B Any plausible explanation for dynamical length contraction?

[alexandrinushka]

TL;DR Summary

If one decides to adopt a neo-lorentzian point of view, aren't they at risk of committing to a dynamical length contraction, whose explanation has no room in modern Physics? Otherwise, what such (speculative) explanation might consist of?

I am new here, so pardon my ignorance.

First of all, I am aware of the impossibility to distinguish experimentally between SR (Special Relativity) and LET (Lorentz Ether Theory). I know there is a PF policy article on LET and the Block Universe.

I must admit though that LET is more appealing to me (for reasons of psychological and philosophical nature, mainly because I find it hard to fit our experience in a perdurantist views and because an "open future" is valuable to me as to the thinking creature I am; hope these lines can find some sympathy in the minds of hard-core physicalists).

That being said, I do not feel comfortable embracing ad hoc statements and the Lorentz-FitzGerald contraction, when viewed as a dynamical effect on a rod, moving with respect to preferred reference frame, sounds as ad hoc as it can get...
If I have understood things correctly, time dilation can somehow be described in a Larmor style by referring to the longer path a photon in an Einstein clock might need when traveling in a moving clock. Yet it does not seem to me one can employ the same reasoning when it comes to length. In other words, a true "shortening" of objects in the direction of movement is needed in order to supply LET with the tools needed to match the elegant predictions SR makes.

So, after this long introduction, does a dynamical length contraction contradict any current physical law? Is there anything that makes it impossible? If we consider an electron as some sort of a "wavy structure" with probabilities (yes, I know is the probability that is oscillating and that nothing is actually waving around there) to find it at a certain place around the nucleus, doesn't it seem a bit absurd to imagine this probability squeezed in the direction of motion to match experimental evidence? I do understand this is quite speculative and that we do not have all the answers yet (some would argue we might never have them), I am just not willing to commit to anything absurd and supposedly we may judge a theory absurd or dismiss it even with partial knowledge.

TLDR; are there any reasonable ways to picture dynamical Length Contraction, given the current knowledge we have gained in Quantum Mechanics, without it been too ad hoc?

Edit: I have added an explanation for some of the acronyms.

 

[anuttarasammyak]

I know SR is special relativity and QM is quantum mechanics but do not know LET. Could you teach me what it is?

 

[alexandrinushka]

Sorry @anuttarasammyak, I should have been more explicit:
LET = Lorentz Ether Theory
I'll add an explanation in my original post.
Just for the record, we are not talking about the originally meant ether, but about a framework in which time dilation would be an effect of slowing clocks and length contraction an absolute effect in moving frames. The speed of light in one direction would be c only in a special absolute reference.

 

[Dale]

In other words, a true "shortening" of objects in the direction of movement is needed in order to supply LET with the tools needed to match the elegant predictions SR makes.

Yes, that is true. That is exactly the Lorentzian understanding of the null result of the Michelson Morely experiment.

So, after this long introduction, does a dynamical length contraction contradict any current physical law? Is there anything that makes it impossible?

I am not sure. What is the difference you are intending to draw between a "dynamical length contraction" and simply "length contraction"?

 

[alexandrinushka]

Yes, that is true. That is exactly the Lorentzian understanding of the null result of the Michelson Morely experiment.

Just for the record, I do not hold a degree in Math or Physics, but I do understand the addition of velocities, what a differential and integral is and why one uses matrices.

Also, I do understand the implications of relative simultaneity and their elegant explanation of time dilation and length contraction as their result. So I would only ask in a humble way, probably as an exercise of imagination and a venture into alternative hypothesis, whether such a physical contraction of moving objects (with respect to an absolute frame and proportional to the speed of the moving frame compared to the latter frame) would make any sense, even in a wild speculative way. As I have mentioned in my original post, I do not want to commit to absurd metaphysics and imagining the wavy nature of particles changing their probability distribution depending on speed sounds um... ad hoc.

 

[alexandrinushka]

What is the difference you are intending to draw between a "dynamical length contraction" and simply "length contraction"?

Oh... By dynamical length contraction I mean the object really shortens as it moves compared to an absolute frame. By length contraction I mean the apparent effect in SR, when actually nothing contracts at all, no squeezing is happening, it's just a kinematic effect of measuring a length in another frame with local rulers and clocks.

 

[Dale]

By dynamical length contraction I mean the object really shortens as it moves compared to an absolute frame.

Then yes, a dynamical length contraction does contradict current physical law which states that there is no absolute frame.

 

[alexandrinushka]

Then yes, a dynamical length contraction does contradict current physical law which states that there is no absolute frame.

Doesn't it rather say that positing an otherwise indetectable frame is superfluous and rubs the Occam's rasor in the wrong direction?

 

[PeterDonis]

because an "open future" is valuable to me

This appears to imply that you believe standard SR is inconsistent with "an open future". Why do you think that?

 

[alexandrinushka]

This appears to imply that you believe standard SR is inconsistent with "an open future". Why do you think that?

Yes, I do believe that on a standard reading SR is incompatible with an open future. I find Putnam's argument and the Andromeda paradox compelling in this regard.
I know it's not a philosophy forum so I am afraid I'd irritate readers and go against the PF policy by going into too much detail, but I am convinced that a standard reading of SR implies that all the moments of our lives, past, present, future, co-exist (time would be akin to a spatial dimension, where all the moments of our lives and the universe would lie next to each other as on a movie film).

 

[Dale]

Doesn't it rather say that positing an otherwise indetectable frame is superfluous and rubs the Occam's rasor in the wrong direction?

Well, this is a bit of semantics. The distinction between physical laws and physical theories is not set in stone. But in my opinion physical laws are not theories, they are the distillation of observed facts. The observations are that there is no absolute frame. Hence, the physical law is that there is no absolute frame.

You can make a theory which says that there is an absolute frame and proposes some scheme to hide the violation of the law from measurements, but the law itself is that there is no absolute frame. Since such a theory has an element which violates the observations, which are the law, then the theory must posit some conspiratorial observational effect. But that is the theory trying to deal with the law, not the law itself.

 

[PeterDonis]

I do believe that on a standard reading SR is incompatible with an open future. I find Putnam's argument and the Andromeda paradox compelling in this regard.

Then you should read this Insights article (the link is to the PF comment thread, which in turn links to the article, but you might want to read the comments as well), which refutes the argument you refer to:

https://www.physicsforums.com/threads/the-block-universe-refuting-a-common-argument-comments.843000/

The short version is that, while the "block universe" interpretation is of course consistent with SR, it is not required by SR.

 

[Dale]

I do not want to commit to absurd metaphysics and imagining the wavy nature of particles changing their probability distribution depending on speed sounds um... ad hoc.

I am afraid that there is no way out, then. The aether of LET is purely ad hoc. The only purpose of the LET aether is to reconcile the observations with the concept of an aether. It serves no other purpose. That is essentially the definition of ad hoc.

It is even worse than usually expressed. The aether is a luminiferous aether, meaning that it is the medium for light. So if the aether is what causes time dilation for a light clock, the electromagnetic force, then there is no obvious reason that time dilation should also occur for the weak force, the strong force, or gravity. What mechanism could affect the EM force, the weak force, the strong force, and gravity all the same? If you posit one single thing that affects them all the same, then in what way does that differ from spacetime? If you posit different things that affect each, then why are all of the effects quantitatively the same? Each of those follow-on explanations for the other forces introduce more ad hoc explanations.

 

[alexandrinushka]

Well, this is a bit of semantics. The distinction between physical laws and physical theories is not set in stone. But in my opinion physical laws are not theories, they are the distillation of observed facts. The observations are that there is no absolute frame. Hence, the physical law is that there is no absolute frame.

You can make a theory which says that there is an absolute frame and proposes some scheme to hide the violation of the law from measurements, but the law itself is that there is no absolute frame.

Oh, I see. I think I agree with you here.
We both agree the laws of nature (EM and classical mechanics) are Lorentz invariant. You are saying this is a deep ontological law. I am wondering whether it is just epistemic...

That being put aside, can you help me with my initial question? Just matter-of-factly. Sorry for insisting. I'll try to reformulate it: is the existence of a universal field (or whatever other entity) that would modify the wave function and the probabilities to find the electron in a certain place (by somehow making the probabilities "squeeze" in the direction of motion) unphysical?
Thank you.

I am afraid that there is no way out, then. The aether of LET is purely ad hoc. The only purpose of the LET aether is to reconcile the observations with the concept of an aether. It serves no other purpose. That is essentially the definition of ad hoc.

It is even worse than usually expressed. The aether is a luminiferous aether, meaning that it is the medium for light. So if the aether is what causes time dilation for a light clock, the electromagnetic force, then there is no obvious reason that time dilation should also occur for the weak force, the strong force, or gravity. What mechanism could affect the EM force, the weak force, the strong force, and gravity all the same? If you posit one single thing that affects them all the same, then in what way does that differ from spacetime? If you posit different things that affect each, then why are all of the effects quantitatively the same? Each of those follow-on explanations for the other forces introduce more ad hoc explanations.

I see and I understand why it is ad hoc indeed. I need to ponder upon it.

 

[alexandrinushka]

Then you should read this Insights article (the link is to the PF comment thread, which in turn links to the article, but you might want to read the comments as well), which refutes the argument you refer to:

https://www.physicsforums.com/threads/the-block-universe-refuting-a-common-argument-comments.843000/

The short version is that, while the "block universe" interpretation is of course consistent with SR, it is not required by SR.

Thanks a lot. I'll check it out.

 

[Dale]

You are saying this is a deep ontological law. I am wondering whether it is just epistemic.

I have no idea what a "deep ontological law" is. I just say it is a "law" in the meaning I gave above. If you feel the need to categorize it further for some obscure philosophical purpose, please don't ask me about it. I don't want to be involved in making any philosophical assertions that are outside of my expertise.

can you help me with my initial question?

I thought I already did. I don't see that the reformulation changes anything. You have just kind of changed "violate law" with "unphysical". But since laws are about observations and physics is an observational science, I don't see that the change in wording changes anything substantive.

There is no observational purpose for the LET aether. It is purely ad hoc. If you wish to introduce such a purely ad hoc entity for your philosophical comfort, then by all means do so. But simply do so recognizing that there is no non-ad-hoc justification. There is no observation which it explains and no other purpose for it.

 

[alexandrinushka]

There is no observational purpose for the LET aether. It is purely ad hoc. If you wish to introduce such a purely ad hoc entity for your philosophical comfort, then by all means do so. But simply do so recognizing that there is no non-ad-hoc justification. There is no observation which it explains and no other purpose for it.

Well, um, maybe it fits better with some versions of QM interpretations? Like Bohmian mechanics or a GRW interpretation?
Don't beat me up for this, I've read about the possibility of putting back on the table a "preferred frame" here http://www.scholarpedia.org/article/Bell's_theorem#Non-locality_and_relativity

 

[Dale]

Well, um, maybe it fits better with some versions of QM interpretations? Like Bohmian mechanics or a GRW interpretation?

Maybe, I don't know enough about QM interpretations to say. You should ask about QM interpretations in the QM interpretations sub-section. They are off-topic pretty much everywhere else since the whole interpretations thing is basically philosophical.

Here is the link: https://www.physicsforums.com/forums/quantum-interpretations-and-foundations.292/

 

[alexandrinushka]

It is even worse than usually expressed. The aether is a luminiferous aether, meaning that it is the medium for light. So if the aether is what causes time dilation for a light clock, the electromagnetic force, then there is no obvious reason that time dilation should also occur for the weak force, the strong force, or gravity. What mechanism could affect the EM force, the weak force, the strong force, and gravity all the same? If you posit one single thing that affects them all the same, then in what way does that differ from spacetime? If you posit different things that affect each, then why are all of the effects quantitatively the same? Each of those follow-on explanations for the other forces introduce more ad hoc explanations.

I do not think that aether causes time dilation for a light clock, actually. I was only asking for length contractions.
If one has a certain frame and the light moves with speed c in that frame and then you move a clock with respect to this frame, then light would travel a longer path to bounce between the mirrors of the clock. Clocks would therefore slow down in any other frame. I don't know if one could say that the aether (or whatever other entity) caused it. It just that light just minded its own life in this absolute frame. Again, pardon my ignorance. My field is Linguistics, not Physics, I might be unable to grasp the difficulty of the issue at hand.

And I was not aware of the complications with the weak, strong and gravitational forces. For gravity, I thought it travels with speed c. For the weak force, as far as I know, the speed is difficult to determine due to its short range of action. For the strong force I simply don't know. But again, you might be right and I could not imagine it is that bad.

 

[Dale]

If one has a certain frame and the light moves with speed c in that frame and then you move a clock with respect to this frame, then light would travel a longer path to bounce between the mirrors of the clock. Clocks would therefore slow down in any other frame.

This doesn't follow at all. In that other frame there is no reason for light to move at c and therefore no implication that the longer path implies time dilation.

 

[PAllen]

Then yes, a dynamical length contraction does contradict current physical law which states that there is no absolute frame.

Well, if existence of an undetectable absolute frame is interpretation, not physical law, then, by definition, physical law does not contradict the existence of an undetectable absolute frame.

Also, literature on the the LET interpretation shows how via the EM field of moving charges, there are dynamical interpretations of length contraction. This is, in fact, required by the normal SR interpretation - there must be a physical explanation of length contraction of a body moving in any arbitrary frame compared to one at rest in that frame. The configuration of atoms is different, and this must be consistent with physical law.

 

[Dale]

via the EM field of moving charges, there are dynamical interpretations of length contraction.

That is why I asked for clarification of what the OP meant by "dynamical". What you describe is not the way they were using the term.

 

[PeroK]

Yes, I do believe that on a standard reading SR is incompatible with an open future. I find Putnam's argument and the Andromeda paradox compelling in this regard.
I know it's not a philosophy forum so I am afraid I'd irritate readers and go against the PF policy by going into too much detail, but I am convinced that a standard reading of SR implies that all the moments of our lives, past, present, future, co-exist (time would be akin to a spatial dimension, where all the moments of our lives and the universe would lie next to each other as on a movie film).

I'd be quite blunt and say that most of the philosophical opposition to modern physics is from philosophers who don't understand it. It's sad in a way that something that a reasonably competent undergraduate can master in a few months eludes some influential philosopher, who then builds an alternative edifice whose foundations are effectively an undergraduate error!

The Andromeda paradox is, again to put it bluntly, pretty pathetic; based as it is on a simple inability to grasp that any universal "now" is purely a convention and has no physical significance. Putnam raises a common undergraduate stumbling block to the status of philosophical opposition to modern physics.

Meanwhile, physics moves on; GR follows SR; QFT unifies SR and QM; and, the search for a theory of quantum gravity goes on. The philosophical opposition to this adds nothing to the development of modern science. And, no matter how many long words you weave into a sentence, the result remains free of any scientific significance.

 

[alexandrinushka]

The Andromeda paradox is, again to put it bluntly, pretty pathetic; based as it is on a simple inability to grasp that any universal "now" is purely a convention and has no physical significance. Putnam raises a common undergraduate stumbling block to the status of philosophical opposition to modern physics.

I don't see how using words like "pathetic" undermines Putnam's argument at all. You may not like it, but Putnam (and Penrose, a brilliant mathematician) were quite aware of the lack of a universal "now" in SR and, mind you, so am I. Hence the Andromeda conundrum. Truly I do not see how you or any other author may debunk Putnam's logic otherwise than adopting a Block Universe or a solipsistic view of time.

 

[PeterDonis]

I don't see how using words like "pathetic" undermines Putnam's argument at all. You may not like it, but Putnam (and Penrose, a brilliant mathematician) were quite aware of the lack of a universal "now" in SR and, mind you, so am I. Hence the Andromeda conundrum. Truly I do not see how you or any other author may debunk Putnam's logic otherwise than adopting a Block Universe or a solipsistic view of time.

Please go read the Insights article I linked to. I avoided loaded words in the article, but I agree with @PeroK that the error the argument makes is pretty simplistic. Even brilliant people can make simplistic mistakes.

 

[PAllen]

I don't see how using words like "pathetic" undermines Putnam's argument at all. You may not like it, but Putnam (and Penrose, a brilliant mathematician) were quite aware of the lack of a universal "now" in SR and, mind you, so am I. Hence the Andromeda conundrum. Truly I do not see how you or any other author may debunk Putnam's logic otherwise than adopting a Block Universe or a solipsistic view of time.

The issue isn’t the non existence of a global now, it is the non existence of any notion of “now” that has any physical significance, rather than being purely a convention. Without attaching unwarranted significance to “now at distance” the Andromeda “paradox” collapses to nothing.

Note, all observers agree on what is causal future, causal past, and neither (spacelike relationship in SR). These are the only categories that have any physical meaning. Since all agree on these, you cannot even state the purported paradox in terms of physically meaningful variables.

 

[PeroK]

I don't see how using words like "pathetic" undermines Putnam's argument at all. You may not like it, but Putnam (and Penrose, a brilliant mathematician) were quite aware of the lack of a universal "now" in SR and, mind you, so am I. Hence the Andromeda conundrum. Truly I do not see how you or any other author may debunk Putnam's logic otherwise than adopting a Block Universe or a solipsistic view of time.

I haven't read The Emperor's New Mind, but I suspect Penrose was simply highlighting the lack of physical meaning in a simultaneity convention. I can't believe Penrose (he of the Penrose diagrams) was seriously troubled by it.

Regarding the paper Rietdijk, C. Wim (1966) "A Rigorous Proof of Determinism Derived from the Special Theory of Relativity", Philosophy of Science, 33 (1966) pp. 341–344.

My answer to that would be "SR is only spacetime geometry!" It's simply not possible that the postulates of SR could lead to universal determinism. The postulates don't say nearly enough about the laws of physics even to come close to such a conclusion. If you start with the postulates of SR and end up with universal determinism, then you must have lost the plot somewhere along the way. Where do QM and the laws of Thermodynamics apply?

The laws of physics play out with (locally at least) Minkowski spacetime as the stage. Minkowski spacetime does not determine the laws of physics. They need to be discovered separately, and cannot, and this is where physics and philosophy diverge, be deduced or proved by pure thought.

The stage itself cannot determine the nature of the play that is acted out upon it.

 

[alexandrinushka]

Please go read the Insights article I linked to. I avoided loaded words in the article, but I agree with @PeroK that the error the argument makes is pretty simplistic. Even brilliant people can make simplistic mistakes.

@PeterDonis yes, you are right, I have promised to read it and come back afterwards, sorry. I admit I have read, twice, several hours ago, yet missed the main point.
So you claim that there is a tacit second premise in the argument.
1. Simultaneity is relative
2. All events in the past lightcone of a person at a moment in time are fixed
3. Therefore: all events in the universe, past, present and future, are set
It is the second claim that you question... Am I right?

 

[PAllen]

@PeterDonis yes, you are right, I have promised to read it and come back afterwards, sorry. I admit I have read, twice, several hours ago, yet missed the main point.
So you claim that there is a tacit second premise in the argument.
1. Simultaneity is relative
2. All events in the past lightcone of a person at a moment in time are fixed
3. Therefore: all events in the universe, past, present and future, are set
It is the second claim that you question... Am I right?

In my opinion, 1 and 3 are problematic. Simultaneity is not relative, it simply doesn’t exist except as a human convention. And 3 is a leap without foundation. As for 2, I have no problem with it.

 

[PeterDonis]

@PeterDonis yes, you are right, I have promised to read it and come back afterwards, sorry. I admit I have read, twice, several hours ago, yet missed the main point.
So you claim that there is a tacit second premise in the argument.
1. Simultaneity is relative
2. All events in the past lightcone of a person at a moment in time are fixed
3. Therefore: all events in the universe, past, present and future, are set
It is the second claim that you question... Am I right?

No. The second claim you state is my alternative to the claim that is used to justify the argument I was refuting. The claim that is used in the argument I was refuting is: 2. All events to the past of the surface of simultaneity of a person at a moment in time are fixed.

 

[PeterDonis]

In my opinion, 1 and 3 are problematic. Simultaneity is not relative, it simply doesn’t exist except as a human convention.

In the argument I was refuting, 1. is simply taking relativity of simultaneity in SR, in the way it is usually treated, as given. I did not cast any doubt on that particular premise in the Insights article. I agree simultaneity is a convention, but as it is usually used in SR (i.e., as it is defined by inertial frames), it is a relative convention, so to speak.

And 3 is a leap without foundation.

As I said in the article, if the premise 2. as it is used in the argument I was refuting (see my post #30 just now), is accepted as true, then the block universe interpretation does follow. But, as I said in the article, premise 2. as it is used in the argument I was refuting is not logically required by SR. It's an extra premise that is smuggled into the argument. If you replace it by my alternate premise 2., the one about past light cones, the argument falls apart; then 3. is indeed a leap without foundation, as you say.

 

[alexandrinushka]

No. The second claim you state is my alternative to the claim that is used to justify the argument I was refuting. The claim that is used in the argument I was refuting is: 2. All events to the past of the surface of simultaneity of a person at a moment in time are fixed.

Hold on, just to make sure I am getting you. You are saying that the original argument cuts too broad an area around a person's event to include a bit too much in it, whereas in your scenario you only demand that past lightcones be fixed, a much narrower zone, that thus evades the final conclusion, right?

 

[PAllen]

In the argument I was refuting, 1. is simply taking relativity of simultaneity in SR, in the way it is usually treated, as given. I did not cast any doubt on that particular premise in the Insights article. I agree simultaneity is a convention, but as it is usually used in SR (i.e., as it is defined by inertial frames), it is a relative convention, so to speak.

Yes, but I think it is important also to emphasize the personal choice involved. In particular, a person riding a bike back and forth is likely to choose Earth centered coordinates to do local physics. If interested in the solar system, they might choose sun centered coordinates. If interested in stars in the milkyway, they might choose milkyway centered coordinates. These are all free choices depending on convenience for a problem, and none of them carries any physical significance whatsoever, in particular, no such choices determine what is fixed and determined.

 

[PeterDonis]

You are saying that the original argument cuts too broad an area around a person's event to include a bit too much in it, whereas in your scenario you only demand that past lightcones be fixed, a much narrower zone, that thus evades the final conclusion, right?

Basically, yes. But the key difference is that the past light cone of a given event is invariant, whereas surfaces of simultaneity are frame-dependent (or, if you prefer, simultaneity convention dependent). So saying that the past light cone of a given event is fixed is an invariant statement, whereas saying that all events to the past of a surface of simultaneity that contains a given event is not.

 

[PAllen]

It occurs to me that one could even choose to claim that everything not in my causal future is fixed and determined, and then the whole andromeda argument still breaks down completely. It only works by attaching significance to categories that are have no physical significance in relativity: coordinate present, past, and future

 

[PeterDonis]

It occurs to me that one could even choose to claim that everything not in my causal future is fixed and determined, and then the whole andromeda argument still breaks down completely.

The andromeda argument as it is usually given does (sort of--but see comments at the end below), but your claim leaves open a slightly different argument that does not break down. If, for example, all events not in the causal future (i.e., past light cone plus spacelike separated "elsewhere") of the Andromedans launching the space fleet are fixed and certain, that includes events in our causal future here on Earth. And similarly for us with regard to events in the causal future of the Andromedans launching the fleet. What's more, there will be events in "elsewhere" of both Earth and Andromeda, which are now, by this new premise, taken to be fixed and certain, whose "elsewhere" region includes the arrival of the Andromedan space fleet on Earth (just pick an event far enough away from both Earth and Andromeda). So this alternative premise does not avoid the block universe conclusion. (Basically, this alternative premise is where the block universe argument I described ends up, once you add relativity of simultaneity to the premise that all events to the past of any surface of simultaneity are fixed and certain. That's why it leads to the same conclusion.)

 

[PAllen]

The andromeda argument as it is usually given does (sort of--but see comments at the end below), but your claim leaves open a slightly different argument that does not break down. If, for example, all events not in the causal future (i.e., past light cone plus spacelike separated "elsewhere") of the Andromedans launching the space fleet are fixed and certain, that includes events in our causal future here on Earth. And similarly for us with regard to events in the causal future of the Andromedans launching the fleet. What's more, there will be events in "elsewhere" of both Earth and Andromeda, which are now, by this new premise, taken to be fixed and certain, whose "elsewhere" region includes the arrival of the Andromedan space fleet on Earth (just pick an event far enough away from both Earth and Andromeda). So this alternative premise does not avoid the block universe conclusion. (Basically, this alternative premise is where the block universe argument I described ends up, once you add relativity of simultaneity to the premise that all events to the past of any surface of simultaneity are fixed and certain. That's why it leads to the same conclusion.)

Yes, I see. It just leads to a version of the argument using invariants, rather than avoiding it entirely the way the past light cone boundary does.

 

[Dale]

I have never been comfortable with the whole “fixed and certain” past and uncertain future anyway. If the world is deterministic then isn’t the future fixed and certain regardless of the causal structure? And if the world is non-deterministic then is even the past certain? To me it seems disconnected with the causal structure of spacetime.

 

[PAllen]

I have never been comfortable with the whole “fixed and certain” past and uncertain future anyway. If the world is deterministic then isn’t the future fixed and certain regardless of the causal structure? And if the world is non-deterministic then is even the past certain? To me it seems disconnected with the causal structure of spacetime.

Interesting idea, but, in principle, now, I have information on everything in my causal past. It seems hard not to have this be fixed and certain. Even QM and QFT don’t change this, including entanglement.

 

[anuttarasammyak]

Referring to post #3, thanks for your clarification. Historically Michelson Morley experiment expelled LET, I understand. The experiment suggests that the ether is at rest for every observer. How is it possible when two bodies with the observants have relative velocity ?

 

[PAllen]

The andromeda argument as it is usually given does (sort of--but see comments at the end below), but your claim leaves open a slightly different argument that does not break down. If, for example, all events not in the causal future (i.e., past light cone plus spacelike separated "elsewhere") of the Andromedans launching the space fleet are fixed and certain, that includes events in our causal future here on Earth. And similarly for us with regard to events in the causal future of the Andromedans launching the fleet. What's more, there will be events in "elsewhere" of both Earth and Andromeda, which are now, by this new premise, taken to be fixed and certain, whose "elsewhere" region includes the arrival of the Andromedan space fleet on Earth (just pick an event far enough away from both Earth and Andromeda). So this alternative premise does not avoid the block universe conclusion. (Basically, this alternative premise is where the block universe argument I described ends up, once you add relativity of simultaneity to the premise that all events to the past of any surface of simultaneity are fixed and certain. That's why it leads to the same conclusion.)

A more succinct version of this argument is that any event in my causal future is within what is fixed and certain for some event within what is fixed and certain for me. So yes, you need to adopt past light cone as the fixed and certain boundary to avoid this.

 

[alexandrinushka]

Basically, yes. But the key difference is that the past light cone of a given event is invariant, whereas surfaces of simultaneity are frame-dependent (or, if you prefer, simultaneity convention dependent). So saying that the past light cone of a given event is fixed is an invariant statement, whereas saying that all events to the past of a surface of simultaneity that contains a given event is not.

To be honest, I am not sure that this weaker reading of Andromeda saves the uncertain future. I need to check and draw some diagrams myself and do some thinking. From what I remember from reading on it several years ago, I'd say that "no", even in this weaker reading we arrive to scenarios, where future must be fixed. But then again, I cannot affirm it with certainty. By the way, did you try to publish this refutation in order to get some P2P constructive criticism? I have a hard time believing that your alternative has evaded or hasn't crossed the minds of influential philosophers...

 

[PeterDonis]

I am not sure that this weaker reading of Andromeda saves the uncertain future.

I didn't say it did. My argument in the Insights article was not that the block universe is false. (Unfortunately, multiple people in the comment thread talked as though that was my argument, even though I repeatedly clarified that it wasn't.) My argument was simply that the block universe is not required by SR. It is not the only viewpoint that is logically consistent with SR. But it is a viewpoint that is logically consistent with SR, and I never said otherwise.

did you try to publish this refutation in order to get some P2P constructive criticism?

I didn't have to; I'm not the only one that's made those observations. IIRC there was at least one peer-reviewed paper linked to in the comment thread on the Insights article that made similar criticisms to mine.

 

[PAllen]

I didn't say it did.

It definitely saves the possibility of uncertain future. The proof seems trivial:

1) For me, what is fixed and certain is within my past light cone.
2) For any event in my past light cone, its past light cone is a subset of mine (trivial mathematics). Therefore, no event that is fixed and certain for me has events fixed and certain for it that are not already fixed and certain for me.

 

[PeroK]

To be honest, I am not sure that this weaker reading of Andromeda saves the uncertain future. I need to check and draw some diagrams myself and do some thinking. From what I remember from reading on it several years ago, I'd say that "no", even in this weaker reading we arrive to scenarios, where future must be fixed. But then again, I cannot affirm it with certainty. By the way, did you try to publish this refutation in order to get some P2P constructive criticism? I have a hard time believing that your alternative has evaded or hasn't crossed the minds of influential philosophers...

I don't want to change the subject too much, but let me try you with this "rigorous proof" that SR is inconsistent:

1) A spaceship flies past Earth at a speed of $\frac 4 5 c$, say. A clock on Earth and a clock on the ship are synchronised (this can be done locally).

2) The spaceship continues for $1$ year according to the onboard clock. During this time, the Earth clock runs slow (by a factor of $\frac 3 5$). According to the spaceship, therefore, the Earth clock reads only $\frac 3 5$ years.

3) At this point the spaceship passes another ship moving in the opposite direction at $\frac 4 5c$ relative to Earth. A clock on the inbound ship is locally synchronised with the one on the outbound ship. I.e. to read $1$ years.

4) The inbound ship continues towards Earth and flies past one year later according to the ship clock, which now reads $2$ years.

5) During the inbound journey, the Earth clock has been running slow with the same factor of $\frac 3 5$ according to the ship clock. The Earth clock reads $\frac 6 5$ years.

That could not be simpler: the Earth clock was always running slower than the relevant ship clock.

And, yet, according to the Earth clock, both ships' clocks were always running slower.

That is as clear a contradiction as one could hope to find, isn't it?

I'm interested what you think about that?

 

[alexandrinushka]

I don't want to change the subject too much, but let me try you with this "rigorous proof" that SR is inconsistent:

1) A spaceship flies past Earth at a speed of $\frac 4 5 c$, say. A clock on Earth and a clock on the ship are synchronised (this can be done locally).

2) The spaceship continues for $1$ year according to the onboard clock. During this time, the Earth clock runs slow (by a factor of $\frac 3 5$). According to the spaceship, therefore, the Earth clock reads only $\frac 3 5$ years.

3) At this point the spaceship passes another ship moving in the opposite direction at $\frac 4 5c$ relative to Earth. A clock on the inbound ship is locally synchronised with the one on the outbound ship. I.e. to read $1$ years.

4) The inbound ship continues towards Earth and flies past one year later according to the ship clock, which now reads $2$ years.

5) During the inbound journey, the Earth clock has been running slow with the same factor of $\frac 3 5$ according to the ship clock. The Earth clock reads $\frac 6 5$ years.

That could not be simpler: the Earth clock was always running slower than the relevant ship clock.

And, yet, according to the Earth clock, both ships' clocks were always running slower.

That is as clear a contradiction as one could hope to find, isn't it?

I'm interested what you think about that?

This reminds me a bit about the twins' paradox, when one twin is older on return than the one staying on Earth. As far as I know, there are ways to resolve such scenarios within the framework of SR.
So wait... are you claiming SR is contradictory?

As for the Andromeda paradox you've quoted, I have not come up with an answer yet. To me @PeterDonis is proposing a different scenario, that might not lead to the same conclusion. But the question is actually: is the initial scenario, where one draws planes of simultaneity from each event valid. If you think they are then yes, the Putnam conclusion is unavoidable. If you question the legitimacy of drawing such planes of simultaneity (and I think you are), then the conclusion does not follow.
So if A is true (A being lack of absolute simultaneity), and B is true (the legitimacy of drawing a plane of simultaneity for each particular event), then C follows (block universe). And truly I do not think B is an "illegal" operation. But again, my thought process is not ripe in this regard, I need to come back to it.

 

[PeroK]

This reminds me a bit about the twins' paradox, when one twin is older on return than the one staying on Earth. As far as I know, there are ways to resolve such scenarios within the framework of SR.
So wait... are you claiming SR is contradictory?

What I'm saying is that if that confounds you, then you are in no position to evaluate the theory of SR. You're still at the "beginner student" level, struggling to grasp the nature of Minkowski spacetime.

Unless and until you have a mastery of the fundamentals, what you think about the theory is not very important. You need to learn and master the theory first.

 

[alexandrinushka]

What I'm saying is that if that confounds you, then you are in no position to evaluate the theory of SR. You're still at the "beginner student" level, struggling to grasp the nature of Minkowski spacetime.

Unless and until you have a mastery of the fundamentals, what you think about the theory is not very important. You need to learn and master the theory first.

You are write, I must master SR first before expressing myself on it.
Please note though that I have written your twin paradox has a resolution in SR and I've expressed a surprise about your claim.

 

[PeroK]

You are write, I must master SR first before expressing myself on it.
Please note though that I have written your twin paradox has a resolution in SR and I've expressed a surprise about your claim.

That is my version of the twin paradox. Of course, I wasn't the first to think of how to get rid of acceleration (or gravity) altogether. And, it shows why differential ageing and time dilation are actually fundamentally different.

My point is that it's impossible to identify the flaw in my argument without understanding the geometry of Minkowski spacetime. The same is true of the Andromeda paradox.

I'd make one final point. In classical physics, a (head-on) collision between two particles is entirely deterministic. Whereas, ironically given the above paper, a collision in SR becomes probabilistic. It takes QM to calculate the probabilities, but there is more than one possible outcome. For example, a single particle may remain as it is (the only possibility in classical mechanics); or, decay into two particles with less total rest mass. That's why someone writing a paper about SR implying determinism is a bit sad and funny. And, perhaps, "pathetic" is too strong a word!

And, just to note in passing, that the real use of SR is not directly as a theory of spacetime, but as a theory of energy-momentum. That's where its real importance lies. And, in fact, if you study particle physics or QFT (Quantum Field Theory), you will rarely see mention of "time dilation" or "length contraction" or "simultaneity". What you will be calculating are energy-momentum four-vector relationships - which are at the heart of these advanced subjects.

That's another reason that the endless analysis of time and space by non-physicists is a bit of a side-show. Although physicists who present popular science must take a fair share of the blame. The thing that really matters is the updated theory of energy-momentum to replace Newton's laws.

PS I admit that I'm being slightly disingenuous here, in that the above paper deals with a different idea of determinism. Nevertheless, I still think it's quite amusing!

 

[Dale]

However, I don’t think that the OP is expressing any anti-SR sentiment. Rather that based on the reading they have done they think a non-aether version of SR requires the block universe which they don’t like, and a non-block-universe version of SR requires an aether which they worry is too ad hoc. I think they accept SR as a fact either way, and just worry about the philosophy.

@alexandrinushka please correct me if I have misjudged your intention here in any way.