they should recognise that they are adopting a presentist view.
Just spit balling but how about:
Physical objects are 4D objects extended in space and time as per eternalism.
Consciousness is a non-physical 0D "object" bound to some physical object.
Time doesn't flow but consciousness travels through (its physical host's) time.
The consciousness of what? If you mean the consciousness of the 4D host, then that is extended across time and doesn’t move. If you mean the consciousness of a 3D part of that 4D host, then all the 3D parts are different and none of them moves.
My random idea is that the physical host is something like a tunnel and consciousness the occupant. The tunnel is fixed in time and space with consciousness travelling through it.
I understand. However, I’m assuming that the consciousness has a physical basis on the host. I’ve given arguments for why neither the 4D host nor a 3D part of that 4D host moves. Therefore, I can’t see how the consciousness of either the 4D host or a 3D part could move.
I suppose you could posit some sort of disembodied consciousness, but I think any reasonable philosophy needs to take into account the facts as we best understand them.
So time flows for consciousness but not for the physical host. At the very least it could tentatively explain the current conflict between general relativity seeming to imply physical eternalism and our everyday experience seeming to imply presentism.
Of course this would seem to entail determinism, unless something like the many worlds hypothesis is true and consciousness can choose which “world branch” of the 4D host it travels down.
[quote=Hermann Weyl, Philosophy of Mathematics and Natural Science (1949)]The objective world simply is, it does not happen. Only to the gaze of my consciousness, crawling upward along the life line of my body, does a section of this world come to life as a fleeting image in space which continuously changes in time.[/quote]
But if the host’s consciousness supervenes on the physical body of the host, then you need to counter my argument to explain how that consciousness can move, given that the physical host does not.
But again, I’m just spit balling.
I'm simply presenting an alternative view, I'm not trying to argue against your view.
Quoting Luke
Yes, and this is apparently in conflict with general relativity (and time reversibility?). So I'm offering a hypothetical solution that might resolve the conflict between this and our everyday experience of the (one-way) passage of time.
Quoting Luke
I don't know. Much like I don't know how, according to physical presentism, physical objects can move through the unmoving space(time) that underpins them. Again, I'm spit balling. I don't have some consistent and complete mathematical model at hand.
Quoting Luke
Because, as above, it may resolve the conflict between general relativity and our everyday experience of the passage of time. If dualism is correct then the physical and the mental need not necessarily behave according to the same laws.
But I am arguing against your view. My argument against motion in an eternalist universe does not allow for the motion of consciousness over time if that consciousness has a physical basis; where the motion of that consciousness is dependent on the motion(s) of the physical host.
Quoting Michael
How is it in conflict?
Quoting Michael
Your solution seems to be simply that consciousness moves when nothing else does. This does not explain why we experience a one way passage of time, it only allows for us to do so; it presupposes the experience of time that we have.
Quoting Michael
It’s not really analogous. We can see the effects on consciousness from damage/changes to the brain, for example. There is no similar study we can do to see how damage/changes to “unmoving space(time)” affects physical objects.
Quoting Michael
That’s not something I believe, and I doubt it takes into account the facts as we best understand them.
Sorry, it was special relativity, not general relativity:
For example, see the conventionality of simultaneity.
Quoting Luke
Well, yes. I think it self-evident that I experience the passage of time. I want a theory of time that can account for that.
Quoting Luke
There's perhaps gravity and any curvature of space(time) in general.
Quoting Luke
It's something I believe. I'm unconvinced that physics alone can explain the hard problem of consciousness.
Quoting Luke
Again, I'm spit balling, not trying to argue for it. It was really just an off-hand remark, not something I intended to lead to a rigorous discussion.
Quoting Luke
An I don't understand why you let the interruption halt the discussion.
Quoting Michael
You're confusing the timeline with the time axis/dimension. The latter is nothing more than a sort of state of what happens in a particular world.
Quoting Michael
Quoting Luke
All of your responses (since branching had been abandoned) seem to describe pretty much a growing-block view, with travel to the past truncating the block and resetting the present to the new destination time. You shows little understanding of a view that isn't some kind of presentism (as evidenced below). I can't think of a label that better describes what you've been describing.
Quoting MichaelI was trying to work with it. It is actually 'travel' under presentism, as opposed to a sort of discontinuous (or at least not time-like) worldline you get under eternalism. But yes, traveling to a time that isn't the present creates all sorts of problems, solved by the apparent god-like ability of the machine to rewrite the present state of the entire universe.
Growing block is a form of presentism, and under that, there is at least a past to which one can travel, but getting that state to be the new 'present' is the big trick.
Moving spotlight is another form of presentism, but once again, requires a god-like power to control the spotlight, hard to do if everybody has such a device.
Growing block is a form of presentism, and has a history.
Quoting LukeYes, commonly held, but not by physicists that understand relativity theory.
The present is 3D. Growing block and moving spotlight are also presentism (positing a preferred moment that traverses time), but still have 4D spacetime.
3D parts of what?? Any object (a car part say) occupies a 4D volume of spacetime. I can't think of a 'part' that is 3D. One can take a 3D cross section (in any direction, not just space-like), resulting in a 3D subset. I think that's what you're referencing.
Yes, true under both views.
, then it can be shown that this can only apply to (the presentist view of) a 3D object. This is because, according to presentism, the same 3D object exists at different times. However, according to eternalism, the same 3D part (of a 4D object) does not exist at different times.
Quoting Michael
That sound a lot like moving spotlight, but in the absence of presentism (with a yet unwritten future), it boils down to epiphenomenalism, sort of like watching a movie where the experiencer is in no way capable of influencing the character being experienced.
Time travel is possible though this, but instead of old-Bob physically appearing in the past, the mind experiencing Bob just 'switches channels' and moves his personal spotlight to something (presumably a different person) at some other time.
Quoting Michael
Both imply (but don't explicitly require) a lack of an objective present. SR is nice, but is a local theory, only describing one's immediate environment and not the universe in which we actually live.
GR does not posit (or imply) a present, but there is a sort of preferred frame in which the mathematics is easier. It isn't an inertial frame. That part is kind of in conflict with the first SR postulate that the physics is the same in all frames. Well it isn't. It's more complicated in the other ones. Einstein was not pleased with this outcome.
The experience of time is the same under both views. Relativity theory is not in any way a theory about how biological experience works.
Quoting LukeSpacetime does not change. It isn't embedded in time, so it cannot evolve over time. Objects ARE contained by time, and thus change over time. Treating spacetime as an object is a category error.
You state a disbelief in spacetime and relativity theory. That's fine, but a lack of understanding doesn't put you in a position to criticize the consensus* view.
*among those with understanding.
All this aside, I'm trying to put together a comprehensive analysis (probably naive) of all the different interpretations of relevant ideas, so show how some views are blatantly in contradiction with time travel, and others might not be. The branching seems to avoid most of the contradictions, but as @Christoffer points out, it isn't really travel then, is it?
I would post the think in this topic, but it's so far down the rabbit hole and making no progress that I think it better to be it's own topic, one where I'm driving instead of just replying to ideas of others.
Yes, because most people are not physicists that understand relativity theory. Hence, "commonly held".
Quoting noAxioms
3D parts of the 4D object. I thought I made that clear. I said the 4D object consists of 3D parts.
Quoting noAxioms
Whether or not objects have extension through time is the subject of our temporal debate, not a given. Otherwise, you are begging the question.
If all objects are 4D objects and have temporal extension, then at any given time only a (3D, temporal) part of that 4D object exists, and the different parts of that object exist at different times. A presentist might say instead that the object does not have temporal extension and that the same 3D object exists at different times. For example, you are the same object/person you were as a child. Whereas an eternalist might say that you-as-an-adult and you-as-a-child are different (3D) parts of the same 4D object.
Quoting noAxioms
Yes, I'm referring to a whole 3D object at any given time (of its existence) or, alternatively, to a 3D part of a 4D object at any given time (of its existence).
Quoting noAxioms
No, it's not true under both views. Under presentism, the same 3D object exists at different times. Under eternalism, different 3D parts (of the same 4D object) exist at different times. That's why 3D parts cannot be said to move; it's not the same 3D part at two different times.
Quoting noAxioms
Right, that was my point. I don't understand why you are directing these comments at me instead of at @Michael.
Also, please learn how to quote text on this forum. The formatting of your posts makes them difficult to follow (and to reply to). After you highlight some text, a little box should pop up somewhere on the screen with the word "quote" in it. Just click on the little box.
For instance, you seem to be able to discuss black holes probably because you've heard the term on pop-science sites or the news or whatever, but only Einstein's theory predicts them. They cannot exist under presentism of any kind. So the commonly held view is also self-contradictory, which is simply not a concern of the average guy on the street. Probably 99.9% of everybody holds views somewhere that are mutually in contradiction. But most of those people don't argue on forums for the consistency of the specific points that are in contradiction with each other.
I see what you're saying. It's a funny way of putting it, but I suppose so. I would have called them cross sections instead of 'parts'.
All this is a side topic. We need to make progress since almost none is being made in a 200+ post topic.
None of the post was about time travel, and your rules continue to be evasive.
Suppose I take my (stationary) machine and go back half a second. There's obviously a machine sitting at the targeted destination, so where do we materialize? Does the machine of 1/2 second ago get trod upon and destroyed, both machines destroyed (car crash style), or does it find somewhere/somewhen else to materialize? What's the rule here?
I really couldn't make progress on the Alice example without knowing how you envision this.
You've made this unsupported accusation several times. What makes you think I'm ignorant of the theory of eternalism?
Quoting noAxioms
For someone who regularly accuses me of ignorance of concepts in the philosophy of time, I find it amusing that you are obviously unfamiliar with the concept of temporal parts.
Quoting noAxioms
Before your break, we were discussing whether events can happen (or be happening) in eternalism, so I don't consider a further discussion of the implications of eternalism to be a side topic. You appeared to be arguing that eternalism is the only theory that can make sense of time travel. Besides, you completely ignored my argument against motion in an eternalist universe, just as prior to your break, you never replied to my argument that Alice0 cannot be the original Alice.
Quoting noAxioms
I'm not being "evasive". I've already answered this:
Quoting Luke
You do seem to be more familiar with the glossary as used in the philosophy sites. I come from more of a physics background where such terms and distinctions are not important. I've never heard a physicist refer to a 3D part of a 4D object, but apparently SEP is full of that sort of thing, and you linking to those sites has helped me see what the language is all about.
It seems I am.
The SEP site describes spatial parts that are extended (hand, feet and such), but when it comes to temporal parts, it seems not to allow any extension to them, which seems an inconsistent use of the term 'parts' to me.
The article is supposed to be describing a form of eternalism, but it still makes plenty of references to 'the present, past, and future', which begs a different view.
Physics doesn't seem to care about the distinction between perdurantism and endurantism, and the difference seems merely one of language. The views don't seem actually different in any physical way, so I couldn't really say which of the two I'd side with if I had to choose one.
It seems one finds meaning to the question of 'does a 1947 event exist in 2047?', and the other view does not find the question meaningful as worded.
This is also mostly a choice of how to use the language, but the tense 'can be happening' in the absence of an explicit time, constitutes an implicit reference to the present, and such references should be avoided. I've said this repeatedly.
Not at all, but it treats it differently. Different interpretations work in one interpretation or the other, but most not in both.
Motion in a block universe is a difference of location over time, just as it is in presentism. What was you argument against that again? Do you deny this definition, or deny that it applies to either view?
As for which Alice is the original, I simply chose a convention. I never argued that a different convention was necessarily wrong. The Alice story can be told using either convention.
Also, it was you that took the break, never replying to anything from my post a week ago.
Then time travel is mostly impossible the way you envision it since there is always something (air, dust, bugs, trees, whatever) at the destination, unless one chooses to materialize in deep space, and none of your scenarios do that. But here you suddenly suggest that materialization at a location that already has something results in the destruction of the machine and whatever was there before.
If it materialized in deep space, the machine would be wonderfully useful for budget space travel. Other worlds could be populated effortlessly, a task currently not feasible.
So Alice goes back 30 seconds, crosses the track, and the Alice behind travels back 30 seconds later and lands on the first traveling Alice, and both traveling Alices die, leaving just the younger Alice approaching the tracks, who finds the wreckage of the collision there, and thinks twice about adding herself to the heap. Problem solved, but Alice misses her interview appointment and doesn't land the desperately needed job,.
Are you referring to my attempts at such descriptions? Or your attempts? Or just attempts in general?
If you mean the former, then no, I do not see eternalism as containing any flow or motion. It is your assumption that events happen (which you differentiate from mere existence) in an eternalist universe which suggests some sort of flow or motion in an eternalist universe. Otherwise, you still have not made clear how the existence of an event differs from the fact that it happens. I don't believe there is any difference under eternalism, but you claim there is.
Quoting noAxioms
Glad I could help. This is The Philosophy Forum, not The Physics Forum.
Quoting noAxioms
The article describes the two main views of temporal parts (or persistence): perdurantism and endurantism. Perdurantism is more aligned with eternalism and endurantism is more aligned with presentism. The way I remember it is they have the opposite starting letter; eternalism = perdurantism, presentism = endurantism. Perdurantism has temporal extension; endurantism does not.
Quoting SEP Temporal Parts
Quoting noAxioms
Motion and/or location of what, though? Objects. Eternalism has 4D objects (with 3D parts). Presentism has 3D objects.
Quoting noAxioms
My argument is that the definition of motion as 'a difference of location over time' is something that can only apply to 3D objects. This is due to my argument against motion in an eternalist universe or argument against motion of 3D parts (of a 4D object).
My argument against 3D parts (of a 4D object) moving or changing location over time is that all the 3D parts of a 4D object are different and exist at different times. Since each 3D part (of the 4D object) exists at a different time, then no 3D part moves or changes its location over time. It would be analogous to part of a steel bar "moving" along its own length; it doesn't happen.
Quoting noAxioms
I don't deny the definition. It applies to both views, but there is no change of location of any 3D part in eternalism.
Quoting noAxioms
What are you talking about? Before you took a break, I posted this reply to you. You never responded and were absent from the discussion for a week afterwards. Then, two days ago, you posted:
Quoting noAxioms
I have no idea why you think I never replied to your post from a week ago.
Quoting noAxioms
How would air, dust or bugs at the destination prevent time travel? If the machine can time travel, then it can probably find a safe place to arrive.
Quoting noAxioms
The quote was from over a week ago. I didn't "suddenly suggest" it.
Quoting noAxioms
You've lost me here. There are three Alices?
Alice goes back 30 seconds. Okay. Then there is also an "Alice behind". Is she the same Alice as the one who just went back 30 seconds? Apparently not, since those two Alices die after one lands on the other. So, where did "Alice behind" come from? However, now a third Alice approaches the tracks to find the wreck of the collision that killed the other two Alices. Where did third Alice come from? Was it only the first Alice who time travelled? If these are different people then why did you call them all Alice? This is very confusing.
Water flows. The wheels on the bus move. The sinking of the Titanic happens in 1912. None of those statements imply a presumption of a preferred moment in time, and that one presumption is the only fundamental difference between the views.
I didn't read it that way. The endurantists statements you make seem to consider objects to have temporal extension (since a reference to 'wholly present is a reference to all events in the object's worldline, and that is, in the absence of a preferred moment presumption, an eternalist stance.
The endurantist stance, as stated, needs clarification since it seems contradictory. First of all, there is the statement about being present (not absent) when it exists, but 'when it exists' is ambiguous. Consider the Andromeda 'paradox'. Is the en-route invasion of Earth fleet wholly present in 2024 or does it absent, according to endurantists? The answer is ambiguous due to relativity of simultaneity. The presentists don't have this problem with the Andromeda scenario.
The other contradiction I see:is that I wholly am present in the year 2000, which includes my tonsils, but my tonsils in particular are absent in 2000, so they are both present (as part of something present) and absent in 2000 (as just the tonsils), a contradiction. So as I said, clarification is needed to clean up such examples.
The science community cares not at all about such distinctions, and the time travel question becomes a scientific one once we have empirical descriptions of how it all works.
Objects of course. I'm at home at noon, and at grandma's house at 1, a different location (relative to the frame of the surface of Earth) over an hour's time.
If you get anal and take my attempt at the the endurantists wording of the situation, then "Relative to the coordinate system of the surface of Earth in timezone X, the events in my worldline that have the temporal coordinate 'noon' have the same spatial coordinates as 'home', and the events in my worldline that have the temporal coordinate 'at 1' have the same spatial coordinates as 'grandma's house'.
But that's a mouthful much more easily expressed with "Between noon and 1, I move from home to grandma's house".
Well I just applied that definition to a 4D object just above.
OK, this is just a refusal to use the typical identity convention, that me at one moment is not the same me a second later, but rather two separate entities. Regardless of a presentist or eternalist stance, if that identity convention is used, then indeed, nothing can move, by definition. There are valid attacks on the usual identity convention, so this can be a reasonable alternate convention. I think I can disassemble any identify convention by choosing the right example, so I don't suggest any one convention is necessarily correct.
It sort of has all sorts of moral implications, that one cannot be held responsible for something a different entity did yesterday. It's an interesting exercise to argue why that statement is not so much true, but rather meaningless given the assumptions made.
Another counterargument to the whole 'separate 3D parts' interpretation is that a 3D part is coordinate system dependent. There are different was to slice a 4D worldline into 3D cross sections, and absent a preferred angle of slicing, there are not actually any 3D parts, but rather only utterly separate 0D events that are the 'parts'. The perdurantist stance doesn't seem to get into this, perhaps because the adherents are not really up on the physics from which all these eternalist views sprung in the first place.
The SEP article on temporal parts seems to mention some of these problems in section 7, but without resolving any of them.
That usage of 'move' does not conform to the definition given, so no, it isn't analogous.
My bad. Some of the notifications are not coming through. Will try to reply to parts not covered since.
I asked for how you envision interaction with material already present at the target destination. Your answer was simply 'die/explode'. So perhaps the answer needs to be changed. Maybe it handles air better, by what, pushing it aside first? Absorbing it (which probably covers 'die' pretty well)? The answer you gave does not imply that it simply replaces what was there with a new state (terminator style, except with electrical effects preceding).
So if explode/die is the wrong answer, then what is the actual answer? If air is treated differently than other material, where is the line drawn, and how about the bugs, which are definitely not air? How about the tree I mentioned?
That's a different answer. So it assesses the target, and selects somewhere close? Does it have a limit as to how far (both spatially and temporally) it is willing to look for a satisfactory point in which to insert itself? What does it do with the stuff that is already at the selected point?
Alice hits the button to go back 30 seconds and finds herself on the tracks with the gates already down (just like in BTTF) and with a train 3 meters away. Hey, it was the nearest available spot...
I need to know the rules so I can illustrate the contradictions that result from those rules. We've not even attempted everybody having such a machine yet. I can't imagine how many questions it's going to take to get a clear model of that, but it probably won't happen because the machine you envision erases history, so in very short order, all those other machines will be erased from history by the person who travels backwards the furthest.
Two travel events (both by younger Alice, traveling for the first time ever), each one making a clone, so yes, three of them. Did you forget the machine makes clones?
Depends on your identity convention. Which do you consider to be the original in the just-truncated history, the one that traveled, or the younger one that has not, but is about to? When she does, at noon there are two or three Alices, depending on the microsecond timing. If the 2nd destination event happens ever so slightly sooner than noon, it erases the noon event of the appearance of the Alice that makes it across the tracks, and there still remain two Alices, the one that just appears, and the one 30 seconds back that is approaching the crossing and is going to hit the button in 30 seconds.
If the timing is the other way (which it must be eventually), the 2nd travel event lands exactly on the first one, and the whole explode/die thing occurs, leaving only the younger Alice who will get to the explosion scene 25 seconds after noon.
She is always there. Nobody traveled back far enough to erase her from history. She's the one that has never traveled before, and is late for her appointment.
It seems you convention is to consider the traveler to the original, and the other in the timeline to be the clones.
So in the Bob thing, the original Bob goes back and kills his younger clone, who is not Bob, but rather clone-Bob.
I had been using a different convention, but which one used doesn't matter except when we assign names.
Using your convention, the original goes back (Alice1), who crosses the tracks,. Alice2 is 30 a clone, 30 seconds younger, and will get to the track in 25 seconds and will decide to go back 30 seconds to make it across. Alice2 goes back to noon, explodes and dies in a collision with identically aged Alice1 who also appears just there, and Alice3 (30 seconds younger than 1 and 2) will get there in 25 seconds.
They are all Alice, but I put numbers on them to keep track of the clones. I used your convention.
From last week:
Much of the confusion early in that post is my using a different identity convention, where I consider, in a timeline resulting from a travel destination event, that the traveler is the original and those pre-existing in the timeline are the orginals. The story as reworded above utilizes the opposite convention where the traveler is designated as the original.
If it doesn't wait for the destination to be written, then yes, it is blank. If it just makes up a state to write into that blank space, then fine, it puts something there, all very BTTF. Nobody can tell anything is weird except those who witness (or better, catch on video) the appearance of the time machine out of nowhere.
Your model had truncation. This statement seems in contradiction with that term, which sort of implies that when the present is moved back to 1990, the written state of things between 1990 and 2024 is reverted back to a blank state. Now you suggest otherwise. All very self contradictory. Perhaps more clarification is needed as to what exactly happens to the 34 years between when the present is moved back to 1990.
You say you're not necessarily a presentist, but you've been describing something that matches only growing-block theory, and matches nothing else. This more recent statement is more like moving-spotlight, where 'the future' is sort of written (exists), but is not yet at the preferred moment.
And encounters a slow version of the grandfather paradox where he is threatened with nonexistence by changing the circumstances leading to his birth, a different story than the one you tell. Anyway, that story is full of contradictions, and it doesn't explicitly call out the interpretation of time it is using. The movie probably contradicts any valid interpretation of time.
In a growing block model, the past exists but the future does not, but will eventually. Hence the wait. In a moving spotlight model, both exist, and it is merely a matter of 1, moving the spotlight, and 2, creating a destination state that is compatible with the identity convention of choice. In raw presentism, backwards time travel is impossible because the destination doesn't exist, and never will again. Under eternalism, a branching model in Hilbert space is probably the best, but world creation is not really time travel without a simultaneity convention between separate worlds.
Putting them in a sequence is a choice, a natural choice, as I've illustrated. I can create a series of pictures that a child can order in apparent causal order, not necessarily in the order in which the pictures were drawn.
I don't argue for meaningful time 'before the big bang', given a realist definition of the universe as 'all there is', there would probably be more than what is accounted for by just the spacetime that we know. The ability to temporally order the other parts is likely meaningless, so different language is needed to discuss such things.
The observation that "those words can be applied to a block view" doesn't make it logically consistent (with eternalism) to do so. We can observe many uses of words that are nonsensical or logically inconsistent with one theory or another. I don't believe that it is logically consistent, within the theory of eternalism, to apply terms like "happen", "move" or "flow" to objects or events in a block universe.
Quoting noAxioms
They all imply motion which, I believe, is the more fundamental difference between the two views.
Quoting noAxioms
Then I believe you've misunderstood the article. The introduction states (my emphasis):
Quoting SEP Temporal Parts
This is the perdurantist view. It is consistent with eternalism due to the temporal extension of its objects which are, therefore, divisible into temporal parts. The introduction continues (my emphasis):
Quoting SEP Temporal Parts
This is the endurantist view. It is consistent with presentism due to the lack of temporal extension of its objects which are, therefore, not divisible into temporal parts.
To repeat, from the article: "Endurantists believe that ordinary things do not have temporal parts; instead, things are wholly present whenever they exist (things persist by ‘enduring’)." Therefore, the phrase "wholly present" is not, as you say, "a reference to all events in the object's worldline". That is, unless it refers to a presentist object's worldline, which extends no further than the present moment.
Quoting noAxioms
I agree that the answer depends on which reference frame is present and so may be considered as ambiguous. However, why do you say that presentists don't have this problem?
Quoting noAxioms
Are your tonsils part of "you" in 2000 or not? If not, then the whole presence of "you" in 2000 does not include your tonsils. There is no contradiction.
Quoting noAxioms
Are "you" a 3D object that is wholly present at each time or are "you" a 4D object temporally extended over time? If you're a 4D object then a temporal part of you is home at noon and a different temporal part of you is at grandma's house at 1.
Quoting noAxioms
What I meant was that the given definition of motion is only logically consistent with 3D objects, and that it is logically inconsistent with 4D objects (and their parts). Since each 3D part (of a 4D object) exists at a different time, then no 3D part can move or change its location over time.
Quoting noAxioms
No, it's entailed by the logic of eternalism.
The 4D object is all "you", but it's not the same temporal part (3D part/object) of you at one time as it is at another time.
If it's not the same 3D part/object at one time as it is at another time, then you can't say that the 3D part/object moves or changes its location over time. That's purely a result of the eternalist view of objects as 4D and temporally extended.
Quoting noAxioms
You still end up with different temporal parts no matter how you slice it, so my argument against motion still holds.
Quoting noAxioms
If you don't slice the 4D object, then you just have a whole, unsliced 4D object with no parts.
The slicing of spatial parts is irrelevant and therefore so are "0D events". What is relevant to the temporal parts discussion is only (3D) objects with or without temporal (4D) extension. Those are the temporal parts we've been discussing.
Quoting noAxioms
It is analogous because no 3D part of a 4D object can change its location over time, just as no part of a rigid steel bar can change its location along its own length (disregarding the possibility of a steel bar with moveable parts, etc.). If they could do so, then they would conform to the definition of motion given. I've provided an argument for why 3D parts can't move. The only reason 3D temporal parts don't conform to the definition of motion given is because they can't move. Eternalists want to treat time as a spatial dimension, so this should be no surprise.
Quoting noAxioms
Does air die/explode? It would be no different to moving the time machine to a particular location in normal time. Let's say that whatever happens to the material already present at the target destination if we moved the time machine there in normal time is the same/similar to what would happen if we moved the time machine there via time travel. I don't see understand why you are pressing this point. What difference does it make?
Quoting noAxioms
It lands on it/collides with it. What's so important about this? Surely we can imagine that the time machine can arrive safely. I'm not interested in defining "safely". I've already said that the machine and its contents can be destroyed, but let's assume it has the technology to avoid it.
Quoting noAxioms
Perhaps, but the person who travels backwards the furthest still survives, and time travel is still logically possible. You seem more concerned about the ramifications of time travel - the end of humanity or the destruction caused by the time machine - than you are with the possibility of time travel.
Quoting noAxioms
I would refer to the one that time travelled as the original, since there cannot be two versions of a person existing at the same time without a time travel event.
Quoting noAxioms
In your previous post, the first Alice lands exactly on the second Alice, so let's stick with that.
Quoting noAxioms
According to my convention, Alice1 is the original; the time traveller. Alice2 is the 30-seconds younger version of Alice1 who exists in the past (just as young Bob exists in the past of time traveller old Bob). I cannot see how both:
(i) Alice1 will time travel back 30 seconds after crossing the tracks; and
(ii) Alice2 will time travel back 30 seconds, 5 seconds before crossing the tracks.
If Alice2 is the 30-seconds younger version of Alice1 and if Alice2 time travels 5 seconds before crossing the tracks, then Alice2 will not proceeed to cross the tracks, as Alice1 does, and will not time travel after crossing the tracks, as Alice1 does.
However, Alice2 must do exactly what Alice1 does up until (30 seconds before) Alice1 time travels, because Alice2 is just a 30-seconds younger version of Alice1. There are not two version of Alice existing at the same time until Alice1 has time travelled.
If Alice1 lands on and kills Alice2 following Alice1's time travel event, then Alice2 cannot time travel. Alice2 cannot time travel before Alice1 lands on her because Alice1 is the original time traveller; the first one to time travel. And, if Alice2 dies without time travelling, then there is no Alice3.
Quoting noAxioms
I'll try and get back to this at a later time.
Two of the three imply motion. Motion is not the fundamental difference since both have it. I've said repeatedly: the fundamental different is that presentism posits a preferred moment in time, and eternalism doesn't. That, and only that, is the fundamental difference. All the rest just follows.
The perdurantist position seems to very much be about parts, yes. That's for the perdurantists to defend. I've posted some inconsistencies I've found with that.
OK, I think I did misread that. The question comes down to then: Is there a difference between somebody claiming to be endurantist and claiming to be presentist? There are several forms of presentism, so perhaps endurantism is but one of them, perhaps 3D presentism, as opposed to growing block, spotlight, and other 4D versions of it.
Yes, I withdraw that. The concept of a worldline implies 4D spacetime, and 3D presentism does not have meaningful worldlines, but 4D versions of it do still have worldlines.
Actually, there is no Andromeda paradox under presentism, in any of its forms. Presentism denies both premises of special relativity: 1) Physics is the same in any frame. Well, it isn't. The whole point of presentism is a preferred frame, and all the others are wrong. 2) Speed of light is the same in any frame. Under presentism, that's false. The speed varies depending on which direction it is going, relative to any frame which is one of the 'wrong' ones.
So with the Andromeda thing, there is only one current moment in Andromeda, and one's choice of frame has nothing to do with it. The motion of any object is irrelevant to which events are simultaneous. The paradox is a non-starter since presentism is an absolutist view. There is no 'relativity' at all.
You seem to be mixing views in that query, rendering the question meaningless. If you're asking about eternalism, then keep it to those terms. I've never heard an eternalist talk about something being 'wholly present at some time', which seems not even wrong.
That is a decent description of movement in perdurantist terms, which I find needlessly complicated. The science community never uses such cumbersome terminology to say something so simple, which is why the 'temporal parts' page was largely educational for me.
OK, then your definition is confined to a presentist view. That doesn't mean that a non-presentist must use that definition. The definition I gave works for both, and I've never seen a dictionary restrict the definition to 3D things. In short, my google query says 'move' means to change position. The shadow of a pole moves, and it isn't a 3D thing.
So per the perdurantists that use that sort of language, 'you' change position over time, but the parts don't. It's still you doing the moving. You're just trying to leverage your private definition onto a view that defines the word differently, which of course makes it contradictory. But that's a straw man fallacy.
Remember that the two views are fundamentally identical except for that one extra premise of an additional entity. So the two views can use all the same language so long as no reference to that additional entity is made (B-series language). If such a reference is made (A-series), then it is a presentist statement only. So saying 'Floyd moves from home to grandma's house over that hour' works just fine in both views because no reference to that additional entity is made.
I don't know what purpose you think is being served by trying to argue otherwise.
Yes, but one slice can be at gradmas house and another (at the same time) is not, so I find it to be a problem. The 3D things posited to 'exist at a time' are ambiguous without also positing a preferred frame.
Not true actually. You just need to slice it the right way.
This implies that all the points of a steel bar are at the same location at a given time. The bar changes its location over length instead of a change in location over time. This fits the definition of change, if not motion. Other examples of change not over time: The air pressure changes with altitude.
Just saying...
No, but I do if I'm suddenly in the same place as air that wasn't there just before. If the machine is nothing but an air-filled balloon, then suddenly twice the air would be in there, and it might very well explode from the extra pressure.
No, that is coming from one side, pushing aside what was there. OK, so maybe it pushes stuff aside. In what direction? Does it do it instantly? That would be a nuke explosion. So it takes time, perhaps expanding outward from a point, which will certainly destroy a Delorean inside of which this growing object suddenly appears. But in such a case, the new machine is alive, and any object already there is shoved aside, possibly crushing or exploding it. The tree would not take it well, and the remainder would probably fall and crush the machine that just teleported under it.
Doesn't work since the form physics is normal motion, say from one side. Where does that start? From how far away does it effectively come? If it comes from a side, then somewhere it has to initiially appear, and not come from even further to the side. So far, the answer is that it teleports in somewhat off-center of target (destroying whatever is there), and then forcibly moving over to the actual target spatial location, possibly pushing/crushing the additional objects that are there, and of course crashing your own machine, since a vehicle collision is what happens when two things move into the same location in normal motion.
Sorry if I'm ragging on the answer, but I need to know how it actually appears. If the machine pops fully into existence somewhere (off to the side or not), it needs to deal with the material already there. If it starts at a point and expands gradually outward, then that solves the whole expel at infinite-speed problem, but it also destroys anything inside of which the expansion takes place. And if it takes time, how long? Does it slowly grow into existence over a minute? A second? 9 months?
The Alice story cannot proceed without knowing this. Also the extreme example of setting your machine to go back half a second.
No we can't. My examples are specifically designed to reduce the odds of safety to zero. I'm finding flaws in the view envisioned, which I thought was the purpose of all these posts. The half-second just is obviously going to lang on the machine that is there. Destroying it isn't such a bad thing in that case, but I need to know if that's what happens. If the jump finds somewhere more (but not completely) 'empty' nearby, would it teleport there instead? That's a different solution than the bang-and-push thing you described before. It results in different problems.
What does it do to avoid it? Go to the moon instead? NASA would love it if your machine did exactly that. So much effort saved. Who cares that it's a time machine. It's also a space teleporter.
But the possibility of time travel, as you describe it, has exactly those ramifications. If you don't want that, then a different model should be assumed.
Alice 1 has already traveled and will not do so again. Alice2 will travel back when she gets to the track, cloning everybody on that timeline, so I guess Alice1 vanishes as does everybody not in a machine that goes back in time.
Alice3 is 30 seconds away from the tracks, and has never traveled. Alice4 is at the crossing, a clone of Alice1 that did the first travel. (I neglected to name here Alice4 in my prior description, but by your convention, two new Alices get created when Alice2 goes back. So Alice2 and Alice4 collide at the tracks, and what happens thereafter depends on your collision resolution description that you're reluctant to describe. Alice3 will get to the scene in 25 seconds, and based on what she finds there, she may or may not decide to just wait for the train, or go back more than 30 seconds to avoid the accident scene, or some other choice.
I don't like your identity convention since it clones everybody in the universe except the occupants of the machine, but I am using your convention above.
Everybody time travels at noon+30 seconds, back to exactly noon. At noon+25 seconds each virgin Alice gets to the tracks and has 5 seconds to assess the situation and decide to go back 30 seconds or not.
Maybe. She makes it to the crossing too late, hits the button, goes back 30 seconds, and if her collision with Alice4 isn't noticed, she probably considers it mission accomplished and proceeds to cross the tracks just before the gates start coming down. But I don't think the collision will go unnoticed, which likely will effect whether she proceeds across the tracks or not.
Alice1 is the first to jump, and lands on nobody. She proceeds across and is truncated out of existence when Alice2 pushes her button. Alice1 is the only happy Alice, so it's a shame her life ends so abruptly.
I didn't realise there were two different definitions of 'happens'. What is the eternalist definition of 'happens'? Can you clarify how it is distinct from the definition of 'exists'?
Quoting noAxioms
Endurantism is not a form of presentism, it is a theory of how objects persist over time. However, it is entirely consistent with presentism because it holds that objects are wholly present whenever they exist, and presentism holds that only present objects exist.
Quoting noAxioms
Presentism is also a theory in its own right, which you could call "3D presentism", I suppose, or simply "presentism". That's the theory I am referring to whenever I use the term 'presentism'. I don't use the term "presentism" to refer to any "4D versions of it".
Quoting noAxioms
Agreed.
Quoting noAxioms
Objects lack temporal extension under both presentism and endurantism. Both theories face the same problem if there are two or more frames of reference (or "present moments") involved.
Quoting noAxioms
The question was basically asking if you are a presentist (endurantist) or an eternalist (perdurantist). That's not "mixing views", nor is it a meaningless question.
Quoting noAxioms
The definition of motion is confined to a presentist view, I agree, and that's because it is inconsistent with the 4D objects/parts of eternalism, as my argument shows.
Quoting noAxioms
The shadow of a pole is caused by the movements of the sun (probably) and the pole, which are 3D things. But none of them moves in an eternalist universe.
Quoting noAxioms
The motion of 3D objects is what we typically mean by "motion" (or change in location over time). I have been considering the (im)possible motion of 3D parts of a 4D object only because it is most comparable to the motion of 3D objects.
You seem to be forgetting that, according to your own eternalist view, "you" are a 4D object. In order for a 4D object to move, additional dimensions would be required, including at least another temporal dimension. If you want to argue that 4D objects move, then that's a whole other discussion.
Quoting noAxioms
I'm not using any private definition. I'm using the same definition of motion you gave earlier.
Quoting noAxioms
According to presentism, Floyd is a 3D object that changes location over time.
According to eternalism, Floyd is a 4D object that has different (3D) parts existing at different times.
It is simply inconsistent with your own definition of motion to maintain that some 3D part of Floyd can change its location over time, given that all the different 3D parts of Floyd exist at different times and none of them ever changes its location. Which part of the following argument do you disagree with?
An eternalist universe contains 4D objects
4D objects are divisible into different/discrete 3D parts
Each 3D part of a 4D object exists at a different time
No 3D part of a 4D object exists at more than one time
A 3D part must exist at more than one time in order to be able to change over time
No 3D part of a 4D object can change over time
No 3D part of a 4D object can change its location over time
Therefore, no 3D part of a 4D object can move, according to the given definition of motion
Quoting noAxioms
You cannot have two temporal slices at the same time.
Quoting noAxioms
Could you explain further?
Quoting noAxioms
I was drawing a comparison between a 3D (lack of) change in the 4th dimension (time) in the case of 3D parts, and a 2D (lack of) change in the 3rd dimension (length) in the case of the steel bar. So, I understood that the steel bar example wasn't a change over time. That's why it was an analogy.
Quoting noAxioms
I'm not interested in the physical possibility of time travel. I'm not trying to build a time machine. I'm interested in the philosophy of time, and the implications on the different theories of time. Let's just assume that it can actually transport people from one time to another.
Quoting noAxioms
I've said several times that they both die. Why won't you accept it?
Quoting noAxioms
That's one way of looking at it, I guess. But it also overwrites the timeline and deletes the timeline that the traveller departs from. I wouldn't call that cloning. The only one being "cloned", or the only one who has two versions of themself in existence at the same time, is the time traveller.
Quoting noAxioms
Where did Alice4 come from? Alice1 is still Alice1 after she time travels. She is the original. Time travelling does not create a clone of the time traveller (as a time traveller). The "clone" is the younger version of the time traveller who already exists in the past. If it helps, you can think of young Bob as the "clone" and old Bob as the time traveller.
So it is Alice1 who lands on Alice2 and they die as a result, and then the timeline continues without any Alices.
'Exist; has somewhat different meaning in mathematics, e.g. a positive integer is not prime if there exists a positive integer other than itself or 1 that divide the number evenly.
I could probably craft one that excludes the undesirable presentist view, but doing so wouldn't in any way constitute evidence that a view excluded is wrong.
Then time travel isn't possible under that definition of presentism since it would constitute travel to some destination that doesn't exist.
I do, because all of the alternate versions still posit a preferred moment in time, which is the fundamental different between any of them and eternalism.
Presentism doesn't face this problem, because only at most one of those frames can be correct, and probably neither are.
Eternalism doesn't face the problem since the phrase 'present moments' is meaningless.
I try not to hold hard beliefs. I know both, and can discuss either. The purdurantist wording seems silly to me. I've never seen its terminology used in any practical discussion, such as in the science community. And science definitely uses both eternalism (especially in a discussion of cosmology, relativity, physics, chemistry), and presentism (astronomy, climate science, biology, anthropology). I never hear anybody use 'temporal parts' or 'wholly present'. One context uses B-series terminology, and other contexts use A-series.
No, your definition is thus confined, worded specifically to exclude a view you find undesirable. 'The definition' : 'to change position' isn't so confined.
No, a purdurantist universe contains this. Don't confuse the two.
It does not follow that the lack of motion of a 3D 'part' implies the 4D object does not meaningfully exhibit motion.. At no point in any of that do you mention that the 4D object has one location at a given time, and a different location at a different time (which is how an eternalist would word it), which is, by definition (not by your definition), motion. The 3D references are perdurantist phrasing, and the argument above is still doesn't demonstrate that the object doesn't move, only that a specific temporal part doesn't, which of course it cannot since it would need time to do the moving.
Nonsense. That's what a frame change is, slicing through the same point (a given event, which has a specific time) at a different angle, which makes for two very different temporal slices. I take it by this that you're entirely unfamiliar with Minkowskian geometry.
If I slice a 4D object across a spatial axis instead of across the time axis, I end up with a 3D object that has one temporal dimension and two spatial dimensions. The location in 2D space changes over time.
My example would be a car in a drivers-ed parking lot course, sliced through z= half a meter above the lot. That reduces the 4D car to a 3D object that moves over time. It gets weirder if the driving course has hills in it.
How it handles collision is critical to identifying the implications. If I don't know how the machine handles targetting an event where there's already something else, then we cannot explore the implications of a trivial situation where that necessarily occurs.
You change the story several times, so I wasn't sure which you had settled on. OK, so they both die, Alice3 comes upon the death scene and perhaps doesn't decide to add herself to the wreckage, and chooses to miss her important appointment instead. The universe doesn't end (this time).
Your machine is very dangerous then, since it seems to require one to place a bet that the destination selected is free of anything larger than dust. It might succeed the first few time, but travel to millions of years ago? Due to erosion and plate techtonics, the destination is almost certainly in the middle of bedrock somewhere, or is way in the air, under water, or even in space. Unless the vehicle can deal with those situations, the traveler dies.
There's four Alices,. Sounds like cloning to me.
That was the convention I had initially chosen. We switched to yours. My convention had only three Alices (not four), and everybody else (Alice or otherwise) was an original. In a way your convention is better, because each person (traveler or not) has a unique history. My convention has a given person (the guy mowing his lawn nearby say) multiple histories that play out in different ways, which violates identity rules.
Clone of Alice1, made by the travel of Alice2. Alice4 lives but a moment and is gone in the collision with Alice2. Alice2 lives 30 seconds, and dies in collision with Alice4. I did say that Alice1 is the only happy Alice. It sucks to be any of the others.
Right. Her travel creates Alice2. Alice1 never time travels again. She lives but 30 more seconds and is truncated into oblivion.
No, Alice2 lands on Alice4. Alice1 doesn't land on anybody, which contributes heavily to her being the happy one.
Well, 1 is gone, 2 and 4 die in a crash, so only Alice3 survives (if she chooses to lay off the button). If she still hits the button (but in a different place than where the wreck is, and for maybe a different jump than 30 seconds, then she can make a whole bunch more dead Alices, herself included, since no actual traveler survives the experience.
True, but time travel is also not possible under eternalism since nothing moves in a 4D universe.
Quoting noAxioms
Fair point. Presentism is a theory of existence, whereas endurantism is a theory of persistence. Therefore, I suppose you're right that endurantism is not positing the existence of any present moment (or of objects at any present moment), but instead says only how objects persist. The way that objects persist according to endurantism is entirely consistent with there being a present moment, since those objects are said to have no temporal extension and are wholly present whenever they exist.
Quoting noAxioms
No, there is no motion in an eternalist universe, as I have argued. Therefore, the definition of motion is only consistent with a presentist view.
Quoting noAxioms
An eternalist (block) universe is 4-dimensional by definition, and so are its objects.
Quoting noAxioms
A 4D object could only possibly move in a higher (e.g. 5th) dimension. A 4D object does not "meaningfully exhibit motion" because no 3D part of it can ever change its temporal or spatial location.
Quoting noAxioms
Surely you mean that a 3D part of the 4D object has one location at a given time and a different 3D part of the 4D object has another location at a different time. You need to explain how two different 3D parts of a 4D object can produce the change required for your definition of motion, when neither of those 3D parts ever changes its temporal or spatial location in the block universe.
One can easily just assume that one or more of those 3D parts can move, but it's not consistent with the static nature of the 4D block universe posited by eternalism. To simply assume there can be motion in an eternalist universe, while telling me I'm wrong without actually addressing my argument, is begging the question.
Quoting noAxioms
Okay, but which preferred method of slicing allows for a 3D part of a 4D object to change its temporal or spatial location?
Quoting noAxioms
What you say "was the convention" is my convention; that's what I'm telling you. Whatever you switched to isn't mine.
Quoting noAxioms
Alice2 can only clone herself. What makes you think she clones Alice1?
Your scenario, as I now understand it, is that Alice1 time travels backwards and "clones" Alice2, such that Alice1 and (Alice1's younger self) Alice2 now co-exist at the same time. If Alice2 now time travels backwards, then she will clone Alice3 (Alice2's younger self) and Alice2 and Alice3 will co-exist at the same time. Alice1 will no longer exist, just as all the people on the timeline when old Bob departs and time travels backwards no longer exist. That's what it means to overwrite the timeline; the timeline reverts back to its earlier state at the traveller's arrival time, except that that time now also includes the time traveller and their time machine.
According to the article you linked, both are alternate interpretations of persistence. Despite what various articles might call them, neither is a theory since they both lack any empirical falsification test.
And I've shown otherwise, so you're simply wrong. The eternalists use all the same language as do the presentists, but formally, only references to the nonexistent extra thing is what makes a statement meaningless. Motion has meaning under eternalism since a statement such as 'Floyd takes an hour to move from A to B' has meaning.
Really, why the brutal discrimination here? What purpose is served by your refusal to accept normal usage of language? You seem to seek only to prevent people that hold an alternate view from being able to discuss anything, when clearly the statements have meaning.
That wasn't so hard, was it?
It produces motion by exactly fitting the (not my) definition: Floyd is at one location at one time, and a different location at another. Floyd moves even if what a perdurantist calls his temporal parts do not.
Any slicing does this. The positing of a preferred way is known as 'absolutism'. The first premise of relativity is that there isn't a preferred way, but it's a premise, meaning relativity isn't proof against a theory that doesn't accept that premise. The slice can be odd shaped. It need not be flat, but it does need to be space-like, else you end up with events that occur out of causal order.
All the Alices are herself, and Alice1 made it across the tracks without crashing. Alice4 dies immediately upon coming into existence, and is the shortest-lived Alice.
If your convention is that only Alice2 gets cloned, then I suppose Alice4 and Alice1 are just Alice1, who experiences two different fates, a contradiction of identity. X crosses the tracks. X does not cross the tracks. That violates the law of non-contradiction, and the problem is solved by differentiating Alice1 and Alice4.
It's all a nitpick what names we give them. The scenario was solved. Time travel is super dangerous. Can we move on? There's so many more problems to discover.
Mostly right. You didn't mention the Alice that collides and dies with Alice2 in that description (so 3 Alices coexisting at once, but two of them dead). The time machines were cloned as well, so there were 4 of those, one truncated away, two crashed into each other, and the only one remaining is the one never used.
I think you've misread. I said presentism, not perdurantism.
Quoting noAxioms
Huh? No, it wasn't hard to correct you.
Quoting noAxioms
You are again assuming that Floyd is a 3D object. However, under eternalism, Floyd is a 4D object. One 3D part of Floyd is at one location at one time, and a different 3D part of Floyd is at a different location at another time. Both 3D parts of Floyd co-exist at two different times. In fact, each 3D part of Floyd exists at a different time and all 3D parts of Floyd co-exist. Therefore, no 3D part of Floyd changes its temporal (or spatial) location. However, a 3D part of Floyd must change its temporal (or spatial) location in order to meet the definition of motion.
Otherwise, you could argue that what moves is Floyd as a 4D object (or some 4D part of Floyd, or the block universe as a whole). However, that would require higher (e.g. 5th, 6th, etc.) dimensions in which the 4D part/object/universe can move. This is not comparable to the motion of 3D objects.
Quoting noAxioms
How does any method of slicing allow for a (post-sliced) 3D part to change its temporal or spatial position?
Quoting noAxioms
How does Alice4 (Alice1's clone) come into existence? You say it's a result of Alice2's time travel but you haven't explained how.
I guess I'm not clear on the difference between the two. Both are essentially ontological stances, which is in the end, existence. 'Persisting through time' and 'existing in time' seem to be just different ways of saying the same thing, so perhaps I'm missing an important distinction.
But I never disagreed with the 'corrected' statement.
I never said any such thing, in the context of eternalism. The 3D things are (per the perdurantists) separate 'parts' of the 4D thing. It is the 4D thing said to move (change locations over time), not the parts.
I gave an example where this wasn't true, but I know what you mean. To summarize, by definition, no event that is part of Floyd can be at different coordinates in an inertial coordinate system. It's true of a 0d event, even if not necessarily true of 'parts' consisting of 1-3 dimensions. But motion isn't defined as an event having more than one set of coordinates. It is a difference of location at different times, and Floyd meets that definition.
To meet your discriminatory definition maybe. Floyd is home at noon and at grandma's at 1. That is motion by the definition. That's how the language is used by an eternalist. The language is serving its purpose, which is to have meaning, and it does so without needing to change the definition from 'change locations over time'.
The 'over time' part is necessary, because my one hand is at a different location than the other, at one given time. That isn't motion of Floyd. It's a difference in location of parts, sure, but not over time. Extension alone is not usually considered to be motion.
Do you understand a 3D cross section of a 4D object? All the events on the arbitrary slice can be assigned the same time coordinate so long as the slice is space-like. Angle the slice a different way and a different set of events (except those events at the intersection of the different slices) are now assigned the same time coordinate. This is essentially a change of reference frame, coupled with relativity of simultaneity, with which I suspect you are not familiar else you'd not be asking that question. A loaf of bread is often the analogy (slicing a 3D object, with time being the long dimension say) along 2D spatial planes, arbitrarily oriented. A slice through a given event (the center of the loaf say) can be angled in many ways and still include that one event, so all the other events are only part of some slices and not part of the others. That's relativity of simultaneity in bakery terms.
I bring all this up because perdurantists seem to slice Floyd up into 3D disjoint parts, but that can only be done if there is a preferred frame. If arbitrary frames are allowed, 3D cross sections can intersect (be in different locations at 1 given time), and I don't think perdurantists intended that. So without resolution of this issue, they seem to require a preferred frame (absolutism, without the presentism), which violates the relativity theory of which they're presumably in favor. A change in location over frame rotations (instead of over time) is also not considered to be motion by most, but the change in location can be quite large.
You can probably tell that I'm not impressed with the perdurantist shtick.
Alice1, at the tracks at t=12:00:30 travels back 30 seconds to being there at exactly noon. So Alice1 is at the tracks at noon. Alice2, at t=12:00:30 also selects that same noon event as her destination, so she clones the Alice1 there and the first-noon version of Alice2 (not at the tracks), to create two new clones Alice4 and Alice3 respectively. Alice 2 and 4 are occupying the same space at the tracks simultaneously, and one doesn't survive that.
Do I have to explain it yet again? I don't know if I can get any more detailed.
As I just explained:
Quoting Luke
You are treating Floyd as a 3D object, not as a 4D object. That is not consistent with eternalism.
Since the 4D object as a whole does not move (or since such higher dimensional motion is irrelevant to our dispute), and since no 3D part of a 4D object can ever move, then there is no motion in an eternalist universe.
Quoting noAxioms
Yes, motion of a 3D object. No 3D part of a 4D object can ever be at a different location or time other than the location and time at which it eternally exists.
Quoting noAxioms
No, that’s how the language is used by a physicist who ignores the internal logic of eternalism.
Is velocity also forbidden then? I mean, velocity in block view is either a rate of change of position over time (generic definition), or it is the slope of the object's worldline (an alternate definition that is not compatible with 3D presentism).
The constant c apparently has no meaning in physics. Hmm... Somebody ought to tell them that they're all talking bunk.
The conversation has ceased being about time travel. I apparently cannot discuss an eternalist view with all the restrictions placed on language, all under the guise of 'logic'.
You refuse to acknowledge that Floyd at noon is but a 3D part of a 4D object.
Quoting noAxioms
Technically, Floyd-at-noon and Floyd-at-1pm are two different 3D parts (of Floyd the 4D object).
Quoting noAxioms
It is all still Floyd the 4D object. But it is not Floyd the 3D object, which departs grandma's house at noon and arrives home at 1pm. That's because both (noon and 1pm) parts of Floyd co-exist. The noon-part of Floyd doesn't change its temporal or spatial location, like you assume. You appear to suppose that a 3D part of Floyd departs from its temporal and spatial position at noon and then arrives at (and replaces?) the 3D part of Floyd that exists at 1pm. (Not to mention all the 3D parts that exist between noon and 1pm.)
Quoting noAxioms
Floyd is a 4D object. The differences over time that you refer to here are between different 3D parts of Floyd. Those 3D parts all co-exist. It is not - as you suppose - Floyd the 3D object at one time and then Floyd the same 3D object at another time. It is only a 3D part of Floyd existing at one time and then another, completely different 3D part of Floyd existing at another time. Those 3D parts are not the same 3D object; they are two different 3D parts co-existing at different times. The first 3D part does not move from its temporal location at noon to (replace?) the second 3D part at its temporal location at 1pm. Instead, each 3D part exists at its own time and never moves.
The definition of motion is a change in a 3D object's position over time. This definition does not apply to two diffferent 3D objects or to two different 3D parts of a 4D object; it applies to a single, enduring (same) 3D object over time.
Quoting noAxioms
Generally speaking, no. But in an eternalist universe, yes. Nothing moves in an eternalist universe.
Quoting noAxioms
I never claimed anyone was talking bunk. I'm only saying there's technically no motion in an eternalist universe. This needn't imply that there's no motion in our universe, only that if there is motion in our universe, then our universe is not (purely) eternalist. You are borrowing presentist concepts when you treat 4D Floyd as an enduring 3D object over time, which can change its location between noon and 1pm.
I do acknowledge that the perdurantists would say that Floyd at noon is a 3D part of a 4D object. I don't really approve of that for several reasons, all of which I've stated, but ambiguity being a big one.
I will also say that, given a frame of reference to define the hyperplane of simultaneity referred to as 'at noon', then 'Floyd at noon' defines a set of events that comprise a 3D spatially extended region, and that those events are a subset of all the events that are considered to be Floyd.
That's pretty close to the perdurantist wording, but without all the ambiguity and terms with loading meaning. Funny thing is, the statement works under presentism as well, except the specification of the frame wouldn't be necessary.
There you go again, putting straw man assumptions in my mouth.
And reiterating discriminatory definitions as well. I showed that definition to be false even in presentism (the shadow), and you didn't counter it, but rather came up with irrelevant comments about its causes.
So you've proven what nobody seems to be able to do, which is to falsify eternalism. Kindly detail some empirical falsification test, Love to hear it.
So far I have: There is obviously motion. Eternalists are not allowed to use the word, therefore, by language offense, eternalism is false. It doesn't fly because it isn't an empirical falsification.
The topic has been abandoned altogether, and communication about this side track seems hopelessly mired. I think I will step out at this point.
Do you at least acknowledge that Floyd is a 4D object according to eternalism? A 4D object requires higher dimensions within which to move, but that’s not the sort of motion you describe in your Floyd example.
Quoting noAxioms
What exists in a presentist universe is continuously changing. 3D objects can change their location over time in a presentist universe even if presentists cannot measure that change or do not acknowledge the existence of any other times.
Quoting noAxioms
It depends what sort of object Floyd is. Are you talking about the "states" of 3D Floyd or of 4D Floyd? Your previous descriptions indicate that it is 3D Floyd who supposedly moves. For example, you are presumably not talking about changes in 4D Floyd's spatial location(s), but about changes in 3D Floyd's spatial locations at different times. If 3D Floyd is what you call a "state" of Floyd, then yes, no 3D part/state of 4D Floyd changes its location or moves. 3D Floyd is not earlier at time t[sub]0[/sub] and then later at time t[sub]1[/sub], because two different 3D Floyd parts co-exist at each of those times. 3D Floyd doesn't change his location between those times because there exists more than one 3D Floyd at, and between, those times.
Quoting noAxioms
Okay, but there is still the assumption that the same 3D Floyd object changes its location over time. In order for there to be motion, an eternalist must ignore that more than one 3D Floyd object exists over that time.
Quoting noAxioms
If you don't assume that Floyd-at-noon is the same 3D Floyd object as Floyd-at-1pm, then how could you coherently refer to it (i.e. Floyd the 3D object) as having changed its spatial location (i.e. as having moved) or not? You must assume that the noon-part of Floyd changes its spatial and temporal location in order for it to move.
Quoting noAxioms
Okay then, an object with less than four dimensions. It's still either the same shadow that can change its spatial location over time (per presentism) or else it’s many different shadows that cannot change their spatial locations over time (per eternalism).
I will continue to refer to 3D objects instead of "objects with less than four dimensions" though, only because I assume 3D objects are much more common.
Quoting noAxioms
No empirical test is required. It's what eternalism logically entails.