Is time travel possible if the A theory of time is correct?
Suppose that the metaphysics behind the A theory of time is correct, is it possible to travel to the year 2024 (or the "future") or the year 2000 (or the "past") or does time travel require the B theory of time to be correct?
Under the B theory of time, all points in time are ontologically equivalent and asking if one can travel to the year 2000 or 2024 is like asking if one can travel to the Moon or to Mars and I think that this makes it obvious that if the B theory of time is true, then time travel is at least metaphysically possible; however, regarding the A theory of time, the following is true: the present is metaphysically privileged and becoming is a real feature of reality.
So is time travel possible if the A theory of time is correct?
Under the B theory of time, all points in time are ontologically equivalent and asking if one can travel to the year 2000 or 2024 is like asking if one can travel to the Moon or to Mars and I think that this makes it obvious that if the B theory of time is true, then time travel is at least metaphysically possible; however, regarding the A theory of time, the following is true: the present is metaphysically privileged and becoming is a real feature of reality.
So is time travel possible if the A theory of time is correct?
Comments (284)
Firstly, it depends what you mean by the A theory and the B theory of time. Presumably you are using these as synonyms for Presentism and Eternalism (respectively), in which case you are talking about the ontology or existence of time(s).
There is also the [McTaggart's] A-series and B-series of time, which refer to a temporal ordering of events, but that's not important right now.
I will use 'A theory' as a synonym for Presentism and 'B theory' as a synonym for Eternalism below.
The B theory holds that all times (and everything at those times) exist...equally. Therefore, those times are available travel destinations, if we are to assume that time travel is possible.
The A theory holds that only the present time (and everything at that time) exists. Therefore any time other than the present time is not an available travel destination. This appears to rule out the possibility of time travel according to the A theory.
However, there is one caveat, which is that the present time is always moving into the future.
Exactly. So, presentism doesn't exclude all time travel. I don't see why presentism as such should be inimical to other kinds of time travel, proceeding at different rates than the normal forward rate.
Time travel is not possible according to presentism because those other times (or travel destinations) do not exist (according to presentism). I did not get into it in my previous post, but the caveat I spoke of there (that the present is always moving into the future) can only be viewed in terms of the B theory. According to presentism, no future or past times exist nor any other time except for the present time, and therefore time travel is not possible by presentism's own lights. Any time travel, including time travel at the "normal forward rate", can only be viewed in B theory terms. That is, unless you mix or disregard the tenets of the A and the B theories, because obviously we can and do talk about other times and probably nobody is a true presentist.
So why did you start the B-theory thread about free will and then totally abandon it? It degenerated into the usualy discussion of what eternalism is rather than its implications.
Travel to 2024 is simple. Just wait 5 years or less and the passage of time will take you there. Of course, it's past travel is where things get tricky. If one assumes presentism, then there is no time that exists apart from the one that we are in in 2019. Because there exists no year 2000 destination to travel to, then it's impossible to really "travel" to 2000 like you would "travel" to France for vacation. But that doesn't mean you can't create your destination. Just think of the universe as if it were a movie playing on a VHS, and hit the rewind button. Give it 19 years and soon you'll find youself in the year 2000. Simple as that. No extra times or 3D universes required and everything is kept in the present.
Wouldn't it be necessary to have very clear principles of exactly what eternalism is, before we can determine its implications? If we can't agree on those principles, discussing implications is sort of meaningless. One could just change the principles of what eternalism is, to produce favourable implications.
There are certain space-time structures that make time-travel possible, if I remember correctly. Didn't Kurt Godel discover one, as did Frank Tipler?
Also there is a theory of time -travel in the multiverse, the catch being that the time you go to will not be in your world.
Presentism is wrong according to these theories.
What do you mean?
Thinking a bit more about this, if now is an objective fact on presentism, and the Time Traveler is transported some ways into the past or the future, what happens with the now? The situation is different from the normal "time travel" when everyone moves forward into the future in lockstep at 1 second per second, because the Traveler has left everyone else in the future (or the past). The only way this makes sense to me in the presentist framework is if now splits into two nows: one travels with the Traveler (where it entangles everyone else in his present) and one stays with his former contemporaries and continues on at its usual pace.
Note that these considerations are quite apart from the question of existence of the past and the future (which, frankly, make little sense to me).
I presume you ride the 'now' into the future. That's how it worked. To travel to the past, I suppose you'd have to get time to go the other way, and still be able to ride it, but leaving everybody else behind.
In more objective terms, I think time travel to the past would be to cause an instance of 'yourself' to exist at time X, but with memory of time Y, with Y > X. This is pretty easy to do in theory in the forward direction, but not so much backwards, being a violation of the principle of locality.
Quoting SophistiCat
I always wondered what meaning there is being a unit of X per X, which seems to reduce to just unitless '1'. On the other hand, our clocks are dilated mostly due to the gravity well in which we find ourselves, so maybe the rate is still unitless, but still less than 1. How much less is an eye-opening exercise.
Not any spacetime structure that's correct, though. I'm not saying that it's not a popular belief that time travel is possible, but the belief rests on not understanding what time really is.
But the Multiverse structure is correct.
You may be right.
To offer some explanation and defence of my view, I consider there to be a perfect symmetry between the motion of Presentism and the motionlessness of Eternalism. Presentism, with its present moment ever flowing into the future is how we experience time, whereas Eternalism with its motionless ontological equality is how we represent or model time. Both are required for our understanding of time. Without the eternalist picture, there is no model or representation of time and we cannot even talk about time. Without the presentist picture, there is no motion and thus no time at all. They need each other. Anyway, that's my probably ill-conceived view in a nutshell. I would consider naming it 'Dumb Presentism', but too many might agree.
In my previous post I argued that only the present time exists according to presentism and that no other times exist. I expect an easy rebuttal to this would be, e.g., that future times don't exist now but that they will exist (or may exist) when they come into existence. Likewise for past times: that they did exist even though they no longer do. Fair enough, but I still like the symmetry of my view. Donning my pure presentist hat for a moment, I might even respond: what other times are you referring to?
One consequence of my view would be that even if the presentist did time travel (to some abnormal temporal destination), then they could be oblivious to having done so because it would always remain the present time for them anyway.
lol
Quoting noAxioms
This works for the Traveler, but what about the rest of us? What happens to us and our now when the Traveler departs into the future or the past, and now departs with him?
Quoting noAxioms
We can imagine a world in which, in the year 2019, you stepped into the time machine and suddenly disappeared. Earlier, in the year 1919, an exact copy of you as of 2019 suddenly appeared in a field, fooled around for, say, a week, and then disappeared. Meanwhile, in the year 2019, five minutes after vanishing in the time machine, you reappear, having the memories and other physical changes that your copy had in 1919 at the time of disappearance.
We could tell the same story chronologically, without jumping back and forth between 2019 and 1919. The reason we usually tell these stories achronologically is to emphasize causal connections. But in this telling there are no anomalous causal connections between the past and the future - and that is why it does not count as time travel. Time travel is all about anomalous causality.
Quoting noAxioms
Yeah, I only invoked that formula in order to represent the difference between normal time flow and time travel as a difference in the rate of time flow (as seen from the presentist standpoint). Note that in non-inertial reference frames your local time still passes at the usual rate.
Well, they 'rewind' along with the rest of 'history', which isn't even a violation of physics. Only what you (the 'traveler') are doing is a violation.
Pretty much the standard depiction, yes. I think Back to the Future did almost exactly this.
The story typically involves a vehicle, emphasizing that it takes to 'the past' like that is a place. Nobody does it with a say a pill or scan-and-teleport with reverse causality. Tron and Star Trek sort of do the scan depiction, but to a different place, not to the past.
Some depictions just have a device like a wristwatch that does the job for you. Some depict a portal that requires a receiving portal on the other side.
I think it very much counts if there is a guy in 1919 with memory of 2019. The way you tell the story puts emphasis where the storyteller wants it, but there would be little dispute of time travel to somebody with such memories in 1919, however little he might be able to convince the locals there.
I agree, and I've never said otherwise. What I've said is that, according to my view of presentism, no other times but the present time exist, and time travel can only be viewed from an eternalist or B theory perspective of time.
How about doing a simple time dilation experiment? Synchronise atomic clocks, and take one on a flight around the world. When the clocks are reunited, they no longer agree on the time. How is that possible under presentism?
If time is a fourth dimension (relativity) then it becomes natural to expect an extension in it. We can move to and away from a particular location in the 3D of space, why would the 4th dimension of space be excluded from such a possibile property?
The question that bothers me is why are there no instances of time travel? Why is it difficult? We see travel in 3D space - it's so commonplace that no one even notices it. What is so special about the 4th dimension?
Are both clocks at the present when they are reunited? The time displayed on the clocks is irrelevant to presentism, so long as the clocks always remain at the present.
If the "Present" existed, then the clocks would read the same.
That has been done many different times and many different ways and the result is the same, clocks run at different rates under the influence of gravity and acceleration. The time reading on a clock however has nothing to do with presentism. Time is not fundamental, what is fundamental is change and process, and the rate at which a clock runs, or humans age, varies with gravity and acceleration. There is a fundamental misunderstanding about what time is (a derived concept from change) and what clocks do (they are processes that run at different rates under different conditions).
How does gravity alter the rate of clocks under presentism?
How can the present be at different times under presentism?
Why do clocks on the earth and in orbit run at different rates?
Clocks in different time zones don't run at different rates.
[i]According to the theory of relativity, time dilation is a difference in the elapsed time measured by two observers, either due to a velocity difference relative to each other, or by being differently situated relative to a gravitational field. As a result of the nature of spacetime,[2] a clock that is moving relative to an observer will be measured to tick slower than a clock that is at rest in the observer's own frame of reference. A clock that is under the influence of a stronger gravitational field than an observer's will also be measured to tick slower than the observer's own clock.
Such time dilation has been repeatedly demonstrated, for instance by small disparities in a pair of atomic clocks after one of them is sent on a space trip, or by clocks on the Space Shuttle running slightly slower than reference clocks on Earth, or clocks on GPS and Galileo satellites running slightly faster.[1][2][3] Time dilation has also been the subject of science fiction works, as it technically provides the means for forward time travel.[Experimental testing[edit]
Hafele and Keating, in 1971, flew caesium atomic clocks east and west around the earth in commercial airliners, to compare the elapsed time against that of a clock that remained at the U.S. Naval Observatory. Two opposite effects came into play. The clocks were expected to age more quickly (show a larger elapsed time) than the reference clock, since they were in a higher (weaker) gravitational potential for most of the trip (c.f. Pound–Rebka experiment). But also, contrastingly, the moving clocks were expected to age more slowly because of the speed of their travel. From the actual flight paths of each trip, the theory predicted that the flying clocks, compared with reference clocks at the U.S. Naval Observatory, should have lost 40±23 nanoseconds during the eastward trip and should have gained 275±21 nanoseconds during the westward trip. Relative to the atomic time scale of the U.S. Naval Observatory, the flying clocks lost 59±10 nanoseconds during the eastward trip and gained 273±7 nanoseconds during the westward trip (where the error bars represent standard deviation).[39] In 2005, the National Physical Laboratory in the United Kingdom reported their limited replication of this experiment.[40] The NPL experiment differed from the original in that the caesium clocks were sent on a shorter trip (London–Washington, D.C. return), but the clocks were more accurate. The reported results are within 4% of the predictions of relativity, within the uncertainty of the measurements.
The Global Positioning System can be considered a continuously operating experiment in both special and general relativity. The in-orbit clocks are corrected for both special and general relativistic time dilation effects as described above, so that (as observed from the earth's surface) they run at the same rate as clocks on the surface of the Earth.[41][/i]
The rate at which a process occurs, mechanical clock ticking, biologic or chemical is affected by the gravitational field in which it occurs. Again nothing much to do with presentism and very little to do with the nature of time itself except to show that keeping time is just measuring the relative rate of change. Time itself as we typically talk about or conceive of it does not exist. There is no absolute universal fixed time (Newton), passing at a uniform rate.
What do you mean "they rewind"? The idea of time travel is that someone (or something) is moving in time (at a different than normal rate), while everyone and everything else goes on as if nothing happened. But how this divergence is possible if there is only one now is something I can't wrap my head around. It would make sense if now diverged as well.
Quoting Luke
No times but the present exist, and wherever the present is, that is what exists. Yesterday the present was thataway, and now the present is thisaway. Nothing about presentism says that the present has to stay in one place.
Right, I've never denied that either.
Quoting Inis
Yes they do, all other factors being equal.
Edit: I read this last comment wrong. Negate this reply....
Well, I buy into neither presentism nor time travel, so I'm trying to imagine how a presentist would envision travel to a time that is no longer existent. Somehow you need to find yourself in a world with the state being some prior state except for you being in it, which sort of seems to require a physical rewind of all state (except the part where 'you' appears in it), thus dragging the present back to that prior time. It really makes no sense to me, but it makes no sense in the block view either, so go figure.
Well relativity gets you that, and it even looks normal to the 'travelling' person.
I don't think it makes sense for a presentist to propose a divergence of time. A divergence of worlds, sure. That avoids some paradoxes, but time going forward for Fred but backwards for me in my machine, no. If my machine does that, then it just creates a new world now that looks like my old world did X years ago, without actually alter the course of 'the present'.
As I said, it is actually quite easy to achieve time travel in the forward direction (clock moving at other than the usual subjective rate). You can do it with anesthesia or cryonics. The former doesn't halt aging like the latter does. They can also just manufacture a new 'you' a thousand years from now, which is possible at a biological level but probably not a molecular level, and certainly not subatomic.
The subjective experience is fairly similar for all three. You look at a clock, there is a discontinuity, and suddenly the date on the wall is different. It may or may not involve a feeling of 'waking up'. This differs from sleep where there is a definite subjective sense of how long you've been out.
None of these methods work with a negative time rate. Travel to the past is just nice fiction, despite quantum experiments that can be interpreted as cause well after effect.
Really? How does GMT+1 manage to remain +1 to GMT if the time zones run at different rates?
I don't see how the reading on the clock has anything to do with whether or not the present exists.
My bad. I read your comment as suggesting that they didn't run at the same rate.
Hey, we actually agree on a point...
I have noticed that we do agree at a few points, but then we go in different ways.
Perhaps you don't, but you cannot explain, given an objective present, why the clocks diverge.
Even if there were no clocks, the present still "exists" and change still happens and therefore time (a derivative concept of change) passes. If there were no change there would no time.
Both clocks traveled the same amount of spacetime. However since one clock traveled further in space, it therefore traveled less in time. Which is to say, it ticked at a slower rate than the clock on the ground.
I am aware of at least some of the problems of presentism (including this one), but it seems to me that presentism needs to be assumed in order to address the topic of this discussion.
In response to your question, the clocks are reunited and measured from a preferred frame of reference, so can't we also talk about presentism and eternalism from a preferred (e.g. Earthly) frame of reference, at least for the purpose of this discussion?
Time travel may not be possible, or we may not have discovered how to do it yet, but I think we can entertain the possibility for this discussion at least.
I'm not sure how this relates to what I've said. Perhaps you're just noting another problem with presentism in relation to the rate at which time flows? Again, I think we need to assume presentism (or that "the A theory of time is correct") for the purposes of the topic of this discussion. However, if you all just want to discuss the failings of presentism then have at it.
If that is the case, then the standard conception of backwards time travel of simply going back to the past is strictly impossible, because your actions from there on out will inevitably affect the present, and everything from the time you have left will not go on "as if nothing happened".
However, I don't think there is any specific definition of what time travel is, apart it being some mechanism that can get you to a world which is in "2000 AD". There are many different ways which one can conceivably do just that in fiction, some of which involve divergence (like multiverse theory) and others which don't (like simply rewinding the universe).
We know that an objective present cannot exist because the clocks disagree. All there can be are relative presents.
And presentism cannot explain why this happens, whereas eternalism has a fully worked out scientific theory called General Relativity, which explains it.
Quoting Luke
Apparently I was responding to a different quote, the one just below the one quoted in that response. It is about how time dilation doesn't invalidate presentism.
That's two posting mistakes I've made now.
Presentism and Eternalism are two different metaphyscial interpretations of the same empirical data. Since time travel would be an empirical experience, it should in principle make zero difference whether presentism or eternalism is assumed. Under current empirical physics, both metaphysical views forbid time travel to the past, and neither forbids forward travel. Hence I see little point in needing to assume one metaphysical stance when discussing if a physical act is possibility or not.
Eternalism isn't metaphysical if it's part of our best physical theories. Both general relativity and quantum mechanics tell us that the universe as a whole is at rest. This was realised early on in GR but took a while to be understood in QM.
This means that presentism isn't metaphysical either, it's just wrong.
What is metaphysical, however, is the claim that an objective observer-independent Reality exists. If you take the view that reality is observer-dependent, then presentism may be rehabilitated, but at what cost? Alternatively, you could take the view that our philosophy of time need not be compatible with our scientific theories. That seems even worse!
No clock or other device measures objective time, so this doesn't follow. All clocks run slow, and some slower than others, so it is to be expected that they don't always agree.
Quoting Inis
I don't think any of those theories assert it, despite the typical interpretation of relativity. I know Einstein held eternalist views due to the implications of the theory, but that's mostly because it is the simpler view, without a needless addition that adds nothing to the theory.
Anyway, relativity doesn't make any references to 'the present', but doesn't deny it either. It actually (reluctantly) acknowledges a preferred foliation, which can be interpreted as relativity supporting at least one aspect of presentism. Still, an objective ordering of events is not an assertion of the existence (or lack of it) of a present, which makes no empirical predictions.
I actually don't follow what you're trying to say here. I don't know what it would mean to say that the universe is not at rest (has a nonzero velocity???), so there doesn't seem to be any meaning to saying it is at rest.
Then you say this makes presentism wrong, and I don't see the connection.
I like good arguments against presentism, and I even have a unique one of my own, but I think they're all faulty.
Yes, that would be a metaphysical claim, and one independent of the eteralism/presentism debate. The latter concerns the nature of the universe (is it 3D or 4D?), but the former is something deeper, and seems to rest on a sort of undefined meaning of 'exists'. Being a relativist, I don't make sense of something being said to just 'exist'. It exists in relation to something (which need not be an observer), and I'm not sure in relation to what the universe might be said to exist or not exist. So such statements need to be defined by those that makes such statements.
If 'I' am an observation, that observation is taken at some event, and that means 'I' am an event, in relation which 'the present' very much has meaning. If 'I' constitutes a defined series of specific events, then those events are not simultaneous and none of the events is more special than any of the others, except perhaps the two endpoints. 'The present' could still be defined as the last event of the series of events that defines 'I'. Presentism is not wrong there, and the cost doesn't seem too high.
Notice that it is sort of an idealistic view. 'I' defines the present, not the other way around. That's a bit of cost I think.
The universe is like the balloon, with the galaxies painted on it, moving around a bit, but generally moving away from each other as the balloon expands. oom in and there is you and I on it.
Presentism says the the balloon is like, well a balloon, without an interior. Only the present surface is the actual part of the balloon. Eternalism says that all of the space, both interior and exterior points are part of the object. There is no surface to the thing at all, defining points that are interior or exterior. Growing block says it is a solid sphere, with an outside surface, but points outside of that are not part of the object.
I find these all to be metaphysical differences, but others do not. My claim for my stance there is that there are no empirical distinctions between these three scenarios.
The metaphysical claim that the object exists independent of observation is a different claim, and can be claimed or denied by all three scenarios. The object, whatever its nature, exists or not. Again, this is metaphysical since again, there are no empirical distinctions between these two scenarios.
A presentist need not deny observer-independent reality. Instead they are describing reality from a preferred reference frame - their own (as Luke discusses here).
That is compatible with the universe as a whole being static and unchanging (and thus a kind of eternal present independent of time).
This is similar to Alice measuring an electron in a spin up state. That is true in her reference frame. Yet that is compatible with the electron being in superposition in a different reference frame.
And someone else can describe reality from a different reference frame and they both disagree. They don't just disagree on the time, but disagree on the factual state of affairs in their relative presents.
If there exists an observer-independent presentist reality, how can "descriptions" of it be different?
In the time dilation example, one clock traveled a different spacetime path to the other. Once each clock's reference frame is factored in, there is no factual disagreement - time simply elapsed at a different rate for each clock.
What do you think "time elapsed at a different rate" means? Suppose you and I meet. It is the present when we meet. Then we go our separate ways, and meet again later. It is still the present when we meet the second time, and it was the present for each of us during the entire intermediate period. But for each of us, there is a different amount of time passed between the two meetings, if we take differing spacetime paths. Doesn't this just mean that there is not a fixed quantity of time between any two distinct points of the present? So we can say that for any two points in time, there is not a fixed amount of time between those two points, because the quantity of time between them varies according to the spacetime path that a person or thing takes to get from one to the next.
Yes.
Quoting Metaphysician Undercover
It just means there is no absolute (or frame independent) time. Here's an example in terms of the twin paradox.
Suppose Alice and Bob are twins. On the day they both turn 20 years old, Bob travels into space at high speed and returns on the day that Alice turns 30 years old (according to Alice's clock on Earth). But Bob is 26 years old (according to the clock on his spaceship) and has only aged 6 years. Less time has elapsed for Bob than for Alice. (Example here.)
Literally everything in relative motion inhabits a different present. These presents become more strikingly in disagreement as relative speeds increase and with distance. A classic example of this is Penrose's Andromeda Paradox, inappropriately named, because it is not a paradox.
So I may conclude that from the point in time when Bob left, to the point when Bob returned, the amount of time which passes is dependent on one's frame of reference. Can I make the further, more generalized conclusion, that the amount of time between any two points in time, is indeterminate?
Just curious what you're thinking there. Why would it be indeterminate?
It's indeterminate because from every different frame of reference there is a different amount of time between the two points. Therefore there is no fixed value for that time period.
It seems like you're thinking something like:
* There's a "Master Time" that overarches all other time,
* Those other times pass differently relative to each other,
therefore
* From the perspective of the "Master Time," there's an indeterminate amount of time between any two points.
Is that right?
If I assumed a "Master Time", then I couldn't conclude that time is indeterminate. The Master Time would necessitate a determinate time. So, remove your premise of Master Time. Make your perspective the human perspective. From the human perspective, there is a variable amount of time between any two moments in time depending on the frame of reference. Therefore time is indeterminate.
But time isn't indeterminate in a particular frame of reference. It's just relative--due to factors such as velocity--when you compare different frames of reference. We can predictively calculate those differences to a high degree of precision, which wouldn't make much sense if it were indeterminate.
I know, but the human perspective gives us the potential for infinite frames of reference. Therefore from the human perspective, time is indeterminate.
Quoting Terrapin Station
I can't see the point here. The very fact that there are differences in the amount of time which passes between one moment and another moment according to human measurement, is clear proof that time, which is what passes between those moments, is indeterminate from the human perspective. Unless the means of quantifying the differences provides an absolute solution, then all it does is veil the indeterminacy, hiding it behind an illusion of determinacy. Perhaps you'll understand if you consider that there is a limit, the speed of light, and as the frame of reference approaches the speed of light there is an infinitely small quantity of time between two moments. Infinite is synonymous with indeterminate.
So "psychological time"? Yeah, that's highly variable.
I never said anything about "psychological time". I'm talking about time itself. From the human perspective, time is indeterminate.
It is called a preferred reference frame, or at least a preferred foliation (an objective ordering of events). Presentism must assume such a thing, but the existence of a preferred foliation does not necessarily imply the existence of a present (a preferred moment).
Anyway, under the preferred foliation, there is a fixed amount of time between any two moments in time, and frames which do not correspond to this preferred frame are simply not representative of the absolute ordering of events. Hence clocks are all wrong because they're all dilated, some more than others.
Quoting Metaphysician Undercover
In the spacetime model, there is no concept of 'point in time'. Time is just one of 4 dimension, all of which need to be specified to identify a point, which is called an event. There is a fixed (frame independent) separation of any two events, but that separation is called the interval, not the duration between them. Both the time and the space between any two events is frame dependent (indeterminate), but the combination of the two (the interval) is always the same.
But that's not true. Again, we can know that on the ground, clocks are going to read, say, 500 hours on the nose, while on the space station, clocks read, say, 499-point-whatever hours (I don't know what the exact difference is--I'd have to research it) relative to the 500 hours on the ground.
How is that indeterminate?
I don't see why presentism requires a preferred reference frame. When we as human beings meet together, and communicate, we call this the present. We only need to produce a reference frame if we want to measure the passing of time. Presentism doesn't necessarily require this, so it doesn't require a preferred reference frame. But when we proceed toward measuring time, time is indeterminate due to the possibilities of reference frames.
Quoting noAxioms
A "preferred foliation" might validate determinacy in time, if the preferred foliation was justified, not arbitrary. But if the preferred foliation were justified, wouldn't special relativity be contradicted?
Quoting noAxioms
Removing the possibility of a point in time is another indication that any claimed amount of time is indeterminate.
Quoting noAxioms
Right, there is a combined value of time and space. However, since what is actually measured by us, according to our capacities, is time, and space independently, and these are indeterminate, then the combined value is fundamentally indeterminate.
Quoting Terrapin Station
You seem to be forgetting that there are two definite points, between which the time is measured. One clock measures 499, the other measures 500. Therefore the amount of time between those two points is indefinite. You can say, as noAxioms does, that there is no such thing as a point in time, but that is just an admittance that any so-called amount of time is indeterminate.
?? This makes no sense to me. If the one reads 500 hours on the nose and the other reads 499 hours, 58 minutes and 30 seconds, then the amount of time between those two is not indefinite, it's a minute and 30 seconds. That's very definite.
I think you have a different concept of presentism than the one typically presented on philosophy sites, which might ask when the twins get back together and notice 10 or 20 years elapsed, isn't one of them more correct about how many years actually went by? Presentism would say yes to that, but you seem to say no, since a different amount time passed for each of them, so they're both right about it.
Quoting Metaphysician Undercover
Determinacy is unaffected by any choice of foliation. Different frames of reference do not in any way alter the causal relationship between any two events.
SR just says no preferred folation is locally detectable. It doesn't forbid its existence.
Quoting Metaphysician Undercover
You seem to use 'indeterminate' as 'not absolute'. The word means 'uncalculable', or 'unpredictable', and as Terrapin has been trying to point out, it is quite calculable. These things are just frame dependent, but completely determined given a choice of frames.
That said, time and space between any two events is indeed frame dependent, but their combination always yields the same interval. That part is thus frame independent. The interval between any two events can be given by one fixed value, and different perspectives do not change that value.
Quoting Metaphysician Undercover
This is a feature of your future light cone. That cone, not the present, delimits events which can and cannot be changed.
Similarly, the past light cone, not the present, delimits that about which we can know (events which can have an effect on us, vs those which cannot).
Neither of these fundamental things changes at the boundary of the present, except where the two cones happen to intersect the present. So no fundamental change as described here occurs at the present.
Those light cones are not frame dependent. They are 'determinate' as you put it.
Yes, that's relativity of simultaneity. The events that are simultaneous for Alice need not be simultaneous for Bob. But, again, any apparent disagreement is resolved by factoring in their respective reference frames. If they shared the same reference frame then the same events would be simultaneous for both of them.
So I don't see a conflict between presentism and realism. A problem only occurs if one assumes an absolute reference frame for determining simultaneity. (Note: one could consider a reference frame for the whole universe, but then time drops out.)
Quoting Metaphysician Undercover
No, it is determinate. This is just arithmetic (the amount of time between t1 and t2 is t2 - t1). Note that to specify times at all is to assume a particular reference frame. Normally we don't have to think about this because we (and most matter in the universe) age at about the same rate (because we move at similarly slow speeds relative to the speed of light).
There is a beginning point, and an ending point to the time period being measured. One clock measures that time period as 500 hours. Another clock measure it as 400 hours. Another, 499 hours, 58 minutes and 30 seconds, and so on. Since there is an infinity of possibilities, to the amount of time between that beginning point and the ending point, that amount of time is indeterminate.
Quoting noAxioms
Presentism assumes that only the present is real. If both the twins experienced only the present, for the entire time of separation, and continue to experience only the present, how could this be a problem to presentism? The fact that they have aged differently is irrelevant to presentism.
I don't think that presentism is capable of providing a premise for counting a quantity of time, because any past time would become unreal, therefore there can be nothing to count. So what is inconsistent to presentism, in this thought experiment, is that one twin measured 10 year and the other measured 20. Presentism really does not allow any reality to such measurements of past time.
Quoting noAxioms
I think you misunderstand SR. It strictly stipulates that no frame of reference could be preferred in the sense of being more real than another.
Quoting noAxioms
Indeterminate means without a fixed value. If the quantity of time measured between when the twins separated, to when they reunited, varies from one frame of reference to another, it is without a fixed value, and is therefore indeterminate.
Quoting noAxioms
I think you are wrong to say that the light cones are not frame dependent. Any event has a light cone. According to SR, the present of an event, or time that an event occurs, is frame dependent. Therefore the light cone for any event is frame dependent.
Quoting Andrew M
Obviously not, because Bob measures the time between t1 and t2 as 6 years, and Alice measures the time between t1 and t2 as 10 years. Therefore the quantity of time between t1 and t2 is indeterminate. So I disagree\ with you again, and I really wonder where you are getting your information from. That your statement is wrong is evident from the fact that physicists employ a "proper time". The employment of "proper time" is to create a semblance of determinacy. It's a similar principle to your "preferred foliation", it provides an illusion of determinacy.
There's not an infinity of possibilities with respect to the frames of reference in question. There are different possibilities in different frames of reference, but none of them are indeterminate.
The point is that there is a multitude of possible amounts of time between the first point and the second. Therefore the amount of time between those two points is indeterminate.
I can measure the distance between myself and that tree over there, and get an indeterminate value because one of the measuring tapes takes a path around that other tree to the left over there, and thus measures a different distance. So all measurements are indeterminate in that sense. But I could have calculated how each of those measurements would come out ahead of time. Those measurements are fixed before they are done, as opposed say to quantum measurements which are not predictable in advance.
Quoting Metaphysician Undercover
Events are fixed (by definition), not frame dependent at all. They're points in spacetime, and don't have frame dependent qualities such as velocity, duration, or length and so on. Their light cones are determined by light speed, not the frames, so those are also fixed.
t1 and t2 are 20 years and 30 years if you're using Alice's clock. Alternatively, t1 and t2 are 20 years and 26 years if you're using Bob's clock. They travel different spacetime paths which is why their ages are different.
What you can say is that the time between two points in spacetime is indeterminate.
It's not analogous unless you are claiming that the distance between yourself and the tree is indeterminate. And that's not what your claiming, because taking a side trip around another tree is not measuring the distance between yourself and the tree.
OK, I'll go with that then.
Exactly, just as the twin that takes a side trip to some other star and back is not measuring the duration between the two events of departure and return.
All things change place as time passes, it's a premise of relativity. If moving means that one cannot measure duration, then time is indefterminate.
time travel to the future is already possible and has been done in practice. The only problem is that there is no practical application that can bring you back in time. Also under the current circumstances, it takes alot of time to travel only a little in time. I don't feel like doing the exact calculations right now, but it is in order of a minute timetravel towards the future if you spend a year. In other words, with the current method, you can leave earth for a year to travel in time, and when you come back after a year for you has passed, on earth a year and one minute will have passed.
So yes it is possible, just not very practical yet.
I know of two premises of SR (one of which predates the theory by several centuries), and a third for GR. None of them are "All things change place as time passes".
It's only indeterminate if you're looking for an overaching time perspective, which is why I brought that up first.
Since there is no overarching time perspective, then it's not indeterminate. You just have to specify the reference frames. There's no reference frame-free time. The idea of that doesn't make any sense.
I think it's worse than that. Presentism cannot assume a preferred foliation of something it claims does not exist. Presentism cannot admit spacetime or foliations, and has to treat scientific theories such relativity as useful fictions.
Quoting noAxioms
Alternatively, presentism may dispense with an observer independent objective reality.
Newtonian relativity. Inertia is frame of reference dependent. There is no absolute rest.
Quoting Terrapin Station
It has nothing to do with an overarching time perspective, we went through that already. Why do you allow that idea to distract you? It's the human perspective. We designate points in time as the beginning and ending of a period of measurement. That's how we quantify time. Without such points we have no measurement of time, but the human capacity to designate such points is deficient. Therefore from the human perspective, time is indeterminate.
Indeterminate means having no fixed value. So consider this analogy. Some one asks you what time it is. By the time you say what time it is, it is no longer that time. So "what time it is" has no fixed value, and time is inherently indeterminate.
So now it's a point about, what--the notion that we can subdivide time further, or the idea that we can subdivide it into units that are quicker than we can say something?
That was an analogy, not an attempt to change the subject.
Sounds to me like you traveled about a year into the future, just like we all do. Travel into the future seems effortless. It's not doing it that's the trick.
Anyway, the subject of the thread implies that one's interpretation of time has anything to do with the possibility of time travel. Assuming time travel is to the past, as is typically assumed, it is impossible, period. A-theory has nothing to do with that.
Such a concept would involve sending information to the past, and that has never been possible under any valid interpretation of physics.
Forward is easy, at least for things with reasonably limited information. Information travels that way no problem. High speed isn't required to do it.
The question of whether closed time-like curves exist in our universe is still open, Hawking's Chronology Protection Conjecture notwhithstanding.
https://www.nature.com/articles/s41467-018-08100-1
So, physicists are really studying time-travel into the past. A-theory says they are wasting their time. They aren't.
Quoting noAxioms
You are mistaken, see the above link and references therein.
Have you worked out yet how to account for eternalism's lack of motion, or are you still ignoring that eternalism has this problem?
https://www.quantamagazine.org/a-debate-over-the-physics-of-time-20160719/
There is no "lack of motion" in eternalism, so yes I ignore fictitious problems.
Why do you think there is no motion under eternalism, particularly if that were the case, no one would advocate it?
In the article I linked to in my last post, it states that "60 physicists, along with a handful of philosophers" attended a conference to discuss this issue. Are they all incorrect?
Quoting Inis
I think that there is "no motion under eternalism" from everything I've read about it. It also states the same in the article I linked to in my previous post. Eternalism is synonymous with the block universe.
There is a lack of motion in eternalism. You would have to turn to something outside the block universe as the source of any perceived motion within the universe.
The article never says that there is no motion under anything. The word in fact never appears.
I am at the top of the stairs, and 2 seconds later, face down at the bottom. That's motion. The block has both those states, separated by 2 seconds.
It seems quite clear to me.
OK, there's a state with you at the top of the stairs, then a state with you at the bottom. Where's the motion? Aristotle demonstrated, that if you describe such changes in terms of states, you'll always need an intermediate state between the two states, to account for the change. This results in an infinite regress of always needing another state to account for the change between the two states. You falling on the stairs is the intermediary between you at the top, and you at the bottom. You falling forward is the state between you at the top, and you falling on the stairs. Ad infinitum.
Yes. That quote does not say there is no motion or no time. It just says time doesn't flow in that model.
Ditto with presentism, which also has states in between, else it is a series of discreet jumps.
Getting down to the quantum level, neither case is infinite regress. There comes a point where no measurements are taken and there are no intermediate states. This comes from me, who has thrown his lot in with the principle of locality rather than the principle of counterfactual definiteness. Can't have both....
What do you take "a static block of space-time" to mean? How is motion possible if there is no flow of time or any passage through space-time? Why does the article say that the flow of time, or passage through space-time, "must presumably be a mental construct or other illusion"?
I think I understand something about why time-travel is difficult or impossible.
Consider space-time as a 4D universe (3 dimensions of space and 1 dimension of time). In the 3D of space all objects aren't in the same state. Objects in space are in different positions and so we have more variety in space i.e. we can move in any direction in space.
The 4th dimension, time, isn't like that at all. Given a particular frame of reference, all objects in it are at the same temporal state. For example, if you and I were in the same place 2 o'clock for me is 2 o'clock for you too. There's no freedom in the 4th dimension because ALL of us are moving through it at the same pace.
I guess this is one way we can look at time travel. We have to be in different frames of reference to perceive time differently (time travel). According to Einstein's relativity if we approach the speed of light (c) then perceptible differences in time (time travel) do occur. I guess relative motion changes our frames of reference to allow time travel.
I don't know if the theory of relativity allows backwards time travel though. Forward time travel seem possible - just approach the speed of light. By extension does it mean if we slow down enough we can travel backwards in time? Unfortunately, there's no speed less than zero.
I don't think that's the case with presentism. What we notice at the present is activity, not a static state. This is what makes presentism so difficult. We notice that things are changing at the present, but logic will tell us that change requires a quantity of time. How is the present a quantity of time?
Suppose I say "now". That takes a period of time. So the present represented by that expression is a period of time. With modern technology, we reduce that period of time to the tiniest fraction of a second. nevertheless, it remains a period of time. We could say that the present is a second, a picosecond, a Planck length, and that is going toward a shorter and shorter quantity of time. We could go the other way, and say that the present is an hour, a day, a year, a million years, or billions of years. It is an arbitrary designation to stipulate that the present has a duration of X length. Nevertheless, the present always consists of a quantity of time, and therefore cannot be represented by states because things change in that quantity of time.
Quoting noAxioms
The problem, and this is what Aristotle demonstrated, is that there must be something intermediate between the two states, or else the change is not accounted for in the description, therefore the description is deficient. It doesn't matter if it's at the level of twenty seconds, or the Planck level, if the description is of two successive, and different states, there must be something intermediary to account for the "becoming" (the change from one state to the next). If your description is only in "states" then there is necessarily an infinite regress. If you posit Planck length to put an end to the infinite regress, then you still have the very same problem, but at a tiny level. You have two successive different states, with no description of how things change from one state to the next. Therefore we must posit a "becoming" which occurs between the two states. This is the argument which Aristotle used to demonstrate that "being" (as states) is fundamentally incompatible with "becoming" (change or activity). That's why he proposed a hylomorphic dualism, to account for these two distinct aspects of reality.
That would have to involve reifying time in an odd way (that's completely without justification in my view).
Quoting Inis
Yeah, they are, because the idea is incoherent. But physicists waste their time on all sorts of nonsense. Well, or it's a waste for practical purposes, at least. Sometimes these sorts of things lead to ancillary benefits.
Time travel into the past is coherent, because the past is real. Having actually occurred, events of the past have actual existence and therefore might be visited. Time travel into the future on the other hand is incoherent, because there is no time there. Time is what is measured at the present, as time passes. Therefore all time is past time. One cannot "time travel" into the future because there is no time there.
I'm puzzled why an expert general relativist like yourself wastes your time on this forum rather than publishing your views in Nature.
Because it is talking about "the flow of time, or passage through space-time," rather than motion. There is no difference in dynamics between eternalism and presentism. In fact, there is no physical difference, period. The difference is entirely metaphysical and has to do with metaphysical notions, such as the objective present, the passage of time, the existence of past and future, etc.
Nope. Presentism is falsified by several well known experiments, including time-dilation, twin paradox, and the fact that your GPS actually works.
We all have our metaphysical preferences when it comes to time (eternalism, presentism, possibilism). What we should not be doing is claiming that our preferences have been verified by the only possible interpretation of physics (either general relativity or quantum mechanics). This since there are several solutions to the equations of general relativity and several interpretations of the equations of quantum mechanics and the two sets of equations are not compatible and have not been reconciled. They both break down at the extremes.
In truth, clocks have little to do with metaphysical or philosophical notions of time and very little to do with time in physics. There is no clock which represent the "metaphysical present" or the correct "present time". Agreement about the correct time on a clock has to do only with consensus or agreement; to allow us to catch trains, planes or buses and appear at a given location to meet or decide world records in track events.. Clocks do not keep track of the "present". We synchronize our watches and divide the day up into 24hr, 60 minutes and 60 seconds only by convention not by some universal law of physics. There is in fact no universal present time. There is in fact no universal now or present; about this physics and experience can agree. All of this fails to discount the notion that the relative present at each space-time location is all there is. The past has perished and is incorporated into the present and the future is open and yet to be determined. There is no experimental evidence, empirical date or experiential phenomena which proves this to not be so.
True the universe is sometimes represented by a block universe in which time is given a physical dimension but this is merely a illustrative tool to help visualize spacetime paths not an actual representative of our "reality". Mistaking mathematical formulas and tools as anything other idealized abstract conceptualizations of "reality" is the "fallacy of misplaced concreteness". So at least a little humility is called for in assertions about the nature of time and the reality of the present versus the past and the future.
My personal convictions are that time (as commonly spoken about and conceived) is an illusion. Time does not exist independently, is not absolute, is not fixed and is really only an abstracted artificial concept based on the change, flow and flux that is the most universally observed and experienced aspect of reality. Others are welcome to their iron block frozen eternalist universe but such a conception is not confirmed by observation, experience, reason or physics.
Presentism is commonly thought to be incompatible with the relativity of simultaneity - a fundamental implication of Special Relativity. It does not depend on any particular solution or interpretation; it is not in conflict with quantum mechanics (quantum mechanics has been formulated in SR); and it is very well established experimentally.
However, whether presentism is indeed ruled out by relativity depends on exactly what claims are made in the name of presentism. Lots of arguments have been put forward for and against compatibility - go and look for them, if you are interested. (But who am I kidding...)
You seem to be interpreting presentism as a denial of relativity. But I haven't seen anyone claim that. I certainly don't.
As far as I can tell, eternalism versus presentism is just a semantic dispute. Each side accepts relativity, so accept time-dilation, the twin paradox, relativity of simultaneity, etc. The dispute just hinges on the language used to talk about it.
Consider Alice on Earth in 2019 claiming that dinosaurs exist. Is her claim true or false?
Presumably both sides will say her claim is false. Perhaps the eternalist will translate it into a tenseless claim first. Is there more to the dispute than this?
If not, then the same prospects (or lack of) for time travel are available to both presentists and eternalists.
As I mentioned earlier, you can be a presentist if you deny an objective observer-independent reality, or deny relativity.
But if you prefer an objective reality and take scientific knowledge seriously, you are confronted by situations like the following:
If you pass someone in the street, your present, among other things, includes that person. You consider that person to be real, and equally subject to the laws of physics. If this person is real, and independent of you and your present, relativity tells you that she also has her own present, which is as real to her as your present is to you. Your presents are not the same. Presentism is false.
I still don't understand. If presentism posits a passage of time while eternalism does not, then how is motion possible according to eternalism? Why is it referred to as a static block universe? What is the illusion supposed to be (in the section you quoted)?
Your present is not necessarily 'the present'. In fact, quite unlikely to be. Presentism is safe from this sort of argument in my opinion.
It doesn't matter what label you apply to any particular simultaneity hypersurface.
Or you can deny relativity, which as I mentioned earlier, is an option.
When presentists posit a passage of time, what they mean (or at least what some of them mean) is that the present time is an objective fact. Time flows by way of the present time constantly progressing forward - and that too is an objective fact of the world. This present time, which is like a moving index on every timeline, is not implied or required by any physical law. As far as physics is concerned, positing such an index is unjustified. And that is what moves (at least some) eternalists to deny the objective existence of such an index.
Quoting Luke
I think that the use of the epithet static in relation to the block universe is pointless and misleading. At best, it indicates that the block as a whole does not change - which is just a way of saying that there isn't a second time dimension, along which the block could be changing. But since no additional time dimensions were ever on the table in the presentist/eternalist debate, it is unclear why this needs to be brought up at all.
The existence of the one and only time dimension is acknowledged by both presentists and eternalists - with all that that implies: where there is time, there is motion.
Quoting SophistiCat
If the passage or flow of time has no objective existence, then I guess it must have subjective existence? It certainly appears as though time/events/things pass from the future to the past via the present moment. I take it this is the illusion? You seem to be saying that motion is separate from temporal passage, but isn't the present moment when motion occurs and events happen?
If I threw a ball in the air yesterday, and that event eternally exists according to eternalism, then is that ball still in motion (now) according to eternalism? Maybe you will say that it was only in motion yesterday when that event happened. But when do events happen according to eternalism? When are those events set in motion, so to speak? Does my ball keep getting tossed in the air repeatedly on an endless loop, or did it only happen once, or does it never actually happen? Without a present moment and passage of time in which events occur, it seems that they never can or do, according to eternalism.
Even if temporal passage is "not required by any physical law", eternalists still need to account for the appearance or illusion of passage. How can time appear to pass if no time actually passes?
I think that this statement is a little deceptive. In order for a physicist to measure time, something must be moving, changing. The physicist might take the passing of time for granted, but this does not mean that the passing of time is not required for physics, to the contrary, it is what is taken for granted. Therefore positing the passing of time by physicists, is justified, as that which is taken for granted. And, it is expressed by the second law of thermodynamics.
Quoting SophistiCat
What you refuse to acknowledge is that there is no motion in the block. Nor is motion implied. The block is a representation which effectively removes motion, that's why it's called "the block". The same principles which produce the 4D block also produce a symmetrical time dimension. This means that if it were possible that something could travel (move) through the block, the travel on the time dimension is not restricted to one direction.
The asymmetrical nature of time is represented by a principle which is distinct from the principles that produce the block. That is the second law of thermodynamics. This law describes an odd property observed in energy. The problem here is that this law is only produced from observations made by humans beings moving within "the block". We do move through the block, and the cause of this movement through the block is not accounted for by the representation, which is "the block". So the problem is that the 4D representation provides no premise whereby a human being could move through the block yet we do move through the block.
Therefore we must be forced to move, as time passes, by a power which is not represented by "the block". The force which powers human beings through the block (the passing of time) is not represented in "the block". However, the consequence of this force which powers us through the block, is our observations of the block as we and everything else observable, are being powered through it; and this is what give us that second law of thermodynamics. The second law describes what we observe as the effects of ourselves, and everything else, being forced through the block by a cause which is not represented as part of "the block". It is the description of our motion through the block (which is caused by something not represented by "the block") which validates the asymmetrical time as opposed to the symmetrical time of "the block".
Quoting Luke
The argument you are making seems to follow this rationale:
Premise 1. I experience a changing state of affairs.
Premise 2. If I experience a changing state of affairs, then becoming is a real feature of the reality.
Premise 3: If becoming is a real feature of reality, then eternalism is false.
Conclusion: Therefore eternalism is false.
The eternalist will counter this experience based argument for the A theory of time with an analogy with space. You are only ever aware of one location in space and that is the one you experience, which we tend to call "right here." You experience your location in space, but you do not experience any other location in space or all locations of space. However, simply because you experience your location of space that does not mean that that location of space is the only location of space that exists. Indeed, I may never go to China or to Pluto or outside the milky way galaxy, but I don't assume that those locations are simply mental fictions. If someone asked, "if other locations in space exist, then why don't I experience them" it would be best to respond with "why would one assume that X exists only if one experiences X?"
Similarly, the eternalist will argue that experiences do not necessarily reveal the metaphysical reality of said experiences. When we say we experience the flow of time, it flows within the block universe; however, outside the block universe there is no flow of time. Consider the phrase "moving picture," when looking at old film rolls, from outside the film role, they seem static and unmoving and unchanging, but inside the film roll is the unstatic and changing movie.
Here is a link for more:
http://news.mit.edu/2015/book-brad-skow-does-time-pass-0128
http://web.mit.edu/bskow/www/research/experience.pdf
https://sci-hub.tw/https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1468-0068.2010.00784.x
I freely admit, I do not have the time or the expertise to fully evaluate the arguments for and against presentism and its various forms. It is just I am aware of these arguments and the issue seems far from absolutely settled.
There are versions of relativized presentism, cone presentism and point presentism. There are those who questions the metaphysical assumptions of the STR but not its empirical consequences. There are versions of Quantum Gravity (held to be a more fundamental physical theory than STR) with fixed foliations which allow for presentism. There are very reputable physicists and cosmologist who argue against a block universe and for forms of presentism. There is the expanding block universe models which although they preserve the reality of the past allow for an open or crystallizing future.
My point is not that I am correct and everyone else is wrong, my point is we do not know for certain and so absolute dogmatism and brusque dismissal of other points of view is unwarranted.
I am aware that the standard interpretation of STR and particularly the notion of "simultaneous events" leads to problems for standard naïve versions of presentism.
I fully understand Feynmans point in his lecture about what is "now
"What we mean by “right now” is a mysterious thing which we cannot define and we cannot affect, but it can affect us later, or we could have affected it if we had done something far enough in the past. When we look at the star Alpha Centauri, we see it as it was four years ago: we might wonder what it is like “now”. “Now” means at the same time from our special coordinate system. We can only see Alpha Centauri by the light that has come from our past, up to four years age, but we do not know what it is doing “now”: it will take four years before what it is doing “now” can affect us. Alpha Centauri “now” is an idea or concept of our mind; it is not something that is really definable physically at the moment, because we have to wait to observe it; we cannot even define it right “now”. The “now” depends on the coordinate system. If, for example, Alpha Centauri were moving, an observer there would not agree with us because he would put his axis at an angle and his “now” would be a different time. We have already talked about the fact that simultaneity is not a unique thing.……………….. There is no one who can tell us what is really happening right now, at any reasonable distance, because that is unobservable.
There is no view from everywhere; there is no view from nowhere; all views are localized and limited.
The eternalist view (B theory, block, static, iron universe, 4D representation of time as a physical dimension) would seem to imply that dinosaurs still exist (are actual) at their location within the spacetime block and that the results of the 2020 U.S. Presidential Election already exist at their location in the future and these are interpretations which I just do not believe can be true; our current interpretations and theories not withstanding, so I look to the alternatives present within reason and science..
There is also a lot of misunderstanding about clocks, proper time, correct time, time dilation and other forms of nonsense in the thread but I do not participate to endlessly banter, mostly looking at threads just inspires me to research the subject elsewhere, to play with ideas.
We directly perceive motion with our senses in our subjective present (obviously), but we conceptualize motion as change over time, which can happen in the past or in the future, here or there, perceived or unnoticed. This concept of motion is available to both presentists and eternalists, but presentists will additionally qualify it with an objective temporal modality.
Quoting Luke
Yeah, this is where I definitely part company with both parties. Not that I think that either of them is wrong - I just think that this talk of existence is both confusing and pointless. I'll leave it to advocates to untangle this mess.
You say that the concept of motion is available to eternalists, but it seems logically incoherent to me. You claim that motion or change can(?) happen in the past or in the future, but it fails to explain when anything actually happens in the block universe. Future events already exist, so have they already happened? Also, I still have no idea how you account for the illusion mentioned in the article.
Quoting SophistiCat
I'm not sure what you were previously defending then, if not eternalism. But I understand if you don't wish to continue.
Yes. The way I would state it is that our knowledge (of reality) is reference-frame dependent. In my reference frame, I make a distinction between the past, present and future. Per that distinction, other people and many other things exist, but dinosaurs do not exist. Similarly, while each person has their own reference frame (and thus present), dinosaurs do not exist for them either.
So I think on that view, presentism, relativity and realism are compatible.
I want to know the status of "dinosaurs"? Are they truly extinct and vanished from the universe (except for their bones and descendants)?
Or are they still moving and inhabiting the earth in their region of the 4D space time block and the only reason we can't get back there is because our timeline won't curve enough to take us back?
I don't believe that I've made any argument from experience. I have only been trying to point out to those who are quick to dismiss presentism, that eternalism has problems of its own.
Quoting Walter Pound
I wouldn't argue only from my own experience; it seems that we're all in this together at present (or, at least, you and I are). More than just my personal experience; physical aging, our use of calendars, many of our scientific theories, and the one-way arrow of time all support the "argument" (or require the fact) that time actually passes or that we pass through time.
Quoting Walter Pound
I find it odd that you attached articles by someone who does not support this spatial analogy (see the author's example of the red and green rooms in the 'experience.pdf' article you posted). The author of those articles advocates the moving spotlight theory, which is a mixed view of eternalism and presentism. Furthermore, the analogy is quite weak. Unlike my freedom of movement in space, I am not free to travel to the past, and I am extremely limited in my "choice" of future time travel destinations.
But neither am I arguing only in favour of presentism, so this is neither here nor there (so to speak). Nevertheless, I enjoyed the articles which again note that illusion of passage is an intrinsic feature of the B-theory, so thanks for posting them.
Except you have just argued for observer dependence.
I have no idea why you think our knowledge is reference-frame dependent. We all know relativity, and it has nothing to do with which particular reference frame we happen to be in.
[
Dinosaur world-lines exist in the distant past.
No. Dinosaurs existed in the distant past independent of any observers. Whereas our knowledge of dinosaurs depends on observation.
Quoting Inis
We know relativity as a consequence of theorizing about what is observed (in our reference frame).
You think you can observe your present?
I think I can observe things in the present.
Well you can't. Everything in your present is space-like separated from you.
Thats already inherent in the notion of "observation" isn't it? Or are you arguing that gaining any information is impossible?
Frankly have no clue what you mean. Nevertheless, permit me to reiterate:
Your present hypersurface is inaccessible to you. If you seek information about any of the simultaneous events that make up your present, you have to wait for the information to become part of your past light-cone.
I think they might be suggesting that the present moment is when observations are made. Why do we need to define it as time of observation minus information processing time instead?
But I still observe the objects in my present. Either we are referring to an objective present, in which case all information I currently observe refers to an objective past, or we are referring to my subjective present, in which case I can observe objects in my present.
I now observe the moon as it was a second ago and everything on my desk even sooner. The timing can be factored in as needed.
The point is that relativity is a theory that explains what human beings observe and measure in a specific frame of reference.
Under presentism, there is no hypersurface or light cone, both 4 dimensional concepts. So if you seek information about any of the simultaneous events that make up your present, you have to wait for the information to come to you, at which time the information is no longer about the present.
Same thing, but my attempt to word it the presentist way. Walter Pound (the rarely seen OP) put it quite well in his post on the prior page.
Quoting Echarmion
The observing is done in your present, but what is observed is only right here, nowhere else. I cannot see the present moon, but I see light in the image of moon right now. That light is right here, and from that image, I deduce a moon in the past and infer the moon still being there in the present, totally unmeasured. This process is automatic and not usually noticed. Andrew M points this out.
What you refer to is probably a proposed objective present. In that scenario, present reality is observer independent, and the present defines you, not the other way around. That present is not reference frame dependent, and thus reality is the same for everybody (as it should be for any observer-independent stance).
It is almost self contradictory since nothing you see is real. The moon you see cannot be real because you see a past version of it that cannot exist. I don't find that contradictory. You just cannot see anything real, but it is an observer-independent view, so it still exists just fine.
In an observer-defined reality, each observer observes a different point in the universe, and observes only that point, with other objects existing relative to that observation, and each observer defines a different reality, which can be a local state (presentism), or a light cone (eternalism) .
I am sort of in this observer-defined camp myself. I have a relational view of existence, sort of like idealism except it has nothing to do with people or consciousness, and things cause themselves to be real to me, or to the rock over there, whereas under idealism, my conscious observation I think causes those things to be real.
I wouldn't say that this is "right now", because the image is created, and that takes time. The light hitting your eyes is processed, and the image is created. So even the light from the moon hitting your eyes is in the past by the time you see the image.
Quite true, but it is still at least 'right here', or at least as much as 'here' can be defined for an entity which doesn't exist all in one place.
What do you think it means for an entity not to exist all at one place? Could one part of that entity be in one frame of reference, and another part be in another?
All (reasonably local, like not outside the Hubble Sphere) parts exist in all frames.
Being not all in one place means I am not in a defined state except to an event which has measured that entire state, which can only be in the future of the state being defined.
Why would this event, which measures all the defined states as one state, need to be in the future of those states? Can't the different defined states just be compared as occurring in different frames of reference?
Measurement doesn't require processing. The light hits me somewhere (eyes, toenail, whatever) and I've measured the moon. It exists to me now. The processing is only necessary for me to know it exists, but knowing doesn't define existence except under idealism where the photon never hit me at all.
It takes time to gather all information about the spread-out state into one point (said future event) which can be anywhere, not necessarily an event that is part of me.
Choosing different frames of reference just defines a different set of events to be 'my state'. Under presentism, there is only the preferred frame, and other frames don't represent my actual state.
Of course measurement requires processing, it is a process. You cannot measure something without actually measuring it. That's the measurement problem which SR claims to resolve, the problem that we cannot get to the another pov to measure what happens from that pov. The fastest relation between one point of view and another is the speed of light, so light speed becomes the standard for comparing one pov to another. But even to measure something using light takes time, and the thing might be moving in that time which it takes to measure it.
Quoting noAxioms
Measuring creates a knowing. If there is no knowing, then there has been no measuring.
Quoting noAxioms
Wouldn't you agree that the movements of my arms and legs ought to be understood as occurring in a different frame of reference from the movements occurring within the neurology of my brain, and my nervous system?
We have different definitions of measurement. I'm speaking of measurement in the QM wave-function collapse sort of way. That interaction is 'actually measuring it'.
Yes, I figured that was the definition under which you were working. I'm not talking about knowing.
I don't see how any of that doesn't occur in all frames of reference. Maybe I don't understand how you're using the term. I'm interpreting it as 'inertial frame of reference' but maybe you mean POV or something, except no POV is specified then.
Sure, but not every interaction is an act of measuring. An act of measuring is a particular type of act. So it makes no sense to say that light hitting your toe, or hitting your eye is an act of measuring that light. This would be like saying that light hitting a rock is an act of measurement. In QM experiments, the interaction is with a special type of equipment, a measuring device, it is not a case of light hitting a rock, and the rock measuring that light.
I had mentioned the rock above. Yes, it very much is a measurement. Thing X (source of photon) has now caused an effect on said rock, and X now exists to the rock. That's how QM measurements work. It causes the state of X and the state of the rock to become entangled. The special equipment in labs is only special because it records the measurement precisely for the purpose of the knowledge of the lab guys, but measurement itself is trivial.
You can assert otherwise, but then we're just talking about different things. You asked me what it means for an extended object (not all in one point in space) to not be in a defined state at the present, and this is what I mean by that.
Under presentism, there has to be a present hypersurface, and there has to be only one of them. Unless you pull the trick of denying objective reality etc.
The hypersurface will be 3D, and defined by all simultaneous events - i.e. by everything in reality. The light-cone will be a convenient mathematical tool for figuring out how long ago events happened, and why different observers disagree about such things.
It seems like you do not know what measurement is. Measurement, by definition requires a comparison. The measurement devices in QM are calibrated to perform comparisons.
Quoting noAxioms
Yes, we're talking about different things. You've created a fictitious definition of "measurement", and now you've drifted off into your imaginary realm where rocks and toes are performing measurements of light energy. So I see your explanation of what I asked is completely irrelevant and imaginary. It's nonsense.
So when I open the box to check if the cat is dead or alive, what carefully calibrated device to I need to do this? It can be done in the total darkness if that helps.
The rock is doing a comparison of photon detected vs photon not detected. The state of the rock is different depending on this comparison.
And that just seems to be a deliberate dodge of the question. The eternalist stance (as I understand it is the past, the present and the future all have equal ontologic status. They all exist and are real in the same manner.
The problem is virtually no one actually believes that. It arises from treating time as just another physical dimension and then drawing block diagrams to illustrate ones passage through the time block. Which is a useful tool (just like train routes on a map) but no more represents the actual passage than the line a train will take drawn on a map is of the actual train ride.. One can not empirically directly demonstrate the continuing reality of the past. It is all a fallacy of misplaced concreteness mistaking a mathematical formula (always an abstraction and idealization and which fails at the extremes) for reality itself. One cannot derive the concrete from the abstract in its full measure.
Your question is answered.
Quoting prothero
But not at the same time, or the same place..
Quoting prothero
If you've studied relativity (and quantum mechanics) eternalism is inevitable. Many physicists don't like that for religious reasons, which is why they try to invent new physics.
Quoting prothero
How do you empirically directly demonstrate the momentary reality of the present?
How about we say that things interact with each other, but interacting things do not necessarily measure each other. Otherwise we'd have no difference between interacting with something and measuring something. Measuring is a special activity of comparison which human beings with minds do. Things which interact with each other are not necessarily gather information into one point. Do you know what it means to gather information? Or are you just making up a nonsense definition of that, to go along with your nonsense definition of measurement?
Quoting noAxioms
So the rock compares it's own state prior to its interaction with the photon to its own state posterior to its interaction with the photon? That requires a memory. The day you find a rock capable of doing that comparison, let me know.
I don't understand your question. Again, motion is change (specifically, of position, or more generally, of any property) over time. How is this a problem for eternalism? There are timelines, and there are properties that change along those timelines. What, specifically, is incoherent in this picture?
Quoting Luke
You are just needlessly confusing yourself with this existence business. Like I said, I don't see much use for it, but if you insist on talking about it, just think logically. Every event in a block universe has a spacial and a temporal coordinate: (x, t). So if you ask when an event exists, the only sensible answer is the obvious one: it exists at t. Just as if you ask where it exists, the answer would be x.
Interaction implies two way relationship, so perhaps a 1-way interaction.
The moon is a poor example since we're in the gravitational field of the moon at all times and it is impossible for it not to be there, even if hidden behind a curtain. A specific state can be collapsed to us only after at least a second, but the moon in general cannot cease existence just by no longer looking at it, so to speak.
You're describing a different dictionary definition of the word. A QM measurement is nothing of the sort, unless you ascribe to the Wigner interpretation I guess. I'd rather not limit myself to such a solipsistic interpretation of QM. Even Wigner himself bailed on support of his own interpretation for that reason.
I don't think I used the term 'gather information' so far.
You make comparison sound like a decision. I'm just saying that the rock is in a different state with the photon than it would be without (or with a different) photon. It doesn't make a comparison between those two states. Nothing can since any system has access to only one of the two states.
Rocks have great memory. Ask the geologists. But that is on a classic scale. From a QM standpoint, all matter has perfect memory, hence physics' conservation of information principle. There, now I've used the term 'information', but the physics definition, not the one you're using.
Anyway, I think we cannot communicate on this subject. You insist on the everyday language meaning of my words and not the physics ones.
And if the presentist also denies the second law of thermodynamics as constituting a direction or orientation of the present, then time-travel into the past or future could be seen as being nonsensical in virtue of experience not being linearly ordered.
I can't see how a 1-way interaction could be possible. How could one thing have an effect on another, without itself being affected? But a two way relationship does not imply measurement.
Quoting noAxioms
A QM measurement is clearly a comparison. I don't know how you can think that it's not. There's an experiment and the results are compared to standards, mathematics is applied, to produce a conclusion which constitutes the measurement. The equipment is like any other measurement tool, it doesn't just sit there and give a measurement. Whatever it gives must be interpreted according to a standard (compared), in order that there has been a measurement. Consider a thermometer. It sits there and produces a reading, a number. But that number is meaningless, it's not a measurement until it's put into the context of a scale, K, C, or F. Then, in comparison to this scale, the number recorded has meaning as a measurement.
An interaction not only needs to be recorded (remembered), but it also needs to be compared to a scale in order that it be measured.
Quoting noAxioms
It is a decision, that's what measurement is, it's a matter of deciding which things to compare to which scales, to get a valid measurement. You wouldn't compare a thermometer reading to a colour chart, to see if 30 degrees is green or red, rather, you'd compare it to a temperature chart to see if it's warm or cold..
Quoting noAxioms
I actually know quite a few geologists and none of them talk about rocks having memory.
Quoting noAxioms
I think that the real problem here is that you make up nonsense meanings for words and then you pretend that these are the meanings which the words have in physics. I happen to know some physicists too.
Which question?
Quoting SophistiCat
Motion is a problem for eternalism because temporal passage is an illusion according to eternalism. Without passage through time, there can be no motion. How do we get from one time to the next?
Quoting SophistiCat
It seems odd to call it "change" when nothing actually changes. Everything just exists. There is nothing to transport us from one time to another. Temporal passage is an illusion. There is no motion.
Quoting SophistiCat
The disagreement between us seems to be that you (and some others) are speaking from a physics point of view, whereas I am speaking from a philosophy of time point of view. In philosophy of time, eternalism is an ontological theory (about existence) which says that all times equally exist and objective temporal passage is an illusion.
I have been trying to convince you that motion is not possible for eternalism purely as a logical consequence of the principles of eternalism, but since that doesn't seem to be working, take a look at the online article I posted, or the articles that recently posted. I thought we would be discussing things in terms of philosophy of time since this is a philosophy forum.
Quoting SophistiCat
I never asked you when or where an event exists; I asked you to explain how anything can happen in a block universe, in which temporal passage is an illusion and everything already exists at all times. Perhaps you could finally address my questions regarding this illusion.
Simply false. Eternalists have clocks.
Quoting Luke
Eternalists have clocks and change happens.
Quoting Luke
Eternalism doesn't claim that, though. The fact that all times are equally real does not preclude passage from one time to another.
So what? Eternalists claim that temporal passage is an illusion.
Quoting Inis
Prove it. I'll go first:
Quoting Wikipedia
No they don't.
Quoting Luke
You are conflating "passage of time" (which is measured by clocks) with the wikipedia expression "objective flow of time" (which doesn't exist).
There is no flow of time. This has been dealt with in this or recent similar threads. It is an incoherent misconception that does not bear scrutiny. It doesn't even work under presentism. What is this flow supposed to be relative to?
No one, other than you, thinks that the static block universe precludes clocks, motion, change. Given that time is one of the dimensions of the block, to claim that time doesn't exist in the block, seems somewhat absurd. If someone were to claim that one of the spatial dimensions did not exist, that it was an illusion, you would think they were joking. You're not joking are you?
I don't buy your distinction. What is the passage of time supposed to be relative to? And where is your proof?
Quoting Inis
I never said there was no time, but eternalism says there is no passage.
There you go again. Time is a dimension of the block universe. Clocks measure the passage of time, in their reference frame.
You claimed that there is an objective flow of time. What is this flow relative to?
Quoting Luke
Tediously false.
Why couldn't the same be said about the flow of time? What makes that an "incoherent misconception"?
Quoting Inis
I never made this positive claim. The Wikipedia article states that there is no objective flow of time according to eternalism. I take "objective" here to refer to mind independence, not frame independence; that is, as opposed to "subjective".
More proof of my characterisation of eternalism can be found in the article that Walter Pound attached to his post earlier:
Quoting Experience and the Passage of Time - Bradford Skow
The B-theory is often synonymous with eternalism, which is how I have been using it throughout this discussion. According to Skow's article, "B-theorists [or eternalists] deny that the passage of time is a real phenomenon".
What does time flow relative to?
How fast does it flow relative to this thing?
If it changed speed, or even stopped flowing altogether, would you notice?
Why don't we experience the flow?
How long does the present last for?
ETA: You appear to have overlooked the final sentence of the Wikipedia quote I posted:
I have to agree with Luke on this one. 'Passage of time' implies flow to the average person, and I don't think the typical eternalist would ever use that term. I wouldn't. Clocks measure duration (length in the temporal dimension), and you seem to equate 'passage' with that, but I don't, and neither does most of the literature, as Luke has been pointing out.
Past events occurred. They're no longer occurring. Time is simply change or motion. It's not something you can "travel in." It rather is the traveling so to speak.
OK, so if time is simply change, why can't we change what has already occurred then? There must be more to time than simple change, or else we could change what has already occurred.
You mean change something that changed so that it doesn't change that way? How would the idea of that even make sense? It would be an identity violation for one. Remember that time only is those changes. It's not something aside from them.
Once something changes all you can do is change it some other way. You can't "travel in change," the idea of that is just nonsensical .
That change is an identity violation is tautological.
You said time is change. There must be something which changes or else there could be no change. The only thing that could change is something which already is, and this is events which have occurred in the past. If it's an identity violation to change something which has already changed, then time is an identity violation. Where's the problem?
Quoting Terrapin Station
How is the idea of traveling in change nonsensical? Change is all around us, We exist in change. I travel in change everyday. Sometimes I even pay for my travel with change. With free will, why can't we change the change? Or are you determinist?
I didn't say that change is an identity violation. I said that the idea that we could "take back" something that changed is. Look at what I wrote again: "You mean change something that changed so that it doesn't change that way?" That's what would be an identity violation. Change isn't.
Quoting Metaphysician Undercover
(1) Relations and (2) things could appear or disappear.
Quoting Metaphysician Undercover
By not making the slightest bit of sense. You'd have to explain what it would be to "travel in change." Changing isn't the same thing as "traveling in change." Change isn't a place that you can move around in. Change is a process. "Traveling in change" would mean that change is some sort of "thing" that we can move around in . . . which is a difficult idea to even clearly express in words, because it's just completely nonsensical.
A, B and C change to D, E and F.
You want to propose somehow "traveling back to that change," to experience it again, or to change it some other way, or whatever.
How exactly would it make sense to "travel back to that (particular) change"?
Let's say that all that you really mean is changing D, E, and F back to A, B and C, and then A, B and C change to G, H and I instead. Well, that's just two additional changes. It doesn't somehow erase the initial change. That's was the case regardless. It happened, It can't unhappen.. We just had further changes.
So you'd have to explain how it would make sense to "travel back in change."
How is this different from any type of change? All change is a matter of taking back something that already is. that's just what change is, and it is by definition an identity violation.
You seem to be suggesting that some things have special status. Some things we can change, but others we cannot. What validates that special status of being unchangeable?
Quoting Terrapin Station
I don't see how this is any different from any standard matter of "possibility". The way that something has already changed is only one of the many possible ways in which it could have changed. Why not choose a different way, and make the thing change in that way instead? You simply negate one possibility in preference of another. It doesn't violate identity any more than any case of choosing one possibility over another. The act of changing what has already changed violates its identity, but that's what change does, ipso facto.
Quoting Terrapin Station
Obviously you've got everything backward here, and it's you whose not making sense. We travel in space, and space is not a thing. So your claim that there must be some sort of "thing" for us to travel in, is the opposite of what is the case. "Things" just hinder travel, as being in the way. So if change is a process, and this is a lack of "things", I think it would be the most conducive for efficient travel.
Quoting Terrapin Station
Your premise is that time is simply change. If this is the case, then there is no difference between changes which have not yet occurred, and changes which have already occurred. We can consider each, future change and past change, as a possibility of change, and act accordingly, whether we like or dislike those possible changes.
Quoting Terrapin Station
In the very same way that it makes sense to travel toward a possible change in the future, it also makes sense to travel toward a possible change in the past, if time is simply change, which is your premise.
Quoting Terrapin Station
I don't know what you mean here. If G, H, and I are chosen instead of D, E, and F, then D, E, and F, are possibilities which are not actualized. It's not a matter of erasing these possibilities, it's a matter of choosing other possibilities instead.
Let's say that A is five feet to the right (from perspective x) of B.
They move relative to each other, so that A is now six feet to the right of B.
Now, no matter what we do, A was five feet to the right of B . We can't change that fact. We also can't change the fact that A is now six feet to the right of B. And once more changes happen, we can't change the fact that A was six feet to the right of B.
What you tried to propose was via later changes, that we can somehow "travel" to A being five feet to the right of B and change things so that A, say, stays five feet to the right of B, and never moves six feet to the right of B. That's an identity violation in the sense that you're trying to "erase" the fact that A was six feet to the right of B.
And you'd need to explain how you could travel in change . . . which maybe you tried to do later in the post, but I didn't and won't read past what I quoted.
One thing at a time if you don't want stuff you type to be ignored.
Your premise is that time is change. So "was" in the sense of "past time" is meaningless by that premise. You have nothing to differentiate past change from future change. All we have is either A is five feet to the right of B, or A is not five feet to the right of B. And either of these can be changed through time, which is change.
If you want to introduce a premise which states that something which has occurred in the past cannot be changed, then you need to allow that time is more than just change. You need a premise which gives past changes special status over future changes, as being unchangeable.
I don't think you need a notion of "past change" in order to hold that when you change 1)A to B, 2)B to A and then 3) A to B again 1) is not identical to 3), unless the state you change is the state of the entire universe. Because under that condition, 1) happens in a different universe from 3), and so the full descriptions of the states would not be identical. If you did change the entire state of the universe, then you would time travel, but since this presumably includes your internal state, you wouldn't notice.
That comment simply makes no sense. I'm not saying anything like "There is no time." I'm in no way eliminating time. There is time. I'm simply saying what time is ontologically. Time is change. Past time is changes that have happened.
You completely ignored the entire content of the post explaining the issues by the way.
Even changing the entire universe wouldn't do it (especially if one is a nominalist). It's still two different instantiations of the "same thing" (in quotation marks because it's not literally the same thing).
Would your premise be something like "If time isn't different than change/motion, then there would be no difference between motion/changes that are occurring, motion/changes that occurred, and motion/changes that have yet to occur"?
If that's your premise, you'd have to explain how you arrived at it, as it makes no sense to me.
1) and 3) are identical unless "A changes to B" does not mean the same thing as "A changes to B". But that would be nonsense if it didn't.
Quoting Echarmion
I don't see where you get the premise that it would be a different universe. Anyway, "A changes to B" means the same thing as "A changes to B", and whatever universe your referring to is irrelevant unless you allow for violation of the law of identity..
Quoting Terrapin Station
I read your post, but it's not relevant to your premise that time is change, which is what I am interested in. So if time is change, and past time is changes that have happened, then how do we differentiate between changes which have already happened and changes which have not yet happened? You can't refer to time to make that differentiation, because time is simply change.
Quoting Terrapin Station
I thought that it was obvious. Time is change, and nothing else. By what principle then would you differentiate between past changes, present changes and future changes. You cannot refer to time to differentiate these categories of change because time is change. That would be like differentiating the categories of change by referring to change. We can't do that we need a means for defining different types of change, past, present, and future. If time defines the types of change, then it is not simply change, but a defining aspect of change.
To differentiate categories of change (past, present and future), by referring to time, time must be something other than change. For example, to differentiate categories of objects according to size, size must be something other than an object.
Admittedly, my wording was imprecise at best. What I mean is this: Events in the universe are connected, the way we perceive this connection is as cause and effect. Any change that happens will propagate through the entire universe eventually. You can never have the same change again because the first change is already up and gone, having changed the universe. In order to do the exact same thing again, you'd need to recreate the exact universe that change happened in. But even if this were possible, it would preclude the notion of time "travel" because you'd have to somehow get out of the universe before it was recreated.
No two instances of something are actually identical. (I'm a nominalist.)
Quoting Metaphysician Undercover
You just said the difference. Changes that happened are different than changes that haven't happened. One thing happened. One has not. (And a third option is that it's a change that's happening.)
For example, think of your phenomenal experience. You watch a bird fly from one tree to another. As you're watching it, it's happening. Then you have a memory of it (which is another change after (watching) the bird flying from one tree to another). The change happened but is not happening. Maybe you'll experience the bird flying back to the first tree after that, but it hasn't happened yet.
That's the difference.
It's a brute fact of changes that they aren't all simultaneous. In terms of experience, you don't experience them all together. Just like it would be a brute fact about changes if they were all simultaneous, or you could experience them all together. Of course, the mere fact that there are changes at all means that change is not something that can be simultaneous--the idea of that is incoherent. It wouldn't be change if one thing didn't happen after another. For change to be change, one thing has to happen after another. That's what time is. Hence, time is change.
The only changes that exist, by the way, are the changes that are happening. Changes that happened existed, but no longer do. Changes that haven't happened do not yet exist, but they will.
And size is not something different than an object, either.
OK, then I agree, if A changes to B, that is a uniquely particular event which cannot be exactly replicated.
Quoting Terrapin Station
I agree, identical ought to mean one and the same. If they are two, then they are not identical. This is expressed by Leibniz as the identity of indiscernibles.
Quoting Terrapin Station
OK, but if there is a difference between changes which have happened and changes which have not yet happened, then this is a temporal difference. Therefore time is something other than change. Or, is it your claim that the difference between future and past is not temporal?
Quoting Terrapin Station
What? "Size" has the same meaning as "object"?
You don't think that I'm denying temporal differences, do you?
To tell you the truth, I don't know what you're denying. You have claimed time is change, and that's nonsense to me, so I'm trying to figure out exactly what you mean by this.
Time has different aspects, change is one, the difference between future and past is another. The two are not the same.
I'm not denying temporal differences, so pointing out that I'm specifying temporal differences isn't an argument against what I'm saying, it's a feature of what I'm saying. Yes, those are temporal differences. That's the whole point.
Let's try it this way: could you have a change or motion if one "thing" didn't happen after another "thing"?
"Time is change" is incompatible with "the difference between future and past is temporal", because this difference which is an aspect of time, is not itself a change. Future never changes into past. So, yes it is an argument against what you've said.
Quoting Terrapin Station
I agree that change requires time, but this does not imply that time is change. To support your claim that time is change, I think you need to demonstrate that change is required for time. So let's try it this way. Could time pass without any change occurring?
No, of course not. And obviously I'd say that if I'm saying that time and change are identical.
Re "this difference which is an aspect of time, is not itself a change." It's a difference that's an aspect of change, because time and change are identical.
"Future never changes into past."
Of course. "Changes that haven't happened yet change into changes that already happened" is incoherent, isn't it?
OK, that's you're assertion. Can you justify it? I see no problem conceiving of time passing without any change. Imagine a very short period of time, Planck length or shorter. Physicists have determined that no physical change can occur in a shorter period of time. However, that short period of time must pass, and this time must pass without any physical change, according to what the physicists have determined. Therefore time passes without any change. To justify your assertion you need to demonstrate that this conception is impossible.
Quoting Terrapin Station
Right, the difference between "changes that haven't happened yet" (future) and "changes that already happened" (past), is something other than a change. Therefore time is other than change.
According to what specifically?
"The Planck time is by many physicists considered to be the shortest possible measurable time interval; however, this is still a matter of debate."
You just said that according to what physicists have determined, time shorter than Planck time must pass without any changes. You wrote "this time must pass without any physical change, according to what the physicists have determined"
I'm asking you for the support for that claim. How have physicists determined this?
I said:
"Physicists have determined that no physical change can occur in a shorter period of time."
My conclusion is that in a shorter period of time change does not occur.
You wrote "this time must pass without any physical change, according to what the physicists have determined"
I'm asking you about that.
Physicists have determined that physical change occurs in quantum units. I can conceive of a period of time shorter than the amount of time required for a quanta of physical change. This short period of time must pass without any physical change.
So when you say that something has been determined you mean that you and others can conceive of it?
What I'm asking you about is your claim about physicsts determining something. Do you understand that?
I explained what I meant. Now you're just changing the subject because you have no defense for your assertion.
It's not changing the subject. You made a claim about physicists determining something, and that claim was part of an argument against my view.. Okay, so all you meant by "physicists have determined" is that you can conceive of something, is that right? I just want to confirm that first.
I am sorry for any ambiguity, it was unintentional.
Can we proceed to the justification of your assertion, that time is change?
I want to address your comments first. That's part of justifying this against alternate views.
Okay, so in your conception, does time passing without physical change amount to time passing via nonphysical change, or just no change at all?
I don't know what you would mean by "nonphysical change". You'd have to explain how such a thing could be possible.
Sorry to jump in on this discussion, but you contradict yourself. Physicists have determined no such thing, especially since this would violate conservation laws.
Quoting Metaphysician Undercover
You quote the definition, which is about measurable interval, and yet above you claim that no change takes place in that interval. It simply does not follow that something doesn't exist (small change) just because it cannot be measured.
I don't know what nonphysical anything would be. But who knows what you'd claim, and you specified physical change, as if there might be some other sort of change.
Okay, so you're using the word "pass" to refer to an absence of change? Could you explain that sense of "pass," as I'm unfamiliar with it.
I think that you cannot truthfully state that a change has taken place unless that change has been measured. To judge that a change has occurred is to have performed some kind of measurement. To say that a change has occurred, but it cannot be measured is contradictory, because to determine change is to make some sort of measurement.
Quoting Terrapin Station
That's the point, you're the one arguing time is change. Why would I accept time is a non-physical change as justification of your claim? You would need to explain what you mean by that.
Quoting Terrapin Station
No, "pass" is not necessarily an absence of change, it can occur, as in the case of time, with an absence of change. I mean it in the sense of to proceed. Time may proceed without physical change.
If you insist that this procedure is some sort of change, then we'd have to consider the possibility of non-physical change. But that would require some explaining.
Another fallacious mistake. I said you cannot assert that a change has not taken place just because it cannot be measured. But you are asserting exactly that.
I'm not positing nonphysical change. I'd say the idea of nonphysical anything is incoherent. I'm a physicalist and a nominalist who rejects that there are any real abstracts.
I have the same problem with "proceed." You'd have to explain how we could have something proceed without changing.
I was not asserting that. I've been saying that time is not change. It's Terrapin's assumption, that time is change, which leads to the conclusion that change which cannot be measured has occurred.
Quoting Terrapin Station
As per my explanation, time may pass, or "proceeds" without any physical change. That was my explanation. Don't create the illusion of circular reasoning by asking me to repeat the explanation I've already made. Remember when I made the explanation, you had difficulty distinguishing between the part of the explanation which I said physicists had demonstrated and the part which was my conception.
You just won't accept my explanation because you refuse to consider the possibility of proceeding without change, even though I explained it as time passing without change. If this is too difficult for you, then let's consider the possibility of non-physical change. Then we might create compatibility between you assertion "time is change", and my description of something (time) proceeding without any physical change. What do you think, will this make "non-physical change" coherent, if we say that time is change, yet we allow that time can pass without physical change occurring?
To say "phenomena is always changing" is to assume the meaning of "phenomena could be still". But what exactly is a still experience? For i've never had an intrinsically still experience. Whenever I have ordinarily declared that everything is still, is in relation to performing a task during which I observed things were changing, but not in a way considered important to the task.
So if 'still phenomena' is logically impossible, then to assert the opposite that phenomena is changing is meaningless if interpreted to be an essential statement of experience.
Right. That's what you said. The problem is that "pass" and "proceed" are terms that imply change or motion, unless you have some novel definition of them that you'd need to explain for the idea of time not requiring change or motion to make any sense.
I didn't actually specify "physical change" in anything I said, by the way. Just change. So if you want to posit "nonphysical change"--whatever that would be--okay, but it's still change.
One of those "you can't have x if there is none of x's opposite" arguments?
Fair enough. You said physicists have determined that, and they don't claim that.
With that I agree. "I changed my political viewpoint after the last election" "How much?" "By just over 2 hours"
Indeed, that makes no sense. Time may require change to be meaningful, but change is not what it is.
The claim isn't about how we conventionally use language.
Those terms do not necessarily imply change or motion, that's just what your claim is. I've already explained to you how time can pass or proceed without any change or motion. So you simply have a faulty understanding of those terms if you think that they necessarily imply change or motion.
Quoting Terrapin Station
I suggested non-physical change as a compromise, a way of resolving our impasse. I would allow that time is a type of change, if you would allow that the type of change which is time is, is non-physical.
Quoting noAxioms
That's pretty close to what I've been trying to tell Terrapin, change requires time, but change is not what time is.
Can you give a clue re a few words that the explanation started with so that I can look it up again?
Otherwise, re "pass" and "proceed" you'd have to explain the definition you're using that doesn't involve change or motion. And re "nonphysical change" you'd have to explain what that is so that I can make any sense of it.
It's the post where you focused on my claims as to what physicists have determined rather than on the content of the post. Here's the specifics. "Change" and "motion" refer to activities of physical things. As per my explanation in that other post, time can be passing (proceeding) without any change or motion occurring. Therefore "pass" and "proceed" (as in what time does) do not necessarily imply change or motion.
If you want to insist that "pass" and "proceed" (as in what time does) necessarily implies change, then we'll have to allow that "change" doesn't necessarily refer to physical things, and a non-physical thing (time) could change
Quoting Terrapin Station
What kind of nonsense is this? First you asked me to define "pass", so I did with reference to "proceed". Now you want me to define "proceed". I think this will be a never ending (continuous) adventure, as you seem to have difficulty understanding the English language. Nevertheless, I'll oblige you, I mean "proceed" in the sense of "continue".
Quoting Metaphysician Undercover
I'm contrasting this with what Terrapin quotes immediately after:
[quote=Meta]I've already explained to you how time can pass or proceed without any change or motion.[/quote]
So you loosely agree that time without change is not meaningful, but here you say time can pass without any change.
T-S, You seem to defend a definition of time as change, but complain about common language use, which I was not trying to do. I haven't read all your posts, but perhaps you could point to a post where you explain that if that's what you claim.
Yes, I wouldn't exactly say that time without change is meaningless. If that were the case there wouldn't be much point to saying it. I would say that for most, if not all practical purposes, such a thing is useless. But as a logical possibility, and an aid toward understanding the nature of temporal reality, I think it's meaningful.
I'm not clear on your comment.
I'm saying that what time is ontologically is change or motion. That can't be refuted by pointing out that substituting "change" or "motion" for "time" and vice versa in various sentences sounds funny or is ungrammatical, because the argument that "what time is ontologically is change or motion" isn't about language usage, language substitution, etc. It's about the ontological or metaphysical "nature" of time.
It's like saying that momentum is kinetic energy. An object can't have one without the other, but it doesn't follow that they're ontologically the same thing.
'Change' is better than 'motion', the latter being just a subset of change. The paint on my house fades over time. That's change, but not motion. I can also have change without time: The air gets thinner with altitude: change over altitude vs change over time. Change seems not to be ontologically equivalent to time.
What would you mean by "twice as much motion"? I'm not saying that doesn't make sense, but I'm just not sure what would be an example of that.
Re this:
Quoting noAxioms
What exactly is changing in that example? The air density at a particular altitude isn't changing, is it? It seems like you're conflating change and comparative difference there. Comparative difference is conceptual, abstract.
Two equal size wheels spinning, and one goes around twice as fast as the other. That seems to be twice the motion (change) in the same time. The one changes by 2 degrees while the other changes by 1 degree, and if change were equivalent to time, the one must take twice the time of the other to do that.
Okay. That makes sense but you're just pointing out that time is relative (in a different sense than the special relativity sense) to whatever we're using as the change for measurement. In other words, "In the same time"=you have to be referring to some set of changes that you're using for the relative measurement. For example, the changes in a clock.
If you were using the wheel that goes around twice as fast as the change for (time) measurement, then it would mean twice as much time.
Normally we try to use changes that seem phenomenally regular to us as the change for (time) measurement, but we wouldn't have to. It just has convenience for us.
Yes, because if y cannot fail to have x, then x is part of what y means .
"Phenomena is always changing" is analogous to "Every rod has a length"
So just has we can eliminate the concept of length by only referring to rods, we can eliminate the concept of change by only referring to phenomena - where "phenomena" means to refer to the world in general.
I think those arguments are inane. I don't understand the "if y cannot fail to have x" part of your comment, though.
We're also probably not going to agree on what meaning is.
Don't understand what you're saying. It doesn't need to be any particular amount of time for the one wheel to change twice as fast as the other. I chose rotation because rotation is absolute, not relative to anything. Sure, there are two wheels and thus there is a relation to them, but I didn't need to specify the relation with time (the RPM of either) to make my point.
I thought of an example of change without meaningful time: I have a universe with an unstable particle. It eventually decays. The time it takes to do that is meaningless.
I have a million such particles, and at some point, x% of them have decayed. Is there any meaning to a half-life of them? Is there meaning to the concept of half-life at all, as distinguishable from just a list of the order in which the million particles decay? The latter is just a numbered list. I don't see how 'time' has any effect on that where it is meaningful to assert that a lot of particles decay at first, but the last ones take much longer between decay events. Maybe the curve is the other way around and the final ones take place 'close together'. There would be no way to distinguish that model from another.
Right. You asked if it's twice as much time. The answer is yes, if you're using the faster wheel as the time basis. We always use some changing phenomenon (or phenomena) as our time basis (when we're making measurements like this, which is the context you're presenting). Other changes we measure relative to whatever we've chosen as a measurement changes. Changes are always relative to other changes.
Quoting noAxioms
Talking about time in the sense of measurement there, if that's all you have in your universe, "the time it takes to decay" is simply whatever unit you apply to the change in question.
Quoting noAxioms
I don't really understand what you're asking there. Because I don't understand how you're using "meaning" really. If you're literally talking about semantics, meaning is subjective. It's a mental act of association. So are you asking if someone (who?) performs associative acts in that situation?
Then you're relating processes anywhere to that wheel, and not to time.
I don't understand your comment.
When we're talking about measuring time, we choose some changes as the basis. I already explained this.
We then measure other changes relative to the changes we chose as our measurement basis. We could use the relatively twice as fast wheel as the measurement basis. We could use any changes as the measurement basis.
There can be no units. There is nothing on which said units could possibly be based.
There is no simulation. It is a universe with ordered events.
It's always based on some set of changes. You posited a change in the universe. So it would be whatever you assign to that change.
Re "So are you asking if someone (who?) performs associative acts in that situation?"
Quoting noAxioms
I don't know if you read "situation" as "simulation"?? I have no idea what your response amounts to otherwise.
The change is the decay of one of the particles. Not sure what you're thinking I'm assigning to that change other than the order in which it occurs. It is meaningless to say they decay at a fast rate at first, and tapering off. That case is not in any way distinct from them decaying slowly at first, and quickly at the end.
You were positing something decaying at different speeds where there's only that particle decaying? That wasn't clear from your earlier comment.
"At different speeds" would be nonsensical in that situation. "At different speeds" has to be relative to another change.
I had one particle at first, but immediately moved on to the example of a million such particles.
Agree. My example illustrates that: change without meaningful time. Time is not equivalent to change.
You're ignoring the issues I brought up re "meaningful."
If you're going to base an argument on that idea, you can't ignore those issues.
What post again? My take on something being meaningful is that X is meaningful if there is a distinction between a system with X and a system without X. A distinction other than the presence of X.
So I can assert that all hairs on my head have a virtual serial number, and sure, that is distinct from a universe without that because the hairs there don't have a virtual serial number, but there is no distinction to me. I cannot test for which universe I'm in. The serial numbers have no effect on anything. Thus they are not meaningful, in the way I mean that word.
This is what I wrote: "I don't really understand what you're asking there. Because I don't understand how you're using "meaning" really. If you're literally talking about semantics, meaning is subjective. It's a mental act of association. So are you asking if someone (who?) performs associative acts in that situation? "
And then you responded with something about "simulation" for some reason.
If you want to make an argument to the effect of "time can only be change if that (that=maybe time, change--whatever you'd need) has an effect on something" or "time can only be change if there is a distinction between a system with x and a system without x" or whatever you'd want to claim, then I'd check out the argument, but you'd have to make the argument.
OK, I think I described how I'm using the word in my prior post.
Heh... I read you wrong. You said 'situation', not 'simulation'. So much for the eyes.
Quoting Terrapin Station
There is nobody performing acts in my scenario. There were only the million particles.
I didn't really define time. I just brought up points that seem to find flaw in equating time with change.
If anything, time seems to be meaningless without change, but change is not necessarily meaningless without time, so change is arguably more fundamental. Meta might think otherwise since he asserts meaning to time without change, but I find that scenario to be indistinguishable from the same lack of change without the time.
Without an argument, it just seems like arbitrary ideas that have a non sequitur connection with what I'm claiming.
I'm not proposing anything. I'm finding inconsistency in your proposal.
My proposal has absolutely nothing to do with effects on anything or distinctions between systems.
Also, it's not a proposal. It's an identification.
OK, I was finding inconsistency with "I'm saying that what time is ontologically is change or motion". Your 'proposal' is perhaps something else. I was finding a counterexample to the quoted statement there.
It's not inconsistent with having an effect on anything or differences between systems, because I didn't say anything about that.
So what would it be inconsistent with?
I brought up effects and differences and distinctions and such. It is my counterexample.
My example showed something where change was quite measurable but time was not, and if the two were ontologically the same, then if you could measure one, you should be able to measure the other.
How did your example show that? I certainly didn't agree that it showed that.
You can measure change: A count of the particles that have decayed. You have not proposed a way to measure time from that.
A count of the particles that have decayed would not be a measurement of change, by the way. Again, comparative difference is not the same thing as change. I pointed that out with the atmospheric density example.
You can observe decay by observing the changes in a particular particle, say (whether it's just replaced by another particle or whatever). Or if you have a number of particles, you can observe their changing relations (spatial orientation for example) or whatever you like.
The way we measure time from any change is by assigning numbers to the changes in question. So that's what you'd do.
If time was distinguishable in the million-decay example, then you could distinguish the events running forwards (with half of the decays happening before the first half life) from the scenario in reverse, with most of the state changes happening near the end.
There's not really any "forwards and backwards" in time. We just imagine/fantasize about that. There are just changes that happen, and changes can relatively happen at different rates.
Ah, a different definition of change. Perhaps that is the fault in my example.
My original point was that I cannot make sense of the notion of unchanging phenomena, so "phenomena changes" is a tautology that says nothing. One might as well have said "phenomena is phenomena" or "change is change".
So to my mind, there isn't room for two concepts, namely that of phenomena and that of temporal change. Furthermore, when we learned the meaning of the words "changing" and "unchanging" we learned it with reference to public semantic conventions, and not directly in relation to immediate experience.
The two words are different. Phenomenon implies an experienced thing, whereas change does not imply experience. So two concepts, since it makes sense to speak of non-phenomenal change.
'Temporal change' is not necessarily the same as change. Perhaps Terrapin thinks otherwise, since my example of a non-temporal change was dismissed. But equating change to only temporal change seems begging the equality of change and time, not evidence of two being the same thing.
I think change is simply a difference in one variable as a different variable is altered. So one can plot the brightness of my house paint over time, but not necessarily over time, and it presumes a sort of identity of the thing labeled as 'the brightness of my house paint' that can be evaluated at different points in the variable being altered.
Then also, if my house doesn't fade, then the brightness is not a function of time, and it is meaningless to speak of the time at which the brightness of it was value X.
sorry, perhaps i should have been clearer. I'm referring to change within the context of 'phenomenal change' and it's relationship to the A series, as opposed to mathematical representations of change, and arguing that the A series deflates away.
When people say things like "time flows by" they appear to imply that the phenomena of a river is different to the passage of time, something that comes about by first distinguishing phenomena from the A series and then equivocating the A series with the B series to give time an illusion of hidden dimensionality above and beyond what is observed. A flowing river isn't merely a metaphor for time passing, for they are the same thing. "time flows by" just means "the river flows" here. This is entirely consistent with any mathematical description of physical change.
If it can be proven logically that it is possible for time to pass without any changes occurring, therefore no means of measuring that time, then by the impact of that logic, this "possible" time, during which no changes are occurring, is meaningful. Logical possibilities are meaningful.
Of course, that couldn't be proven logically.
It's very simple to prove it logically, (as logical possibilities are very simple to prove as logical possibilities). And I did prove it logically, it's in that post where you focused on what I claimed physicists have demonstrated, rather than on the content of the my post. And the fact is that logical possibilities are meaningful. So the concept of time passing without any change by which that time could be measured, as a logical possibility, is meaningful.
Obviously I don't agree that you proved this logically, but given the sort of thing you seem to be shooting for, all I'd have to do to prove logically that you didn't prove it logically would be to say that just in case I don't feel that you proved it logically, then you didn't prove it logically. I don't feel that you proved it logically. Therefore you didn't prove it logically.
What you "feel' about something is irrelevant as to whether that thing is a logical proof or not. You didn't address the proof in that post, so as far as I know you didn't understand it or perhaps didn't even read it. So what you feel about it is completely irrelevant
Man, you really, really don't understand what logic is.
I know enough about logic to know that the way you feel about a logical proof is irrelevant to it.
What would the formalization of my argument be?
You have no argument, only a feeling. That's why what you say is irrelevant to logic.
Actually it's a simple modus ponens. If p then q. P. Therefore q.
You guys mean something like this: https://www.pdcnet.org/jphil/content/jphil_1969_0066_0012_0363_0381
Time passes but without change?
So, have you read the article?
Yes, that's what I was arguing. It seems quite clear that it is a possibility. All you have to do is assume that there is a limit to the shortest time period required for change to occur, then conceive of an even shorter time period. In other words, even the smallest possible change requires a quantity of time, and we can always conceive of a shorter period of time. For example, if change requires a Planck length of time, we can still conceive of a time period of less than a Planck length. In that shorter time period no change would occur.
Looks like you have to pay to read that article.
If you're requiring soundness you had no argument either. Because it's false that time is anything but change/motion.
I'm familiar with the Shoemaker paper. When the freezes coincide, no time passes anywhere until the next thaw. The only sense in which time passes when one freeze (but not all) occur is from the perspective of one of the zones in which a freeze does not occur. Time does not pass in the zone where the freeze occurred.
I know that's how you feel, you've already made that quite clear. However, with no intent to hurt your feelings, I must tell you that your feelings are quite irrelevant in this matter. So you might just pull your heart off your sleeve and discuss the issue rationally. This is not the place for special pleading, you've produced no argument for your assertion. I produced an argument to back up my claim and you rejected it on the basis that you feel it is false.
Producing an incoherent argument is worthless.
The problem is that I couldn't care less if you don't realize that time is the same thing as change/motion. All it takes is simple observation re what we're doing--functionally, that is--whenever we're referring to or utilizing time in any manner, combined with the complete lack of evidence or coherent argument that time could be anything else. But there's no reason that I'd particularly care if you don't realize this. It's not my problem that you'd have false or incoherent beliefs.
You saw what NoAxioms wrote, we don't use "time" and "change" in similar ways. you're assertions are completely wrong.
A la you're thinking that I'm saying something about conventional language usage?
I don't know what you're saying. It appears nonsensical according to conventional language use, and the philosophy I've studied. Yet you keep asserting it over and over again as if it's meaningful, without backing up this claim with any sort of argument od explanation.
Time is not change, it's a parameter of measurement of change. So your claim that time is change is just like your nonsensical claim that size is an object. I really cannot see how it makes sense to you.
Moreover, because most all of your equations in cosmology are not arrow-of time designated, the equations therein are reversible: ie not only Einstein, but also The Schrodinger and back to laPlace.
What also seems evident is that the process of Emergence itself gives the arrow of time that's not present on a lower level.
You misunderstood, the time difference with the traveler and the time passed on earth is only 1 second, though to travel 1 second into the future compared to the rest on earth took a year. When we talk about time travel we usually means creating a difference in experienced passing of time compared to the ones experiencing the regular pace of time on earth.
Quoting noAxioms
Maybe a typical assumption, but since there was no indication that this was intended, it could just as well mean time travel to the future. Theoretically we can even travel to the past, our scientific models allow for that, it just requires some practically impossible implementations at the moment.
Quoting noAxioms
high speed is just one of the options, being subjected to a different amount of gravity also works, hence strictly spoken your head ages quicker than your feet since your head is subjected to less gravity than your feet on earth when standing up straight.
The higher your speed, the slower time goes for you, if travel at the speed of light, time stands still. The more gravity the slower time goes for you as well.