Does Relativity imply block universe?
So a presentist walks into a spacetime bar, and the wormhole behind the counter asks: "Why so tense?"
This is a split of a side discussion in another thread (starting here), which I thought merits its own topic. I will just quote from some posts and continue here.
Some background:
Kristie Miller, Presentism, Eternalism, and the Growing Block, A Companion to the Philosophy of Time (Wiley, 2013)
David Ingram, Presentism (Stanford Encyclopedia of Philosophy)
Steven Savitt, Being and Becoming in Modern Physics (Stanford Encyclopedia of Philosophy)
Dean Zimmerman, Presentism and the Space?Time Manifold, The Oxford Handbook of Philosophy of Time (2011)
This is a split of a side discussion in another thread (starting here), which I thought merits its own topic. I will just quote from some posts and continue here.
Some background:
Kristie Miller, Presentism, Eternalism, and the Growing Block, A Companion to the Philosophy of Time (Wiley, 2013)
David Ingram, Presentism (Stanford Encyclopedia of Philosophy)
Steven Savitt, Being and Becoming in Modern Physics (Stanford Encyclopedia of Philosophy)
Dean Zimmerman, Presentism and the Space?Time Manifold, The Oxford Handbook of Philosophy of Time (2011)
Comments (102)
Quoting Douglas Alan
Quoting Douglas Alan
You have to be careful when you say "different times," unless they are all on the same worldline, which is not the case here. From what I gather (and I have to admit, I hadn't encountered this type of objection before; the most common objections from relativistic physics have to do with the relativity of simultaneity in Minkowski spacetime), closed time-like curves and some other other topologies that are theoretically allowed by GR are a prima facie problem for presentism because they cannot be foliated (i.e. you cannot slice spacetime along constant-time hypersurfaces). And even if we stay with one worldline, closed time seems to imply that there can be no objective "pastness" and "futureness," as the traditional A-theory requires. But it is still possible to recover a local surrogate of presentism even in a spacetime with time loops - see for instance Steven Savitt, Time Travel and Becoming (2005) and Phil Dowe, A and B Theories of Closed Time (2017). A more common response for a presentist though is to deny that such non-foliable spacetimes are (meta)physically possible, and that is a defensible position, since we don't know for a fact that they are.
Outside of closed time-like curves though GR - specifically, the GR of our universe - is said by some to be more hospitable to presentism than generic SR because its symmetries naturally lend themselves to defining special reference frames and privileged observers (e.g. the rest frame of local matter or the CMB), and those are said to be good candidates for defining objective now. (I don't think I buy this argument myself.)
Quoting Douglas Alan
There is some truth to this, but if you haven't yet surveyed the extensive literature on the subject, then perhaps the review articles that I posted at the top will go some way towards disabusing you of the notion that this is a settled issue in philosophy.
Dean Zimmerman writes: "The A?theory is almost certainly a minority view among contemporary philosophers with an opinion about the metaphysics of time." (He frames presentism as a variety of the A theory.) "Nevertheless, it has many defenders—Ian Hinckfuss, J. R. Lucas, E. J. Lowe, John Bigelow, Trenton Merricks, Ned Markosian, Thomas Crisp, Quentin Smith, Craig Bourne, Bradley Monton, Ross Cameron, William Lane Craig, Storrs McGall, Peter Ludlow, George Schlesinger, Robert M. Adams, Peter Forrest, and Nicholas Maxwell, to name a few." He notes further:
Quoting Dean Zimmerman, Presentism and the Space?Time Manifold[/url], The Oxford Handbook of Philosophy of Time (2011)
Laying my own cards on the table, I am not a proponent of either A- or B-theory, eternalism, presentism or possibilism; rather, I suspect that there isn't a substantive difference between them. But I've only dipped my toes into this subject on occasion, so I haven't made up my mind.
Quoting Douglas Alan
I do, in general. For one thing, scientists rarely consider the same questions as philosophers. Their approach tends to be instrumentalist; excepting those few who work on foundations (which is widely considered to be a philosophical subject among scientists, and thus widely discouraged), they favor questions that can be resolved empirically, rather than through conceptual analysis or other approaches employed by philosophers. Nearly all the literature on this subject that I have come across was written by philosophers, many of whom understand the relevant science very well (for such general questions the scientific underpinnings aren't that difficult or esoteric). And scientists who do opine on philosophical questions are subject to the same competence limitations as other laymen.
"We can't see this block, we're not aware of it, as we live inside the cement of spacetime. And we don't know how big the block universe we live in is: "We don't know if space is infinite or not. Or time - we don't know whether it has a beginning or if it will have an end in the future. So we don't know if it's a finite chunk of spacetime or an infinite chunk."
thats a quote from:
https://plus.maths.org/content/what-block-time
Time can never be measured exactly (or to be more precise, universally) because time is effected by the speed the measuring device is traveling at(clock). I read the book "a brief history of time". Because nothing ever exceeds speed C, to put it simply the various vectors of the whole of an object, slow down so that the combination of the vectors never exceed C.
To my limited understanding, Einstein based his theory of Relativity on the idea that we live in a block universe. I don't know if this belief has changed alot in the past 100 years or not. Nor do i even know if that first statement in this paragraph is valid. I'll read those 3 articles later.
I tend to towards the threshold of eternalism (to my understanding of eternalism). However i see the universe as just a collection of objects and particles (with a "web" of emotions going through it to put it overly simple). When particles move the only way to measure that movement accurately (in terms of speed as opposed to angles and geometry) is within a small subset of the universe (a given area of space). The only way to go back in time is to place each particle back in the same position only relative to the other particles as it was in that remembered time in the past. The vectors or paths of motion also have to be exactly the same. Our memories are extremely rough notions of what the past really was given all the variables involved in solidying exactly what the past was.
This is wishful thinking on your part. People like to watch movies but the reason Physicists typically stick to very slowly (using software) finding a more precise number to attach to an important variable, is that alot of the "fun" stuff ended with Einstein. Einstein was a genius but as time progresses, the type of work that has to get done in a given field of study changes.
OK, you didn't say 'demonstrate', but it very much suggests it anyway. The vast majority of non-religious physicists that know their relativity (many (most?) probably don't) hold a block view. The view is semi-incompatible with the promises of major religions, and thus meets significant resistance without actually admitting the reason driving the resistance.
But what's the relationship between the block universe (a physical model) and the metaphysical interpretation of time? It seems to me that there are two different "natures" of time: how time operates in our best predictive models, and what this means. Those two shouldn't be mixed.
No, relativity does not assume any of the questions that are at issue, such as whether the present is in some sense more "real" than the past or the future, or whether past, present and future tenses are objective properties and not merely indexical. Some argue that relativity makes anything but the block universe untenable, but not because that is already assumed by the theory.
To be clear, "block universe" in this context is not merely a visualization of the spacetime continuum (in Newtonian physics you can also visualize the space and time dimensions as a single block). Here it is a synonym for the B-theory of time or for eternalism, which are metaphysical positions.
Yes, that is a question that is often glossed over. Scientists in particular often implicitly assume the stance of scientific realism when talking about time, i.e. that all and only those things that are posited by our best scientific theories are real (or something like this) - which is natural, since methodological realism, which we assume when doing science, and metaphysical realism are easily confused. But whatever the merits of this position, it is a philosophical position and must be acknowledged and defended as such.
It is uncontroversial that physics in general, and relativistic physics in particular does not endorse presentism or the A series. But what conclusions are we warranted to make from that fact?
I mean also unicorns, dragons and God/s can be real in some sense...
Sorry, but I consider them to be the same model, both metaphysical interpretations of space and time.
If that's the case, why is it of particular note what the majority of physicists thinks?
I for one know my physics enough to know that I've never seen an empirical falsification of either interpretation, and hence any logical argument must proceed from non-empirical assumptions. I've done that process and concluded what I conclude, but my stance keeps changing as I learn more, so the odds that my current favored view corresponding to 'the way that it actually is' (if there is such a thing) is pretty minimal.
In what sense do chairs live outside the mathematical equations?
|>ouglas
oh ok. I don't have a strong opinion at this point. To put it simply, i believe whatever form of block universe we live in, that scientific determinism determines all of our actions. Any future decisions are based on what we learned from our own actions or what we observed in the past. Some would say the past present and future exist all at one time, however i would say that all depends on "how big you are". This guy you are talking to exists now. Perhaps there are others on this forum who are "bigger".
I take it that nothing is ever settled in Philosophy. But I've also noted that if you swim against the tide, the onus then is usually on you to make a very strong case, and if you swim with the tide, you need say little to defend your position.
Does this make the tide necessarily right? Of course not. Tides change from time to time, and philosophical debates can rage for thousands of years. But if we are to believe that Philosophy is of any use at all, other than just as a means of honing one's ability to think and argue well and coherently, it seems that one must be committed to the belief that following the tide is the path that is generally most likely to lead to knowledge.
I did some skimming of the references you provided that were actually available to me. One thing I noted that was of interest is that in a closed timelike curve, there can be no consistent entropy gradient that gives time its forward arrow. If there were such a gradient, you couldn't return in the loop to the same point in space-time, since that point must have the same entropy, and consequently it wouldn't be a closed curve. It seems that this would make traveling around one unpleasant. But, I suppose if it were large enough, you could refrain from going all the way around the loop, and I suppose there could be a gradient that does not change direction in the part that you stay on. Well, this is probably neither here nor there for this discussion, but I found it an interesting worry.
So, I've been thinking about time-traveling wormholes instead. Let's say that you enter a wormhole headed for the past. Your lovely wife died and you are heartbroken. You wish to be with her again. While you were with her, she mentioned that she had had a wonderful boyfriend in the past who was a lot like you, only older. Unfortunately, he eventually died in a freak gardening accident, but they had been very happy together for many years while he was alive.
You decide that you must have been/will be this man, and so you enter the wormhole and begin your new life as your dead wife's sugar daddy. Only she's no longer dead from your new location in time.
So what is happening here with respect to existence? We already know the eternalist view, so I will elide that. But there are two other possibilities that I can think of:
(1) When you enter the wormhole, reality splits in two, and now there are two presentist universes. Though they are both on deterministic rails. Such a split happens every time someone enters the wormhole. Oh, but wait? What about random particles that enter the wormhole. Do they cause a myriad of forking realities?
I find this view to be highly unsatisfying.
(2) Presentism is correct and the only existing point in time is now. When you enter the wormhole you cease to exist. I.e., you die. You committed suicide. It's really very tragic.
But to soften this tragedy, there was a time in the past when there were two of you. Unfortunately, one of you just appeared without any cause or history, and so this mysteriously appearing version of you is not really you at all, but rather a weird clone of you made by space and time out of nothing but random particles and energy.
When you entered the wormhole, you were hoping for a continuity of consciousness. You expected to be traveling into the past. But nothing could be farther from the truth. You died. Nothing more. And it just so happens that someone else just like you, but not you, was brought into existence, at precisely the time and place you wished to travel to. Not only is your suicide a tragedy, but it is compounded by the fact that in the distant past some imposter got to spent all this wonderful time with the woman of your dreams.
I also find this view to be highly unsatisfying.
|>ouglas
We get a sense that some theoretical entity is more than a mathematical contrivance if it does not go away when we change the model, i.e. if we find it indispensable. Our sense of the reality of the thing also strengthens when we find more independent ways of probing it with empirical tests. However, these criteria are not so solid and there is room for much ambiguity in edge cases. Physicists do not usually obsess over questions of whether something is really real or somewhat real or not quite real.
In the latter case, indeterminism only holds for the most widely adopted interpretation of QM, the Copenhagen interpretation, but there are others. For instance, one can preserve determinism by incorporating some form of non-locality, as in Bohmian mechanics. One can also introduce multiple parallel universe as in Many Worlds as well. They're all equally valid ways of understanding QM as far as the scientific theory goes.
Though less well known (perhaps on account of the fact that Relativity isn't notorious for having 100 different interpretations unlike QM) the same goes for both SR and GR. One can introduce a preferred frame (or foliation) to designate an absolute sense of time, and that'd be compatible with the scientific theory so much as it doesn't make any differing empirical predictions. In fact, one of the predecessors to SR was an empirically equivalent model that included an absolute frame called the Lorentz Ether Theory. With respect to GR, there are also alternative formulations like Shape Dyanamics which incorporate an absolute time in exchange for absolute scale.
Of course there are questions about whether we should introduce such additional structure in the first place to account for our traditional sense of time, but that's a question of metaphysics, not physics.
A Physics Forums Insights article I've found useful is The Block Universe – Refuting a Common Argument.
Essentially:
(1) Relativity of simultaneity + all observers' 3D worlds (surfaces of simultaneity) are real at every event = block universe
The point of contention is generally the second premise. However experimental results that demonstrate relativity of simultaneity can only be communicated at the speed of light, and all such communicated events are in the observer's past light cone. So the second premise is unnecessary - the following is sufficient to account for our observations:
(3) All events in the past light cone of a given event are real (i.e., fixed and certain) for an observer at that event.
Since the second premise is unnecessary, Relativity does not imply a block universe (at least on that argument).
As David Mermin puts it:
Quoting David Mermin, It's About Time
This also brings up another relevant question: does the coordinate time of a mathematical model (in this case the theory of relativity), physical time (time that is measured by physical clocks) and metaphysical time always coincide? I am more than a little skeptical of the metaphysical time (as distinct from the other two), although some A-theorists find themselves more-or-less forced to assume it in order to rescue the hypothesis. But as for mathematical vs. physical time, hypothetical time loops in GR spacetime may be one of the instances where they pull apart. And they highlight a problem with relativity as a model of time: relativity does not have a concept of the arrow of time. Sure, the coordinate time has two opposite directions, but there is no fundamental distinction between them; the designations of "future" and "past" are purely conventional in the model. If what you are saying about closed timelike curves is correct, it appears that even as the physical time reverses its flow, the coordinate time does not notice the fact, merrily ticking along. (Another interesting question is what happens after the heat death or, in some models, at the Big Bang, where physical time may effectively disappear, even as coordinate time goes on. But that is a discussion for another time, as it were.)
Relativity does have the concept of the passage of time, and notably it admits differential rates of time, when the duration of proper time is shorter along some future-directed worldlines than others, as in the twins paradox - in effect giving us future time travel. The way we, as empiricists, can know that this really does capture at least some aspects of the flow of time is that this is something that has observable physical consequences: the differential rates of time's passage can actually be marked and recorded by physical clocks in properly conducted experiments. But the question remains: are there limits to the fidelity of this model when it comes to describing time?
I am not yet sure what to make of past time travel. Not surprisingly, there is plenty of literature on this issue as well, including discussions of causality paradoxes (see for instance SEP articles on time, or Kutach's article in A Companion to the Philosophy of Time, or Smeenk and Wüthrich's article in The Oxford Handbook of Philosophy of Time). But I think I'll leave this can of worms for another time...
In spatial terms the matter of events occurring in the same place (the "now" of space) appears to be nebulous; as the "size" of the space varies, the number of events occuring in the same space (the "now" of space) also varies. The rule of thumb seems to be that as the space available is increased the number of events that are spatially "simultaneous" also increases and upon downsizing the space, the number of events that can occur in that region also decreases until, it seems, at a single point in space only ONE event can occur.
For time the situation is quite different. Yes, increasing the time-period results in an increase of the number of events in that zone of time but, unlike space, reducing time down to a single instant doesn't limit the events possible down to ONE: many, possibly an infinite, number of events can occupy a single moment in time.
The "now" of time is not limited in the same way as the "now" of space. Simultaneity is simply the temporal concurrence of events at a single instance of time. It maybe obvious that moving along the time axis we may have an infinite number of events at a single point in space. Does this mean that moving along the space axis we can have an infinite numner of events at a single point in time? Yes.
My concern is how simultaneity defines the present/now? Is the idea of spatial "simultaneity" critical to the definition of a spatial "now"? When I speak of such a thing as the same spot, do I depend on events having taken place at that particular spot? Not really, right? A location/spot is defined in terms of a frame of reference which even if arbitrary has nothing to do with events at all. In other words, while different events may occur at the same spot, that they do has nothing to do with the notion of a location/point in space.
Likewise, a temporal spot, the present/now, shouldn't be predicated on the notion of simultaneity which is basically events that occur at a particular moment. The now/present, like a location in space, is defined, not by any feature of events like simultaneity, but by a frame of reference and how any particular point, spatial or temporal, exists in relation to that frame of reference.
I guess I don't see the relevance of simultaneity to the definition of the present/now on the basis of some kind of symmetry between space and time.
However, it can be said that there is no ONE "now" in time and that is demonstrated by the difference in the set of simultaneous events as the frame of reference varies.
I think you're just saying that relativity doesn't entail an arrow of time, nor is it dependent on there being one. Nevertheless, relativity is consistent with there being an arrow of time. Relativity is not a theory of everything.
For example, after extensive paraphrasing, the blogger ends up with the following thesis:
(1) Relativity of simultaneity + all observers’ 3D worlds are real at every event = block universe
I take it from the context that "observers" here are not meant literally, but rather as virtual probes that could potentially be dropped anywhere within the spacetime block. Oh, wait. Well, he does go on to state the obvious: that the second premise already presupposes the conclusion. But then for some reason he backtracks and adds that the first premise is needed as well, although he doesn't explain why.
I appreciate that Presentism has many problems of its own, but it always amazes me that proponents of Eternalism so readily accept the static, motionless nature of their own temporal landscape. I'm no scientist, but much of science appears to be reliant on a dynamic world involving rates of change, momentum, spin, acceleration, velocity, etc.
This is more evidence for eternalism if you ask me. E.g., why is it that "metaphysical time" just happens to agree with the arrow of time placed by the direction of increased entropy? What a fortunate coincidence, since it would be a crazy world otherwise.
For eternalism, there is no problem here.
On the other hand, I guess presentists could just say that the world had a 50/50 chance, and fortunately, it came up heads.
|>ouglas
P.S. Or maybe presentism is true, but metaphysical time is actually reversed from the direction of increased entropy. Maybe we are constantly hurtling forward into the past without even knowing it!
Except that an arrow of time assumes a dynamic world?
The argument is simply that relativity of simultaneity isn't sufficient by itself to imply a block universe. An additional premise is required, which is that all events to the past of any observer's surface of simultaneity are fixed and certain.
Observer is just being used in its common physics sense - an inertial reference frame. But the specific example referenced - the Andromeda Paradox - has sentient observers.
The "paradox" says that the alien invasion launch is already fixed for one of the people on Earth (since it is in the past of their surface of simultaneity). But this conclusion assumes the above additional premise. Moreover, the alien launch is not in the past light cone of anyone on Earth, it's in a spacelike separated region. So there is no reason to conclude from Special Relativity that the alien invasion is fixed for observers on Earth.
BTW the Physics Forums thread for that article is at:
https://www.physicsforums.com/threads/the-block-universe-refuting-a-common-argument-comments.843000/
Quoting SophistiCat
Well if relativity of simultaneity is rejected, i.e., simultaneity is absolute, then every observer has the same surface of simultaneity which then doesn't imply a block universe. So both premises are needed to imply a block universe.
Quoting Luke
I don't think the typical eternalist would assert a motionless landscape. An object is here at time zero, and over there at time 1, thus there is motion, spin, acceleration, velocity and all that.
Quoting LukeThe block view does not lack dynamics. The arrow of time kind of assumes that view since I don't see how you can draw an arrow in a direction that is posited not to exist.
I agree, and I think that this is an underappreciated point. Note that relativity is compatible with absolute simultaneity as well* - it just doesn't require or entail or suggest one. Just as the arrow of time would be an extra structure not licensed by the theory, so would simultaneity.
Does the fact that a feature is not required by a theory, even such a universal and well-supported theory as the Theory of Relativity, imply that it is not a real feature of the world? Not necessarily. It depends on whether the theory was constructed and tested in a way that would be sensitive to the existence of this feature. Since Relativity is agnostic about simultaneity, it doesn't give us an unambiguous answer. But this does put the pressure on the A-theorist to supply a justification.
* Time loops that are possible in GR make global simultaneity problematic. But first, we don't know if they actually exist - all we know is that they are compatible with GR. And more importantly, I don't think that global A-properties should be a requirement for A theories; local properties should be enough, given the phenomenology to which their proponents appeal.
Not sure what distinction you are drawing here. Are you suggesting that, unlike the presentist, for the eternalist the nature of space and time contains nothing over and above that which follows from the theory of relativity? (And so for the eternalist there is no such thing as the arrow of time.) I am not so sure. At least I don't see why the eternalist has to be so exclusively committed to the relativistic spacetime.
But yeah, the arrow of time is another can of worms.
Alas, I'm not sure where the confusion is arising. If you believe that GR entails eternalism, the forward direction of time is given straight-forwardly by the direction of increasing entropy. (Modulo situations in which there is no such clear direction, such as post-heat death of the universe. But since there won't be philosophers existing then to worry about the problem or to experience what it is like to live in this time, this would seem to be moot to an eternalist.)
If you are a presentist, you could, it seems to me, be possibly be living in an unfortunate world where the time that exists is moving in the direction opposite to the direction of increasing entropy. The laws of physics work either way, so how could you know that this isn't the case?
|>ouglas
An arrow for time does not preclude eternalism. It is the direction of increasing entropy.
|>ouglas
Why is it not the direction of decreasing entropy? What difference does an arrow of time make in a static world?
Matter is not only material but logical, meaning that there is, inter alia, some weight.
Doesn't this imply at least a second mechanism as part of the universe?
Block universe is material only, and this block would have no strength to contain weight.
Metaphorically, the way is part of the universe shape. You would think more abstractly but also accurately.
In my language, universe being super massive means massive-mark or wound. You would think of the universe as something you know in districts, not as 1, it's too massive. It's a freak of size but not of technicality. Even one perception proves districts, because you would at least have to look around to get a full view of all stars.
We are giant creatures who traverse even their bodies.
When you imagine the universe for it's all you imagine a wound in your mind and this is more directly is an accidental hit of a mental goldmine, when purposefully exposed is a grade lower.
It's coming off right, wrongly. When you try to come off right, rightly, you approach this moment wrong and thus it's harder to be right and can be less easily maintained. And thus, good thought.
Because the way that entropy works implies that people (and computers, animals, etc.) will remember the past and not the future, where the past is defined as the direction of decreasing entropy and the future is defined as the direction of increasing entropy. This is just how physics works, emergently.
|>ouglas
This seems to assume that "entropy works" in a dynamic way with a moving present moment, and that we are able to remember past times but not future times relative to that moving present moment. That is a presentist assumption. What is the eternalist account?
The eternalist account is that at every point in time, a cognitive entity can remember events from the past and cannot remember events from the future, relative to that point in time. (Modulo certain time-travel scenarios, which are very unlikely in reality.)
|>ouglas
Imagine really fast blue and yellow flashing, crackling almost in harmony. Like the energy of a disc reader. This flashing maintained past and future.
Okay then, how are events 'made present' for a cognitive entity, such that they have a relative past to remember? I'm finding it odd for an eternalist to be using such presentist terms.
I don't understand your question. In an eternalist world, I exist right now, as I am typing this, and I can remember events that happened before right now and I can't remember events that are going to happen in an hour.
There is also a version of me existing who resides at a point in time 15 minutes ago. That version of me can't remember what I am typing right now, because that is in his future, but he can remember my previous response to you.
|>ouglas
I don't really know what to say. It works exactly the same. The only difference is whether you consider the past and future to not exist, which is presentism, or whether you consider that everything that ever happened to still exist and everything that has yet to happen to already exist. If you believe this, then you are an eternalist.
Other than these differing metaphysical theses, which may not be at all provable either way, everything remains the same.
|>ouglas
You seem to want to have your cake and be able to move to eat it too!
I don't have time to read Miller right now. I have actual work to do, which is towards trying to cure cancer. So please forgive me if I'm erring on the side of brevity at the moment.
I did quickly read that staticism is the thesis that the present doesn't move. I find this to be a bit misleading with respect to eternalism. In eternalism, all times are the present in the sense that all places are "here", if that's where you happen to be.
There's nothing in eternalism that precludes things from evolving over time, since in eternalism there is definitely time, and at any given point in time, there are future times and a past times. And things will be different in those future and past times. Hence things change as time changes.
|>ouglas
No offense, but I think that you have taken what has been written at a superficial level and haven't done the work to actually understand it.
If you do understand it correctly, you should probably make yourself aware that this is a philosophical debate that has raged on for decades at least, and there are many full, tenured professors who agree with me. And in fact, some of those full tenured professors taught me what I know about the subject. Which was at MIT, which is considered, last I checked, to have the fourth best Philosophy department in the world.
So if you don't want to take my word for it, take the word of some tenured MIT full professors.
|>ouglas
There is no need. I have read the article by Katie Miller and she has done a perfectly good job of explaining all the issues. I agree with everything she says, except for one paragraph:
I don't believe that anyone on the planet has offered a satisfying explanation for phenomenal consciousness, so eternalists are in no worse shape here than anyone else.
As for why we remember the past and not the future, this follows plainly from thermodynamics. When a computer program runs, it follows the laws of thermodynamics. Computers, like people, remember the past and not the future. This fact is true in either eternalism or presentism because these different metaphysical theses do not at all affect physical law.
|>ouglas
You need to read Miller again. Presentism and eternalism are metaphysical theses. They do not affect physical law. Physical law is exactly the same with either metaphysical thesis. If you understand how physical law works under eternalism, you understand how it works with presentism and vice versa.
Physics itself is completely agnostic about whether eternalism or presentism is true. Though I'd hazard a guess that most physicists would side with eternalism.
(Actually, what I said above is not quite right about Physics being agnostic, since certain aspects of Special and General relativity present serious issues for presentism. Though a presentist can fudge answers that I find completely unsatisfying and ad-hoc. Also the fact that physics is almost completely symmetric with respect to time is another problem for presentism. At least in my opinion. If presentism were true, I think it would be very surprising for the laws of nature to be time-symmetric.)
|>ouglas
Yes, I do.
|>ouglas
Quoting Douglas Alan
You appear to be claiming that things can change and evolve over time, while also agreeing that nothing changes?
You just don't understand these metaphysical distinctions. As I mentioned physical law is identical under both of them. If you don't believe me, write to Miller and ask her yourself. She'll tell you just what I have.
PHYSICAL LAW IS IDENTICAL UNDER BOTH ETERNALISM AND PRESENTISM.
Repeat that to yourself 1,000 times until you understand it. There's no point in having a discussion when you don't understand the basics of the distinctions that are being made.
|>ouglas
You asked how things like bodily functions can work under eternalism. They work under eternalism for the same reason they work under presentism. I.e., physical law (and hence biological law) is the same with either!
|>ouglas
Eternalists have such accounts: Time is real. It is locally ordered. (I word it this way just to account for Special Relativity.) For every point in local time there is an immediately past point in local time and an immediately future point in local time. People, and other representationalist systems, such as fancy computers, can represent the past and the future relative to the point in time where the person or computer is located. They can understand the laws of nature well enough to make certain predictions about the future points in time from the past points in time. They can record information about the past in their memories, etc.[s][/s]
It's no big mystery. The only reason that Miller even says this is because she seems to be trying to write a balanced exposition of the two positions without forcing anyone's point of view. (I assume that this article is for a textbook for students who might then write papers where they argue for one of the two positions.) But if you read her article, you will have noticed that she has many more critiques about presentism. Would you like me to throw them all at you and force you to answer them?
|>ouglas
Another possible response from eternalists is the "spotlight theory". It's in Miller's article, so you can read more about it there.
Under the spotlight theory, such an eternalist will say that time is like a movie reel. It's all there all at once: past, future, and present. Only there's a spotlight that runs down the movie reel illuminating one frame at a time, in chronological order.
Most eternalists will say, "Exactly! Only there's no need for the stupid spotlight."
If you want a version of eternalism that works for you, start with the spotlight theory. And then convince yourself that you don't need a spotlight. Or remain committed to the spotlight if you wish. It's no skin off of my teeth either way.
|>ouglas
Miller writes this:
[quote=Miller]Thus eternalists endorse the following pair of theses:
Eternalist Ontological Thesis (EOT): Past, present, and future times and events exist.
Static Thesis (ST): The present does not move: which moment is the present moment does
not change.[/quote]
Now either Miller has no understanding of the position, or she's talking about something completely different. The view denies the existence of a preferred moment called 'the present' and hence the ST part is nonsense. I've actually heard of such a view, which is presentism without the movement, but Miller doesn't seem to be talking about that since she correctly states that all events at all times exist equally, which is not true of a model with a present that stays put like that.
Anyway, I'd never accept these points as worded. The first isn't totally wrong, but past/present/future are all relations like < = >, and not objective states like negative, zero, and positive, and the wording makes it sound like the latter.
Quoting LukeI'd say there is no 'the present' to do any moving. 'The present' would be just any event's self reference, and that, by definition, cannot move.
Also known in physics as 4-dimensional spacetime. 3D Space and time are separate under presentism.
I haven't seen the dynamical thesis, but this seems right.
The subjective flow of time is an illusion, illustrated empirically with the twins scenario in relativity. If people could detect the actual flow of time, then they'd be able to detect movement due to the subjective slowing of clocks when they're moving fast, wheras if it were an illusion, any traveler would notice no difference. This of course isn't easy to test given the cost of the experiment, but it is there.
No, it isn't a proof of one view or the other, just a demonstration that the flow of time is a subjective illusion.
All you have stated here is that all points/moments in time exist. You have offered no account of why we apparently move in time from one moment to the next; of why we apparently age; of how change and/or temporal flow apparently occurs. I understand that these are very difficult to account for, but you said that eternalists had such accounts. It's one thing to tell me that Paris exists over there and another to explain how I can get there, especially if nothing really moves.
Quoting Douglas Alan
I consider the moving spotlight view to be a hybrid of Presentism and Eternalism, since it contains all times/events (Eternalism) plus motion (Presentism). If you remove the spotlight, you remove the motion, and then you need to account for the appearance of motion. This is exactly the problem for eternalists.
Quoting Douglas Alan
I find the lack of a compelling account for the appearance of motion/temporal flow/ageing to be too problematic for Eternalism. You can pretend as though it's unproblematic if you wish.
It's unclear to me what the illusion is that you are referring to. What 'movement' is going undetected? What 'movement' would be detectable if "people could detect the actual flow of time"?
Do you not detect any motion, notice yourself ageing, or find yourself now at one moment and now at another? If all of that is an illusion, then what is illusory about it? And how do you account for it?
But that would not be sufficient for a block universe either. Unless observers are spread throughout the entire spacetime, their past light cones sweep only part of it, resulting in a moving block. Which is why he adds the stipulation of all observers - meaning, apparently, the entire spacetime block. Which, of course, assumes the conclusion.
And in any case, whether the argument is for a moving block or for the full block, nowhere does relativity do any work here. All you need, according to this argument, is the assumption that there are some observers for whom the past is fixed.
Here is a simple space-time diagram:
Both the presentist and the eternalist agree that the diagram depicts movement of a body through space. But the presentist adds that there is a fact of the matter about where on the diagram the body is right now, while the eternalist says that there is no such fact of the matter (not without reference to a specific observer). Nevertheless, the eternalist will agree with the presentist that the body is located at 10 m from the coordinate center at time 1 s and at 20 m at time 2 s, and that the difference constitutes a change in the body's position.
Then it must also be an "unfortunate" choice of words when Miller describes the B-theory of time as "the view that the world is a static block of events", or that a view which endorses the B-theory "rejects the dynamical thesis", or that "Eternalism...is a static view that rejects temporal flow."
Quoting SophistiCat
Of course there is time in both the presentist and eternalist accounts; they are theories of time. I have never disputed this. If you wish to equate time with motion, then perhaps Eternalism isn't for you.
Nevertheless, I get the message, and I won't interrupt the discussion any further.
GR doesn't know anything about entropy - it's not part of the theory. For those who base their theory of time exclusively on GR - call them "relativity fundamentalists" - entropy is a stolen concept. They have to limit themselves to GR's coordinate time, which increases monotonically (in simply connected topologies), but in an arbitrarily chosen direction. Therefore, if it is possible for the entropy gradient to reverse itself along the length of one worldline, then a relativity fundamentalist faces a problem, because her theory of time is not sensitive to this change. Either she has to add something extra to the theory (which, incidentally, is what presentists do as well and for which they are criticized by fundamentalists), or she has to bite the bullet and say that the direction of time given by the entropy gradient can sometimes be wrong. (And then when is it right - and why?)
In the less contentious heat death scenario physical time effectively disappears, since there are no physical clocks to mark its passage, but the coordinate time continues - another contradiction that can be solved by acknowledging that mathematical time is not identical with physical time.
I understand this. The second law of thermodynamics is not even fundamental law. It is stochastic.
Quoting SophistiCat
For an eternalist, I should not think that this is a problem. Time is symmetric with respect to fundamental law. (Modulo Cronin and Fitch. It's a bit hard to know what to make of this at my level of understanding, but I'm going to put it down as "annoying detail" until someone informs me otherwise.)
Since time in fundamental law is symmetric, it has no forwards or backwards. It just has two different directions that are equivalent, except for the fact that they point in opposite directions. Only thermodynamic tells us which direction is foward and which is backwards. Were one to travel through a strange region of space in which the entropy gradient changed directions, this would no doubt be problematic in terms of how we normally conceive of causality, etc., but fundamental law, including GR, should have no problem at all with it. In GR, time still has two directions, and there is no difference between the two directions, other than which one is heading toward increased entropy. GR and the rest of fundamental law doesn't care about this, however.
Or at least that's how I understand things.
Quoting SophistiCat
I don't see the problem. There are two directions of time. Neither of these directions of time ever changes. The only thing that might change is which direction of time is pointing towards greater entropy could change. But the direction is not changing. Only what is in that direction might change.
Now I certainly agree that having the entropy gradient reverse directions on you has all sorts of potentially unsavory and weird consequences, which, I suppose is one reason that some people think that this will go away when GR and QM are unified.
Others just think that universes where things get too weird in this regard, are just very improbable universes, so we're not likely to find ourselves in one. E.g., typical time travel paradoxes that are not logically impossible. E.g., a being from the future brings you back via a wormhole the solution to clean fusion energy production. In the future, the only reason that clean fusion energy exists is because you published a paper on how to achieve it. The invention of clean nuclear energy production came into existence without any inventor. (Well, I'm sure I'm now belaboring a point that you already fully understand.)
There's nothing in GR that precludes this. But amongst the solutions to the equations of GR, the solutions that include such strange occurrences are much less prevalent than the number of solutions that don't include such strange occurrences. (Yes, I know blah, blah measures on such infinities don't exist, blah, blah. Understanding any of that or how to resolve these objections is beyond my pay grade, but I assume that there is some answer that is something along these lines. I.e., my friend who is a UPenn professor with a PhD in number theory doesn't seem worried about this kind worry, despite the fact that I don't think he can answer the worry about measures in infinite spaces. In fact, he's fully signed onto Tegmark's MUH.)
|>ouglas
The appearance of motion is something that is represented in your brain. Where else would there be an appearance of motion? Since physics is the same under presentism and eternalism, your brain is going to represent the same things under either presentism and eternalism. Consequently, if your brain represents the appearance of motion under presentism, it will do so under eternalism, and vice versa.
As for aging, this is yet again a physical process that works exactly the same under presentism and under eternalism. Under eternalism, you can think of your life as a film roll, and at one end of the film roll you are a newborn baby, and at the other end of the film roll you have hopefully died happily at the age of 107 of natural causes in your sleep. In each frame between your birth and death, there will be evident an incremental bit of aging.
|>ouglas
Quoting GregoryThis is totally wrong. The sole observation from which Einstein did his SR work was the apparent constant speed of light. From that, all the things above were predicted, not measured ahead of time.
Indeed, he didn't do them himself.
Except that there is actually no motion according to Eternalism. I would imagine that it's much easier to explain why we perceive motion if there actually is motion than if there actually isn't. My point, again, is better expressed by Kristie Miller:
[quote = Kristie Miller]For the eternalist, the key challenge lies in explaining temporal phenomenology and in explaining the apparent directionality of time. There has been significant work in this area, but questions still remain: why do we have such a different relationship with the future than with the past: why is it that effects typically precede their causes when the laws of nature are symmetric: why do we remember the past, but not the future: why does the present seem to us to have a particularly salient quality that other moments lack; what are the cognitive apparatuses that underlie our experience of temporality and how do they function to create temporal phenomenology; what is the evolutionary significance of the phenomenology of temporal flow and to what extent is the phenomenology of temporal flow essential for agency.[/quote]
I think I'm up to that explanation, which, from a physicalist point of view, can be explained through entropy and evolution, but almost nobody actually accepts physical monism deep down. I think I have but it was a multi-year struggle to shake off the biases put there by a very proficient liar.
So the story from the dualist POV (there is an (physical or spiritual, doesn't matter) identity 'I' that consistently experiences the life of physical body X. The analogy here is that physics is like a first person Harry Potter movie and the experiencer is the guy in the cinema. Eternalism is the same thing, except no cinema, no entity watching the show, and especially no projector.
Under presentism, the present is whatever frame is currently being projected. Normally the film runs front to back, but if it were run back to front, the experiencer in the cinema would notice the difference but Harry would not. The movie would end with the guy in the cinema knowing Harry's life story (the future) but Harry wouldn't even know that he's a wizard at the end. Harry obviously has different memories than the guy in the cinema. So the movie always runs forward because we'd be able to tell if it didn't.
Hence it being totally unintuitive to such a dualist to conceive of eternalism, which requires the lack of the experiencer (the definer of the present), and he interprets the description (the word 'static') as the experience of a stuck projector. The view is anything but that.
The eternalist view has no experiencer. It doesn't even have Harry (as an identity). It only has the individual frames in the film and one can talk about the experience of that frame, and yes, the experience of any given frame is one of motion of the passing car. One is forced to use B-series language to express what each frame experiences because there is no preferred frame defined by a projector, and A-series requires that preferred reference. By 'frame' here, I'm talking a frame of film (the local state of things at a particular time), and not relativity's reference frame.
The problem that I see here is that there is no inherent connection between the direction of time given by the time coordinate of the relativistic spacetime and the direction of time from the entropy gradient (which in turn is a proxy for physical time). Even if it so happens that in our universe these two never diverge, when you make a commitment to relativistic time, you are opening yourself to this contingency where your theory may diverge from reality.
And in case of heat death, which is currently taken to be the most likely future of our universe, this is more than just a contingency. If the prognosis is right, then eventually relativistic time will diverge from physical time.
So as a proxy for physical time, relativistic time is fine, most of the time, but it should not be taken to be identical with physical time, on pain of paradoxes.
It's been a long time since I studied special relativity (we spent several weeks on it in Physics 101), but IIRC, relativity doesn't provide a forward and reverse direction of time. It just provides two directions of time, and they are symmetric.
Sure, there's talk about the "future" direction and the "past" direction, but it seems to me that that is just so that you can do thought experiments and the like about causality. Those two directions, for the purpose of thought experiments, are specifically chosen to match with thermodynamics. But other than for the purposes of thought experiments involving causality, which presupposes well-behaved thermodynamics, special relativity IIRC is completely agnostic on which direction is the future and which is the past.
|>ouglas
I don't think you understand how philosophy works. You pointed me at something that putatively needs to be explained, and I provided my putative explanation. It is now your job, should you chose to accept it, to provide your putative explanation for why what I argued is wrong.
Instead of doing this, you just repeat the same thing, as if I have said nothing.
Also, you seem to be arguing from authority that Miller is right and consequently I am wrong. This is bad philosophy for several reasons. I'm not going to get into all of the reasons for that, but I will point out that you seem to think that Miller is on your side. At least from this article, she is not. The book from which this chapter was selected seems to be a textbook that a Philosophy professor would assign their students to read. Such treatises are often specifically designed leave certain questions unanswered, in order to allow for debate in the classroom and for students to write papers where they have the leeway to chose which position they want to argue for.
I will point out that Miller also describes plenty of problems for presentists, and you are cherry-picking your argument from authority by ignoring the fact that Miller has more objections against presentism than she has against eternalism. This probably just follows from the fact that the orthodoxy these days is that eternalism is the true account. (I don't know this for sure, but that's the impression that I got from attending some Philosophy conferences at MIT where everybody but me was actually a professional philosopher.)
|>ouglas
P.S. It's likely the case that your actual worry is about phenomenal consciousness. If that's the case, I am quite sympathetic. I am not a physicalist with respect to phenomenal consciousness myself, and I'm sure that feelings similar to mine are one of the reasons for the spotlight theory being prevalent to whatever degree it is, but despite many years pondering and studying the issue of phenomenal consciousness, I feel no closer to an answer today than when I started.
I am only trying to get some acknowledgement from you and others in this discussion that Eternalism entails a static world devoid of any temporal flow, change or motion.
You appear to maintain that the world works the same way whether Presentism or Eternalism is true, but it remains to be explained how anything works if nothing moves. You and others appear to maintain it is unproblematic that we find ourselves now at one time and now at another, or that we find ourselves aging, when according to Eternalism nothing moves from point A to point B (or from time A to time B).
Quoting Douglas Alan
I consider Miller's article to be an even-handed presentation of the issues, and you might recall that it was introduced in the OP, not by me. Call it "argument from authority" if you like, but I am simply attempting to have it recognised that Eternalism entails a motionless world. Many seem to find this either inconsequential or incorrect. This is why I keep returning to the associate professor's article. It can be difficult pushing back against the orthodoxy.
Quoting Douglas Alan
I have never claimed to be arguing for Presentism. I even acknowledged that Presentism has many problems of its own in my first post to this discussion. But it's not all bad.
I think the issue here is that the terms like "motionless" and "static" are ambiguous and emotionally laden when talking about something like eternalism. Let's consider a film reel of the best car chase ever filmed. It's so perfect that no decent aficionado of films could disagree with this.
Now consider that in one sense, this film reel is static. It never changes. In another sense, it's full of change and motion. One can imagine that the film editor working on it, if they were really good, they might not even ever have to watch the scene to edit it. Their sense of film editing might be so refined, that they can just fathom all this motion in their heads from individual frames, while they cut and paste bits of film around.
Now imagine that there might be aliens who love human films. Imagine that they don't need to see the movie projected in real time in order to enjoy our films. They just ask for our films as mp4's and their brains are sophisticated enough to decode the mp4's and model what is going on in a film. And boy do they love this car chase! Even though they have never watched it frame by frame. They just absorbed it all at once. But their brains can model all the exciting motion that is going on the film without having to have actually viewed anything moving.
Or you might imagine the same thing about our greatest novels. All sorts of things might be happening in them, right? But no. Nothing happens in a novel. They are static. They don't change. Well, it depends on what sense of the word "happens" and "change" you are using when use these words to describe the novel.
Again we can imagine aliens, or some super-smart person, who doesn't have to read a novel in order in order to appreciate it. You can give them the pages in any order, and in their heads they can reconstruct the proper order for the pages, and appreciate the entire novel in an instant.
Is a great novel static? Or is it dynamic and full of exciting and interesting events?
You tell me!
Now consider that a human life has some similarities to a novel. If eternalism is true, one can view it as either static, or as very dynamic, depending on what sense of the words you are choosing to use when you describe it.
In any case, even if you just consider the above to be a bunch of incorrent blathering, my account has addressed all of Miller's stated worries about eternalism. I can't go over each sentence at the moment, but let's take just one:
One hugely important reason for this is that we can remember the past and not the future. This is true in eternalism just as much as it is true in presentism. It follows plainly from thermodynamics and information theory.
|>ouglas
You remember right, but that wasn't at issue - we've both acknowledged that this is the case. My point is that relativistic time is not identical to physical time (the time that physical clocks measure). There are at least two reasons to think so: First, it is an idealization that wasn't designed to perfectly track physical time. Second, we have specific examples - probable or at least possible - where relativistic time diverges from physical time.
Why is this important? To bring this back to the original topic, a common argument for the B-theory and against the A-theory is that the theory of relativity, though it may not rule out the A-theory, does not offer any support for it either. The A-theory requires additional assumptions that are not part of SR or GR. The implicit thesis here is that we ought to base our theory of time on the theory of relativity and nothing else. But this thesis is weakened if the identity between relativistic time and physical time is weakened.
Quoting Douglas Alan
Whether a novel or a book or the world is static or dynamic is not the right question. Let's assume that the world is static, as per Eternalism. Then the question becomes: how are we able to perceive it? That is, why do we perceive the world the way we do (dynamically) if it really is static? Furthermore, how do our perceptions and/or our bodies work in those conditions? It would seem to require a complete overhaul of our understanding of human physiology to discard dynamism. This includes if we were to consider our perceptions of motion to be an illusion.
In order to perceive/understand a book or a movie, we must read it or watch it, or have someone describe it, or read a summary of the plot; all of which require dynamism as far as I know. Fanciful examples of aliens outside of time, or in a motionless world, who can perceive books, movies and/or the world simply pushes the problem back a step. It then needs to be explained how the perceptions of those aliens works in a static world.
Quoting Douglas Alan
This begs the question. Why assume that 'time flows' from ordered to disordered states? Because that accords with our perceptions? It remains unexplained why there should be a preferred directionality to our perceptions of temporal flow if nothing really moves.
I don't assume that time flows from ordered to disordered states. In fact, since I have stated that eternalism is true, I have stated that time doesn't flow at all. This doesn't mean that our brains can't represent time as flowing.
You seem to constantly willfully ignore a fact that I have repeatedly stated: SInce physical law is the same under both eternalism and presentism, our brains are going to be in the same states either way for any given point in time. And because they are going to be in the same states either way, our minds are going to represent things the same way regardless of whether it is eternalism that is true or presentism that is true.
The question that needs to be answered it not why does time flow in a certain direction. The question that needs to be answered is why does time seem to flow in a certain direction. The answer to that question is because our brains represent time as flowing in a certain direction whether or not there is actually any flow.
All I have to do is explain why our brains represent things in a certain manner, and then I have answered why things seem to be a certain way. The only way that things can seem to be, is the way in which our minds represent them.
Why does the world seem to be three dimensional, rather than nine dimensional, for instance? The world may be nine dimensional. That is what is predicted by string theory. The short answer is because our minds represent the world as three dimensional. Because our minds represent the world as three dimensional, the world seems to be three dimensional.
Is it your assertion that our brains can represent things as being one way, and yet it could seem to us that things are different from how our brains are representing things? If that's your assertion, I'd certainly like an account of how this is possible and how it would work!
|>ouglas
You implied that time has a naturally preferred directionality when you stated that we remember the past and not the future, which "follows plainly from thermodynamics and information theory." I don't see how you can consistently argue both that time doesn't flow and that time has a preferred directionality.
Quoting Douglas Alan
If nothing moves or flows, then how do we get from one brain state to the next? Are there any theories of how our brains work (e.g. to produce our minds and represent things) which do not require motion?
I have not said that time has a "preferred directionality". I have said that you can remember the past and not the future. Which direction is "preferred"? The directions just have different properties due to the laws of thermodynamics. Laws which are not affected in the slightest by eternalism or presentism.
Repeat after me: FOR EVERY POINT IN TIME, THE PHYSICAL STATE OF THE UNIVERSE AT THAT POINT IN TIME IS IDENTICAL UNDER ETERNALISM AND PRESENTISM.
Until you can acknowledge and comprehend this irrefutable fact, you will be forever lost.
Quoting Luke
Who says that we "get" from one brain state to the next? At time T1, you are in brain state A. At time T2, you are in brain state B. For any given time Tn, physical law tells us what brain state you will be in. And that brain state will be the same brain state whether eternalism is true or presentism is true.
Quoting Luke
Repeat after me: FOR EVERY POINT IN TIME, THE PHYSICAL STATE OF THE UNIVERSE (INCLUDING YOUR BRAIN) AT THAT POINT IN TIME IS IDENTICAL UNDER ETERNALISM AND PRESENTISM.
|>ouglas
Let's just say you implied that time has a direction, or that there is an arrow of time, if you will. How is this consistent with your agreement that "time doesn't flow at all"? No flow should entail no direction.
Quoting SophistiCat
Okay, sorry.
Does space flow towards the north pole? And yet there is a spacial "arrow" that points towards the north pole.
And the state of things that are "here" is different for every point in space that lies between me and the north pole.
In eternalism, "now" is like "here", only for time, rather than for space, and the "past" (the direction towards the Big Bang) is like "south" and the "future" (the direction away from the Big Bang) is like "north".
Now why would any of this commit me to whatever your concept of "flow" is? I have my own notion of "flow", but it only entails that for adjacent points in time, we have some power of calculation about how the physical state of the universe will differ between those two points in time. These powers of calculation come from our understandimg of physical law. And what we will calculate, and what the actual states will be, is unaffected by eternalism vs presentism.
|>ouglas
Personally, I would not refer to time as measured by a clock as "physical time". I would call it "clock time" or some such. Time as measured by a clock is stochastic. It only follows from the second law of thermodynamics, which is not fundamental law. It doesn't even make an assertion that is true in all possible worlds that have the same fundamental law as ours. And that have a Bug Bang.
There is a possible world where my fair coin has always come up heads, even though I have tossed it a quadrillion times. Likewise, there is a possible world in which my pocket watch has always run backwards, without being broken in any way.
In my eyes, "physical time" must not be stochastic. (Unless it turns out that the universe is stochastic all the way down.) Consequently, Relativity provides for two directions of time. This is the only "physical time". There are two directions of physical time that point in opposite directions, and we label one the future and one the past for our convenience. But in perverse situations, and after the heat death of the universe, these labels may not be perfectly appropriate.
The fact that clocks are not reliable in all possible worlds, or after the heat death of the universe leads me to exactly the opposite conclusion: We should not be making any profound metaphysical conclusions at all based on clock time. We should stick to relativistic time. Labeling one direction of time the future and one the past is just a convenience for discussion, in that we are usually talking about situations that have a readily fathomable entropy gradient.
|>ouglas
The second law of thermodynamics gives a preferred overall direction for time, but the rate of time is established by any number of regular physical processes, such as the vibrations of a cesium atom, which are used for the standard atomic clock. It is the availability of such physical processes - plus an overall direction - that gives us time as we normally understand it in physical sciences. (A direction is still necessary to provide an order to the cycles of a physical process - otherwise you can't really say that this cycle occurred earlier or later than that cycle.) We can also talk about subjective psychological time and other kinds of time - these I distinguish from what I call physical time (or clock time, if you prefer). The coordinate time of the Minkowski or the Lorentzian manifold is one of the species of time that, I argue, is not identical to this generalized concept of physical time.
The second law of thermodynamics may not be fundamental, in the sense that it is reducible to physics at a lower scale, but all you need for it to obtain is a non-equilibrium state - and then it becomes as inevitable as any fundamental law. Almost as inevitable. I take your point about it being statistical. But does this strike a blow against the idea that thermodynamics is essential to our understanding of time? I understand probability and statistics epistemically, so if you tell me that the probability of an outcome is 1 - 10[sup]-45[/sup] (that's the probability of a quadrillion coin tosses not all coming up heads), that's probably better than the confidence level of all our fundamental physics experiments combined.
Quoting Douglas Alan
I am with you, to a point: I am not big on metaphysics. I would rather confine myself to more modest phenomenological models.
Note that when you object to thermodynamics playing any part in the definition of time on the grounds that other possible worlds with the same fundamental laws may not exhibit such thermodynamic asymmetry as is observed in our universe, you are already deep into metaphysical theorizing, perhaps without even realizing it.
Actually, you never really defined what you mean by 'relativistic time'. You say physical time is that which clocks measure. I think physics would say that a clock measures proper time, a frame independent property of any timelike worldline. Clocks, not being confined to a single point, cannot be perfect, just like the exact length of a curving road is ambiguous because the road has nonzero width.
I digress. What do you mean by relativistic time? You said the two are usually the same except after heat death, but that doesn't tell me what you mean by the term, especially since a clock cannot exist in heat death conditions. It seems that time in general (both duration and direction) fade to meaninglessness along with most other physical concepts.
Sure. But as you note later, proper time can be well-defined even in the absence of anything to mark its passage, and that is where I see a problem. You could have a relativistic spacetime with nothing else, and formally it would still have time of every description. But would it be physically meaningful?
Of course, here we run into the more general question of the nature of the physical law. Are laws ontologically prior to things and events that are subject to them? Do they describe potentialities (like what would happen if that empty spacetime did have something in it to demonstrate its relativistic properties)? Or do laws serve only to connect the dots, describe the regularities in our observations? In the latter case - and only in the latter case - it would be unjustified to talk about time in the absence of anything that is time-like. I think I lean towards the Humean regularity view.
One might object that clock time, as instantiated by physical clocks (regular processes), is a naive concept and that relativistic time is more fundamental. But clocks are epistemically prior to our concept of time. The reason we came up with the theory of relativity in the first place was to give a better account of clock-based time (among other things). Without clocks what is the point of relativity?
An empty, flat spacetime with a positive cosmological constant is an interesting case. Formally, there is a temporal process (expansion of spacetime), but with nothing clock-like to register the passage of time, does it still make sense to talk about time? Does it even make sense to model it with a Lorentzian manifold and Einstein's field equations?
Quoting SophistiCatNo, time without change is meaningless, as is say motion of an object in the absence of other objects. The words might as well be invisible pink unicorns.
I seem to be in the latter camp. Spacetime with nothing in it doesn't have relativistic properties.
Can there be time without clocks? Surely there are primitive people and animals with an awareness of time, but they also arguably have clocks, however inaccurate. If the speed of light was a lot slower, its properties could be more apparent and intuitive to primitive beings who may not have developed accurate measurements for it yet. Similarly, our intuitive perception of time as flowing is only there because that perception makes us more fit, not because time necessarily flows.
Meaningless. If it has stuff, I don't think it can be flat. If it were, an inertial frame could foliate the space, and it cannot.
Time is an integral part of relativistic spacetime. If you need a specific measurement of time, you can use proper time in conjunction with a specific timelike worldline, or a coordinate time in conjunction with a specific reference frame - doesn't matter, since they are all mutually convertible.
Quoting noAxioms
I mean "clocks" in a general sense, as any observable regular physical process, such as an oscillation.
Yes. Clocks measure time. Put a clock next to an irreversible process (which are all real particle processes) and you can measure how many periods it took. Which always is an approximation, as perfectly periodic motion is reversible and such process doesn't exist, the exception being the motion of virtual particles, being the only presence in the 3D space of the pre-inflationary era, "waiting" to be set in thermodynamic unidirectional motion before the sign is given by two previous 3D universes accelerating away from the 4D circularity.
The time used in relativity is an ideal, reversible clock, of which you can't tell it's going forwards or backwards.
[quote=John8:58]Jesus said to them, “Truly, truly, I say to you, before Abraham was, I am.”[/quote]
The searchlight in the block universe that is everywhere at once, is consciousness, which is nothing other than God's knowledge. But it is surely hubris for ordinary mortals to pretend to this god's eye view. Therefore I am a presentist - it's all "I" can know.
And what or who determines the motion inside the block?
Frankly, your guess is as good as mine!
Get the angle right and we could see T. Rex chasing down a triceratops or, get this, even see the dino-killer asteroid streaking through the sky. 10-9-8-7-6-5-4-3-2-1-0!!! Kaboom! The end of the thunder lizard epoch!