Have you worked out yet how to account for eternalism's lack of motion, or are you still ignoring that eternalism has this problem? — Luke

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?

There is no "lack of motion" in eternalism, so yes I ignore fictitious problems. — Inis

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?

Why do you think there is no motion under eternalism, particularly if that were the case, no one would advocate it? — 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 no "lack of motion" in eternalism, so yes I ignore fictitious problems. — Inis

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.

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. — Luke

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.

Did you not see the quote I posted on the previous page of this discussion:

The resulting timeless cosmos is sometimes called a “block universe” — a static block of space-time in which any flow of time, or passage through it, must presumably be a mental construct or other illusion.

It seems quite clear to me.

The block has both those states, separated by 2 seconds. — noAxioms

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.

It surprises me how advocates of eternalism presume the right to the only redeeming aspect of presentism.

Did you not see the quote I posted on the previous page of this discussion:

The resulting timeless cosmos is sometimes called a “block universe” — a static block of space-time in which any flow of time, or passage through it, must presumably be a mental construct or other illusion.

It seems quite clear to me. — Luke

Yes. That quote does not say there is no motion or no time. It just says time doesn't flow in that model.

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. — Metaphysician Undercover

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....

Idk about anything,, but time travel isn't possible lol.

Yes. That quote does not say there is no motion or no time. It just says time doesn't flow in that model. — noAxioms

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"?

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 — Luke

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.

Ditto with presentism, which also has states in between, else it is a series of discreet jumps. — noAxioms

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.

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.... — 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.

The question of whether closed time-like curves exist in our universe is still open, — Inis

That would have to involve reifying time in an odd way (that's completely without justification in my view).

So, physicists are really studying time-travel into the past. A-theory says they are wasting their time. They aren't. — 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.

That would have to involve reifying time in an odd way (that's completely without justification in my view). — Terrapin Station

I'm puzzled why an expert general relativist like yourself wastes your time on this forum rather than publishing your views in Nature.

Why does the article say that the flow of time, or passage through space-time, "must presumably be a mental construct or other illusion"? — Luke

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.

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. — SophistiCat

Nope. Presentism is falsified by several well known experiments, including time-dilation, twin paradox, and the fact that your GPS actually works.

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. — SophistiCat

Nope. Presentism is falsified by several well known experiments, including time-dilation, twin paradox, and the fact that your GPS actually works. — Inis

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.

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). — prothero

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...)

Nope. Presentism is falsified by several well known experiments, including time-dilation, twin paradox, and the fact that your GPS actually works. — Inis

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.

You seem to be interpreting presentism as a denial of relativity. But I haven't seen anyone claim that. I certainly don't. — Andrew M

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.

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. — SophistiCat

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)?

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. — Inis

Your present is not necessarily 'the present'. In fact, quite unlikely to be. Presentism is safe from this sort of argument in my opinion.

Your present is not necessarily 'the present'. In fact, quite unlikely to be. Presentism is safe from this sort of argument in my opinion. — noAxioms

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.

I still don't understand. If presentism posits a passage of time while eternalism does not, then how is motion possible according to eternalism? — Luke

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.

Why is it referred to as a static block universe? — 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.

And the illusion?

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. — 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?

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. — SophistiCat

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.

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. — 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".

@ Luke, Please note that I don't intend to argue that eternalism is true, only that the reductio ad absurdum style argument you make does not succeed. Indeed, it may even be the case that eternalism is false, but not for the argument from experience that you make.

eternalists still need to account for the appearance or illusion of passage. How can time appear to pass if no time actually passes? — 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

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...) — SophistiCat

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.