Any plausible explanation for dynamical length contraction?

In summary: 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...
  • #1
alexandrinushka
66
16
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.
 
Last edited:
  • Skeptical
Likes PeroK
Physics news on Phys.org
  • #2
I know SR is special relativity and QM is quantum mechanics but do not know LET. Could you teach me what it is?
 
  • #3
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.
 
Last edited:
  • Like
Likes pbuk and anuttarasammyak
  • #4
alexandrinushka said:
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.

alexandrinushka said:
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"?
 
  • Like
Likes alexandrinushka
  • #5
Dale said:
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.
 
  • #6
Dale said:
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.
 
  • #7
alexandrinushka said:
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.
 
  • Like
Likes vanhees71
  • #8
Dale said:
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?
 
  • #9
alexandrinushka said:
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?
 
  • Like
Likes vanhees71 and alexandrinushka
  • #10
PeterDonis said:
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).
 
  • #11
alexandrinushka said:
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.
 
  • Like
Likes DaveE, vanhees71 and alexandrinushka
  • #12
alexandrinushka said:
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.
 
  • Like
Likes vanhees71 and alexandrinushka
  • #13
alexandrinushka said:
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.
 
  • Like
Likes DaveE, vanhees71 and alexandrinushka
  • #14
Dale said:
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.
Dale said:
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.
 
Last edited:
  • #15
  • #16
alexandrinushka said:
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.

alexandrinushka said:
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.
 
  • Like
Likes hutchphd, Orodruin and vanhees71
  • #17
Dale said:
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
 
  • Skeptical
Likes PeroK
  • #18
alexandrinushka said:
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/
 
  • Like
Likes vanhees71, PeterDonis and alexandrinushka
  • #19
Dale said:
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.
 
  • #20
alexandrinushka said:
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.
 
  • #21
Dale said:
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.
 
  • #22
PAllen said:
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.
 
  • #23
alexandrinushka said:
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.
 
Last edited:
  • Like
  • Love
  • Informative
Likes martinbn, Klystron, PeterDonis and 5 others
  • #24
PeroK said:
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.
 
  • Skeptical
Likes weirdoguy
  • #25
alexandrinushka said:
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.
 
  • Like
Likes vanhees71
  • #26
alexandrinushka said:
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.
 
  • Like
Likes Dale and PeroK
  • #27
alexandrinushka said:
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.
 
  • Like
Likes Klystron, weirdoguy and alexandrinushka
  • #28
PeterDonis said:
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?
 
  • #29
alexandrinushka said:
@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.
 
  • Like
Likes Dale
  • #30
alexandrinushka said:
@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.
 
  • #31
PAllen said:
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.

PAllen said:
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.
 
  • #32
PeterDonis said:
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?
 
  • #33
PeterDonis said:
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.
 
  • Like
Likes PeroK
  • #34
alexandrinushka said:
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.
 
  • Like
Likes PeroK
  • #35
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
 

Similar threads

  • Special and General Relativity
2
Replies
54
Views
1K
  • Special and General Relativity
2
Replies
45
Views
3K
Replies
63
Views
3K
  • Special and General Relativity
Replies
12
Views
873
  • Special and General Relativity
Replies
12
Views
878
  • Special and General Relativity
Replies
11
Views
1K
  • Special and General Relativity
2
Replies
36
Views
2K
  • Special and General Relativity
Replies
11
Views
2K
  • Special and General Relativity
Replies
17
Views
2K
  • Special and General Relativity
Replies
34
Views
3K
Back
Top