Relativity?

[Noax]

Wherein it is argued, persuasively as far as I can see, that relativity entails that all objects (including humans of course) actually exist at all times and not just at what we call the indexical "present" time. Past and future are ontologically real along with the present.

I think the block universe model says that all events exist equally, but not that a particular ontological state is or is not. So the opposing view is that some subset of events have a special ontological status, despite the fact that it makes no empirical difference.
I protest Minkowski's framing of his argument as a 'proof' since the 4D model is not one of ontology. Yes, the model is 4D, and thus it is pretty inconsistent to adopt an actual view of reality that doesn't match the only model that works. But even if the alternative is to posit invisible undetectable unicorns, the argument does not prove their nonexistence, just demonstrates the pointlessness of asserting what cannot be detected. It's why I wont take a stance of 'knowing' that the undetectable unicorns don't exist.

[Noax]

I gather that experiments could not exist unless worldlines intersected. That worldlines intersect is a function of time as well as of position, direction, and mass.

Worldlines are a feature of the 4D model and don't have meaning in the 3D one. But experiments are a meaningful concept in the 3D model so worldlines are not why 4D is necessary.

I had a hard time following the rest of the post.

[Belinda]

I gather that experiments could not exist unless worldlines intersected. That worldlines intersect is a function of time as well as of position, direction, and mass.

Worldlines are a feature of the 4D model and don't have meaning in the 3D one. But experiments are a meaningful concept in the 3D model so worldlines are not why 4D is necessary.

I had a hard time following the rest of the post.

Noax, do you at least understand me when I say that existence is mind-independent? You may object that mathematics exists ontologically not, as I would have it, that mathematics exists only as a mental model of reality.

Do you also understand that Descartes, who claimed that he proved that he existed by reason of his thinking, was right in his method of doubt but was in error only by his presuming that there must be a subject of thought ? That's to say that Descartes rightly proved that there was thinking going on, but he did not prove that it was Descartes who was doing the thinking. The fact of thinking is not the same as the fact that there is a thinker of thoughts. By the same reasoning that existence is the case is not the same as that any mode of existence is the case. It follows that the existence of things is mind-dependent, but that existence itself is independent of thinkers.

Past, present, and future are mind-dependent categories, as are the categories of mathematics.

Can you tell me why you think that experiments make sense without the dimension of time? I would have thought that if an experiment E is taking place without the dimension of time then experiment E is disregarding relativity pro tem of the experiment.

[Noax]

Noax, do you at least understand me when I say that existence is mind-independent?

I cannot be sure what you personally might mean by that, but on the surface, it seems to be an ordinary assertion of idealism of a kind. The 3D model of the universe is an idealistic model of time, but a realist model of space. Since spacetime is demonstrated to be one thing, this seems to be a inconsistent view to take, hence Minkowski declaring it provably wrong.
Descartes did not conclude idealism. He did not say that is thinking was what produced his existence, merely that it was evidence of it. He also was working on a much thinner set of scientific knowledge, some recent finding of which cast some of his assumptions (he tried not to have any) into definite doubt.

You may object that mathematics exists ontologically not, as I would have it, that mathematics exists only as a mental model of reality.

My stance is that it doesn't matter. Number and mathematics might exist to say a platonist, and not to you, but both sides agree that 2+2=4. It seems that mathematics works either way and is not existence dependent, except in the sense of existential quantification (a term of which I recently became aware). So the physicists say that a given subatomic particle is not really there, and reduces to pure mathematics. That mathematics works (I think) whether or not the mathematics exists (I am), so 'I am' doesn't follow. That mathematics is not being performed by a mind, but rather the mind being performed by it (says the non-idealist), so it seems that if numbers don't exist, then neither do we since that's what we're apparently made of.
Anyway, that's sort of how I've worked it out. Not putting this out there in a persuasive sense that this is the correct view.

Do you also understand that Descartes, who claimed that he proved that he existed by reason of his thinking, was right in his method of doubt but was in error only by his presuming that there must be a subject of thought ? That's to say that Descartes rightly proved that there was thinking going on, but he did not prove that it was Descartes who was doing the thinking.

"I think therefore" seems to say that there is a thinker, but that is an English translation and I'm not sure it is a good representation of his deductions. He was aware of doubt, and he worked up from that. Doubter came later.
You talked about personal identity, and it is relevant here. Thinking is a process, but doubt is a state, I can have doubt, but to doubt (not just have it) is thought, which is a process, a change in state between me and some past state that is not identical to me. So I only remember thought, but don't perform it.

The fact of thinking is not the same as the fact that there is a thinker of thoughts. By the same reasoning that existence is the case is not the same as that any mode of existence is the case. It follows that the existence of things is mind-dependent, but that existence itself is independent of thinkers.

This part I still didn't follow, and I nearly agree with it, but probably not in the same way. The existence of things (the moon say), what we label as the moon (naive realist view), is arguably observer, language, or mind dependent, but the thing-in-itself, which may not even be named, seems not observer/mind dependent. The moon did not beging to exist because humans arrived on the scene, it just wasn't 'the moon' then.

Can you tell me why you think that experiments make sense without the dimension of time? I would have thought that if an experiment E is taking place without the dimension of time then experiment E is disregarding relativity pro tem of the experiment.

I want to test the water temperature. A moment later I put my hand in water, and a moment later, I realize the water is cold. That is an experiment done in a 3-D model. It is something that happens. It was a valid thing to do. It's how most things are still framed today. Nowhere in that test was a dimension of time required. It can be framed as a series of steps that just happen. Relativistic experiments are not necessarily able to be framed that way, as illustrated by ken who is attempting to do just that.

[surreptitious57]

A moment later I put my hand in water and a moment later I realize the water is cold

Nowhere in that test was a dimension of time required

So did no time at all pass between those two moments

Assuming time was frozen or did not exist could that experiment still be conducted

[davidm]

]I want to test the water temperature. A moment later I put my hand in water, and a moment later, I realize the water is cold. That is an experiment done in a 3-D model. It is something that happens. It was a valid thing to do. It's how most things are still framed today. Nowhere in that test was a dimension of time required. It can be framed as a series of steps that just happen. Relativistic experiments are not necessarily able to be framed that way, as illustrated by ken who is attempting to do just that.

Well, of course, a dimension of time was required, as you yourself noted: "A moment later..."

I should note that it is not Minkowski insisting on the literal 4D world, but Petkov, explicating, persuasively as I think, Minkowski's work.

Try to imagine Einstein's original train thought experiment in a 3D as opposed to a 4D world. I can't.

[davidm]

Look at Einstein’s original train thought experiment.

An observer sits on a train equidistant between the front and back of the moving train.

An observer is on the ground.

When the train moves in such a way that the observer on the train and the observer on the ground are able to look at each other in the the eye, lightning flashes go off.

For the ground observer, the lightning strikes the front and back of the train simultaneously.

For the train observer, the lighting hits the front of the train first, and the back later.

This means there is no universal quantification, only existential quantification in differing planes of simultaneity. The two observers have different presents.

The key point is that for the train observer, even though she does not know it, the future is set in stone. There will be a lightning flash at the rear of the train, sometime soon in her future. This is guaranteed by the fact that the rear train flash already occurred for the ground observer.

Conclusion: the future exists, along with the present and past.

[Noax]

Well, of course, a dimension of time was required, as you yourself noted: "A moment later..."

A moment later I put my hand in water and a moment later I realize the water is cold

Nowhere in that test was a dimension of time required

So did no time at all pass between those two moments

The 3D model has time passing between the two moments. The 4D model has time as a dimension, not something that passes.

Assuming time was frozen or did not exist could that experiment still be conducted

I suppose the 4D model might describe time as 'frozen', meaning it doesn't flow.

I should note that it is not Minkowski insisting on the literal 4D world, but Petkov, explicating, persuasively as I think, Minkowski's work.

OK, this makes some sense. Minkowski was initially working from a flat model, not one with relativity initially built in. Relativity made it more of a requirement.

Try to imagine Einstein's original train thought experiment in a 3D as opposed to a 4D world. I can't.

I can, but at most one of the inertial frames can be the correct one, and the entire experiment must be conveyed from that frame. Light speed is not constant, but the moving observer can't tell because his clock is not accurately measuring time.

[Noax]

Look at Einstein’s original train thought experiment.

An observer sits on a train equidistant between the front and back of the moving train.

You presume the train is moving. You presume a lot of things in fact.

An observer is on the ground.

When the train moves in such a way that the observer on the train and the observer on the ground are able to look at each other in the the eye, lightning flashes go off.

This last statement (and some below) presumes a simultaneity that has not yet been established. The two flashes go off, but the two events being simultaneous or where the observers are is unknown. Your description presumes relativity to already be true. Given what we know, I suppose we can do that, but it isn't the original thought experiment then.

For the ground observer, the lightning strikes the front and back of the train simultaneously.

For the train observer, the lighting hits the front of the train first, and the back later.

This means there is no universal quantification, only existential quantification in differing planes of simultaneity. The two observers have different presents.

Only if described in the 4D model. The 3D one still works, but your description here and below begs the 4D one.

The key point is that for the train observer, even though she does not know it, the future is set in stone. There will be a lightning flash at the rear of the train, sometime soon in her future. This is guaranteed by the fact that the rear train flash already occurred for the ground observer.

Conclusion: the future exists, along with the present and past.

So let's assume the 3D model.

An observer sits on a stationary train equidistant between the front and back of the train. (I have arbitrarily selected the train frame as the correct one)

An observer is on the moving ground.
Lightning flashes go off, hitting the front of the train first, and the back later, and also leaving marks on the ground.
The train observer is midway between the two events, and records the front strike first. Being equal distant from the two events, the observer knows the front strike happens first.

The ground observer is moving towards the rear of the train, and by the time the light from the two signals meet, he is at the point where they meet, so he measures the two signals as arriving simultaneously, but one has traveled further than the other, so this is expected. His clock also runs slow, but since he didn't use it, nobody cares.

I think that sort of covers the case. It assumes absolute time and space (separate, not 4D spacetime), and it still works.
I'm not arguing against the universe being 4D, just against this 'proof' that 3D cannot be. I did an advocatus diaboli piece on presentism vs. relativity. It is still considered an interpretation, lacking an empirical difference.

[davidm]

More on this subject from Petkov (I don’t think I’ve linked this before): Relativity, Dimensionality and Existence

Noax, I’m not sure how your analysis changes anything. We can forget all about motion and just note that there are two observers, each of whom counts herself as stationary and their clocks tick normally for them.

For observer one, the present moment consists of a lightning flash. Some time passes, and then at a later moment that the observer will later call “the present” a second lightning flash occurs.

For observer two, both lighting flashes occur at the same present moment.

Presentism is that thesis that all events and objects exist simultaneously — in the present. The past used to exist but it no longer does; the future does not yet exist.

Yet here we have a clear ontic as opposed to epistemic counterexample to presentism. According to observer one, if she is a presentist, the future does not exist. Yet clearly from the standpoint of observer two, what observer one calls the “future” does exist — it exists for observer one, because for observer one, the two flashes happen at the same time.

One would have to show how this state of affairs is consistent with presentism. A priori it seems it cannot be, but I’m not dogmatic on this point and would like to hear a good argument for presentism, which in fact I am looking for. I have found a couple of rebuttal papers to Petkov that I have not read yet, and I know that William Lane Craig has vigorously defended presentism.

For the eternalist, the situation described above is entirely unproblematic. Since the world exists as a 4D whole, the different planes of simultaneity are simply two different 3D cross sections of an existent 4D world, rather like a loaf of bread that is carved at two different angles by two people wielding different knives.

Relativity can be formulated in either 3D or 4D terms. But this is epistemic, and if we consider the matter from an ontological point of view, the world cannot be both 3D and 4D, can it? It must be one or the other. Would you disagree? Or would you consider the point somehow moot since equivalent descriptions that yield the same result are both fine? It sounds like saying that the Ptolemaic description is fine, which it is from an epistemic standpoint, but surely it’s actually true, contra Ptolemy, that the earth and sun revolve around a common center of gravity close to the sun?

[davidm]

Your description presumes relativity to already be true.

Well I don't think I exactly presume this, but hold relativity to be correct based on evidence. Of course if relativity is actually wrong then the whole discussion is moot.

[Noax]

Your description presumes relativity to already be true.

Well I don't think I exactly presume this, but hold relativity to be correct based on evidence. Of course if relativity is actually wrong then the whole discussion is moot.

With Einstein's original thought experiment, relativity was a conclusion, not a premise. That's what I meant with my comment you quoted above since you framed your description as paralleling that thought experiment.

But (as the context you removed said), we're not trying to demonstrate relativity here. That has pretty much been established. We're discussing the proof against the 3D model vs. the 4D spacetime one, a difference only of ontology. So for that, it is fine to presume relativity, but presuming 4D is not allowed in disproving 3D. To do so would be begging. I tried to point out a few places where that seemed to occur.

So I assumed relativity and a 3D space, and absolute time that flows, and tried to describe the same scenario in those terms. Other than the complete lack of a way to measure this absolute time (no empirical difference between the views), the experiment can be performed. I think the linked article claimed otherwise, and I protest that claim.
Perhaps I am misrepresenting the 3D model that they've 'disproved'. The one I am using is trivially derived from the 4D model with the addition of two (both undetectable) elements: An objective foliation of spacetime (General relativity actually suggests one), and then presentism: the collapse of the one now-objective temporal dimension, leaving the universe as only space, all of which exists simultaniously. The universe now 'happens' instead of 'is'. The addition of these two things is no change to the 4D model except a designation of special ontological status to a subset of events. There can be no empirical difference to that, and thus no proof that one model is wrong.

[davidm]

Noax, I’m having a hard time making out some/most of your above post. I freely admit this failure might be due to my limited (perhaps reparable?) comprehension.

I agree that in Einstein’s original thought experiment, relativity was a conclusion and not a premise. I don’t see why you think I said otherwise. Einstein’s only premises, or postulates, were that the laws of physics were the same in all inertial frames and that the measured speed of light was constant in all inertial frames. From this relativity theory followed, but was not presupposed. Perhaps I misunderstand why you think I said otherwise? Or perhaps I misunderstand what you are claiming that I claimed.

In any event, relativity theory, whether actually true or false, is held to true arguendo for the purpose of the presentist/eternalist debate. This is perfectly valid from a philosophical standpoint.

I see you charge me with leaving out some unspecified context. This implies deliberate intent to leave out a context in order to “win” an argument, which is not at all what I’m trying to do. Perhaps again I misunderstand your point. I can only say that I never intended to leave out any context of a statement of yours, but may have done so out of ignorance or lack of understanding of what you were arguing for.

How is presuming 4D not allowed in disproving 3D? Is there a third (or more) alternative, if 3D can be disproved?

But maybe this involves the rest. You say you posit an admittedly undetectable absolute flow of time and then two other undetectable elements, an objective foliation of spacetime followed by presentism. Have I understood? If I have understood, then what you are suggesting is that the search for the objective truth about the world is futile, and I can’t necessarily disagree.

Again, I may have misunderstood your post (sincerely misunderstood and not deliberately leaving out context!) but maybe what you are arguing for is theory undetermination, which is fine. However, if that is what you are arguing for, it is not clear to me.

[davidm]

Also, with respect to your interpretation of Einstein's train thought experiment, I'm not sure how or why you are saying (if you are saying) that this differs from the standard interpretation?

[Noax]

Noax, I’m having a hard time making out some/most of your above post. I freely admit this failure might be due to my limited (perhaps reparable?) comprehension.

Short on time right now, but I'll try to clarify, only briefly in this post.

In any event, relativity theory, whether actually true or false, is held to true arguendo for the purpose of the presentist/eternalist debate. This is perfectly valid from a philosophical standpoint.

Agree, and I tried (and failed) to convey that above.

I see you charge me with leaving out some unspecified context. This implies deliberate intent to leave out a context in order to “win” an argument, which is not at all what I’m trying to do.

No such intent. Just that the answer to your questions were in the post you quoted, but you didn't include them. I'm fine with a presumption of relativity for our purpose.

How is presuming 4D not allowed in disproving 3D? Is there a third (or more) alternative, if 3D can be disproved?

Premise: The universe is 4D.
3D is not 4D, therefore 3D is wrong. This is begging the argument. So we don't use 4D terms or facts to disprove 3D.

But maybe this involves the rest. You say you posit an admittedly undetectable absolute flow of time and then two other undetectable elements, an objective foliation of spacetime followed by presentism. Have I understood?

Presentism IS the absolute flow of time, so just two things, not three.

If I have understood, then what you are suggesting is that the search for the objective truth about the world is futile, and I can’t necessarily disagree.

The article claimed a proof against this, so I've been pushing back. I liked your link, but I don't think it went so far as to claim a proof, but it did claim that it was a fundamental issue, not a non-issue. I expect a 3D view from a layman, but I think it is pretty pathetic that physicists understand spacetime but don't actually think it is a thing.