Exploring the Concept of an Ether vs. Fabric of Space-Time in LET and SR

[grav-universe]

LET, Lorentz ether theory, is identical to SR but invokes an ether as the cause of length contraction and time dilation with motion through the ether. With it, there are no strange conceptualizations according to each observer's own particular reality for what they observe of other frames, but measurements just work out naturally with a physical shortening of lengths in the direction of motion and a physical slowing of clocks, both on the order of sqrt[1 - (v/c)^2] with motion relative to the ether frame. This is much easier for classical thinkers to conceive since it provides a mechanism by which length contraction and time dilation take place while producing exactly the same predictions as SR. The same simultaneity issues and Lorentz transformations also arise if observers in each frame synchronize their clocks according to the Einstein simultaneity convention. The only problem is that a physical shortening of rulers and slowing of clocks by sqrt[1 - (v/c)^2] causes observers in every frame to view each other identically and also provides the same physics in every frame, which is a plus, but renders the ether as undetectable by any useful relative measurements of motion, so no one frame can conclude that they are at absolute rest with the ether. With no way to detect the ether, many say we might as well drop it altogether, resulting in SR, but then we would have no mechanism by which length contraction and time dilation can actually physically take place, leaving just some strange distorted concept of reality from each observer's own point of view. Simply extending SR to GR, however, quickly brings back some idea about the fabric of space-time, whereas gravity is considered to be the warping of the fabric of space-time. But whether it is called universal pressure, vacuum energy, ether, the fabric of space-time, etc, a rose by any other name...

Okay, so this is what I want to find out. We all know that LET is mathematically equivalent to SR. The question is, is the concept of an ether equivalent to that of the fabric of space-time? I have stated my own view on the matter and explained why I think so. Please choose one of the following and explain your answer.

A) The concept of an ether and that of the fabric of space-time are the same thing.

B) The fabric of space-time exists but an ether does not. Please explain the difference.

C) Neither the fabric of space-time nor an ether really exist. Please explain why.

 

[grav-universe]

I have added a public poll to the thread.

 

[D H]

What is with these silly polls?

 

[grav-universe]

What is with these silly polls?

Just trying to get a consensus and some type of explanation for something I've been wondering about for quite a while. For those that don't wish to post, a poll would be a quick and easy, perhaps fun way of responding.

 

[D H]

LET, Lorentz ether theory, is identical to SR but invokes an ether as the cause of length contraction and time dilation with motion through the ether.

THat is not quite correct. Length contraction and time dilation are axiomatic in LET. No explanation, no derivation; they just are. Those are rather ad hoc axioms, so that alone puts LET on a much worse footing than special relativity. Bad as that is, LET postulates an absolute reference frame, the aether rest frame. This aether rest frame is undetectable by any means because length contraction and time dilation hide it from us. This is the kiss of death for LET. It turns a theory with a very poor choice of axioms into a non-scientific theory. That central axiom, the aether rest frame axiom, is not falsifiable and hence LET is not science.

 

[grav-universe]

THat is not quite correct. Length contraction and time dilation are axiomatic in LET. No explanation, no derivation; they just are. Those are rather ad hoc axioms, so that alone puts LET on a much worse footing than special relativity. Bad as that is, LET postulates an absolute reference frame, the aether rest frame. This aether rest frame is undetectable by any means because length contraction and time dilation hide it from us. This is the kiss of death for LET. It turns a theory with a very poor choice of axioms into a non-scientific theory. That central axiom, the aether rest frame axiom, is not falsifiable and hence LET is not science.

Right, okay. I would say, though, that the mathematics of LET, at least, can be determined directly from observation. Lorentz determined it from the electro-magnetic fields of electrons moving at a relative speed, I think. The mathematics can also directly be determined by assuming a precisely null result for the M-M experiment and/or the same two postulates of SR, and further experiments confirm the results in the same way as they do for SR. The only difference is that LET assumes an ether as the cause of length contraction and time dilation, although the ether itself cannot be detected with the way the mathematics works out, that is correct, but I would not say it isn't science to assume a mechanism exists in order to produce such distortions of space-time, otherwise each observer's realities just operate in some strange way that we cannot fully explain except to simply describe it mathematically with SR. Anyway, that is my opinion on the matter but it is not the subject of this thread. The question is whether the fabric of space-time can be considered the same as an ether. Apparently your response would either be B or C, but I cannot determine which. Could you please tell me which response you would go with and why?

 

[grav-universe]

Let me ask this as a separate issue. What if I were to drop the idea of an ether, but say that the fabric of space-time physically causes objects to length contract and time dilation to occur? Would that be acceptable within SR?

 

[D H]

The only difference is that LET assumes an ether as the cause of length contraction and time dilation

Not true. LET does not attribute any cause to length contraction or time dilation. Those two phenomena just exist in LET: They are axiomatic in LET.

but I would not say it isn't science to assume a mechanism exists in order to produce such distortions of space-time

First and foremost science must be testable and conceptually falsifiable. The absolute rest frame in LET is neither testable nor falsifiable. LET is not science.

 

[Dale]

I know what Lorentz's aether is, but I have never been clear on what the fabric of spacetime is. It seems more like a bumper-sticker slogan than a actual scientific concept.

 

[atyy]

Here I mean modern LET (not the historical ones held by Lorentz)- say like Bell's "How to teach special relativity" or Rindler's "every inertial frame is as good as absolute space". LET implies SR and SR implies LET, so there is no difference. You use whichever makes the calculation easier.

 

[grav-universe]

Not true. LET does not attribute any cause to length contraction or time dilation. Those two phenomena just exist in LET: They are axiomatic in LET.

I do not understand. Why would it be called ether theory if these attributes are not considered properties of the ether?

First and foremost science must be testable and conceptually falsifiable. The absolute rest frame in LET is neither testable nor falsifiable. LET is not science.

Okay well, fair enough I guess, although I still disagree because it provides a physical mechanism rather than just strange unexplainable distortions of reality. Anyway, my question to you is this. What then, in that same context, do we consider to be the fabric of space-time?

 

[grav-universe]

I know what Lorentz's aether is, but I have never been clear on what the fabric of spacetime is. It seems more like a bumper-sticker slogan than a actual scientific concept.

Right. It seems to me that we may only have changed the name.

 

[grav-universe]

Here I mean modern LET (not the historical ones held by Lorentz)- say like Bell's "How to teach special relativity" or Rindler's "every inertial frame is as good as absolute space". LET implies SR and SR implies LET, so there is no difference. You use whichever makes the calculation easier.

That's true. I prefer LET because it makes more sense to me about what is actually taking place by supplying a mechanism, but the mathematics is the same either way.

 

[D H]

I do not understand. Why would it be called ether theory if these attributes are not considered properties of the ether?

The word theory in this context means a set of explanations that taken together explain some set of observed phenomena. Lorentz Ether THeory, like Newtonian mechanics, postulates an master inertial reference frame. The two theories differ in that Newtonian mechanics postulates Galilean relativity. LET replaces Galilean relativity with length contraction and time dilation as axioms.

There is no derivation of length contraction and time dilation from the concept of an aether rest frame in Lorentz Ether Theory. Length contraction and time dilation are axiomatic in that theory. Period.

Okay well, fair enough I guess, although I still disagree because it provides a physical mechanism rather than just strange unexplainable distortions of reality. Anyway, my question to you is this. What then, in that same context, do we consider to be the fabric of space-time?

Now you are mixing theories. It is general relativity, not special relativity, that talks about curved space-time. Space-time is flat in special relativity.

 

[grav-universe]

The word theory in this context means a set of explanations that taken together explain some set of observed phenomena. Lorentz Ether THeory, like Newtonian mechanics, postulates an master inertial reference frame. The two theories differ in that Newtonian mechanics postulates Galilean relativity. LET replaces Galilean relativity with length contraction and time dilation as axioms.

There is no derivation of length contraction and time dilation from the concept of an aether rest frame in Lorentz Ether Theory. Length contraction and time dilation are axiomatic in that theory. Period.

That is very interesting if it is true, and I will have to look into it further. I hadn't considered that possibility before and have searched around some since you mentioned it, but have not yet found anything decidely one way or the other. I know that the ether was considered the medium for light, but if it is not considered to have any properties that actually affect time dilation and length contraction, then I can easily see why the idea of it would be dropped, since light could then just travel as photon particles which obey the same mathematics, so it wouldn't matter whether or not it exists, since it would have no direct consequences. I still don't know why it would be called ether theory in that case, though.

Okay, so that expands our choices here a bit to the concept of an ether that is merely a medium for light but does not affect length contraction or time dilation in any way, another type of ether that does physically provide these properties as the mechanism, or nothing at all but distortions of reality. I am only interested in these last two, and of course a comparison to the fabric of space-time.

Now you are mixing theories. It is general relativity, not special relativity, that talks about curved space-time. Space-time is flat in special relativity.

Right, extending SR to GR gives us the fabric of space-time. So from your replies I take it that you would not consider the ether of Lorentz's day to be the same as the fabric of space-time the way the concepts are conceived. I can see why now, thank you. Okay, so new question. In SR, would you consider the fabric of space-time to be the physical cause of length contraction and time dilation, or would such a concept only be reserved for GR?

 

[grav-universe]

If what DH says is true, which I so far have no reason to believe otherwise, then my poll is now moot, depending upon the precise definition of an ether, and whether or not it directly physically causes length contraction and time dilation. Thank you for your replies, DH.

 

[Maui]

With no way to detect the ether, many say we might as well drop it altogether, resulting in SR, but then we would have no mechanism by which length contraction and time dilation can actually physically take place, leaving just some strange distorted concept of reality from each observer's own point of view.




C) Neither the fabric of space-time nor an ether really exist. Please explain why.

On such modern-day connundrums, I've found it much easier on the brain to think of 'reality' as FPS(same way your brain perceives it). Either way, we never perceive materials(matter) but information about 'them'(in fps). Perhaps information is primary to matter.

 

[Saw]

Not true. LET does not attribute any cause to length contraction or time dilation. Those two phenomena just exist in LET: They are axiomatic in LET.

DH, I do not understand why you say so.

It looks to me as if it were the other way round.

SR's postulates or axioms are (i) the principle of relativity and (ii) constant c for all observers. In turn (ii) can only happen if there is (iii) TD and LC.

But why (ii) and (iii)? Well, LET makes a hypothesis about the physical reasons: there is an absolute LC of bodies wrt the ether and an absolute TD, even if we are only able to measure the relative TD and LC, due to the relativity of simultaneity.

SR instead does not care for the reasons. It is contented with the postulates. But you cannot say that it is superior because it is less axiomatic. On the contrary, it is "superior", if you wish, because by being more axiomatic, it wastes less time on the characteristics of an ether which, apart from being quite elusive, apparently have no practical consequences.

 

[Dale]

Grav Universe, you keep talking about "fabric of spacetime" as though it is a meaningful term in modern physics. I have never used the concept and don't think it has a standard definition. I think a few pop-sci authors have used the phrase, but I have never seen a textbook define it.

 

[D H]

SR's postulates or axioms are (i) the principle of relativity and (ii) constant c for all observers. In turn (ii) can only happen if there is (iii) TD and LC.

Einstein derived length contraction and time dilation from the constancy of the speed of light. The motivation for that axiom is clear: Maxwell's equations. The motivation for time dilation and length contraction as axioms is clear as mud.

Ask any physicist which set of axioms is less ad hoc, which set of axioms is preferred.

Try to find Lorentz ether theory in any college text on relativity. You can't. It fell out of favor over a hundred years ago, only to be revived in our internet age by anti-relativistic crackpots.

Ask any physicist which of special relativity versus Lorentz ether theory is compatible with general relativity.

 

[Mentz114]

I get the impression that grav-universe thinks that LC and TD are detectable in the rest frame of the clock and ruler. Why else look for physical 'causes' of these phenomena, which are only observed from other frames ?

 

[Saw]

Einstein derived length contraction and time dilation from the constancy of the speed of light. The motivation for that axiom is clear: Maxwell's equations. The motivation for time dilation and length contraction as axioms is clear as mud.

Ask any physicist which set of axioms is less ad hoc, which set of axioms is preferred.

Try to find Lorentz ether theory in any college text on relativity. You can't. It fell out of favor over a hundred years ago, only to be revived in our internet age by anti-relativistic crackpots.

Again, it is the other way round, at least that is the general view that this forum takes or at least the view of very authoritative posters in physics forum.

Pop-sci books, internet simplifications argue: Maxwell's equations --> constancy of c --> TD and LC.

That is very misleading. Maxwell's equations do NOT logically require or imply constancy of speed of light in the sense of SR's second postulate. They only require that the speed of light is constant in the medium for light propagation, i.e. the ether, which Maxwell believed in.

If you wish to have Einstein's second postulate, i.e. constancy of c in all reference frames, you need one of this three:

(a) Postulate it as an axiom without any reason, in which case, once that such postulate is bought, you can mathematically derive TD and LC as well as RofS.

(b) Postulate the other things (TD and LC as well as RofS) as an axiom and then derive the constant c for all frames.

(c) Argue that the ether requires TD, LC and RofS for a physical reason and then derive the constant c for all observers.

I am not sure about Einstein himself. What I have checked so far (I would have to look for the citations) makes me think that his approach was closer to (c) than not. But what is yours? Is it (b)? Well, that is legitimate as well. But then you must admit that you are NOT disproving (c), just doing without it. The idea that the ether is disproved is a naïve mistake. There should be A FAQ against it. And it should be banned from textbooks as a fallacy.

 

[D H]

Pop-sci books, internet simplifications argue: Maxwell's equations --> constancy of c --> TD and LC.

That is not just a "pop-sci book, internet simplification". It is exactly the line of reasoning taken by Einstein in his 1905 paper.

Maxwell's equations do NOT logically require or imply constancy of speed of light in the sense of SR's second postulate. They only require that the speed of light is constant in the medium for light propagation, i.e. the ether, which Maxwell believed in.

Of course Maxwell believed in an aether. Whether light comprised particles or was a wave phenomenon was an ongoing debate from Newton's time on. Having derived a wave equation for light, Maxwell obviously fell in the "light is a wave phenomenon" side of the debate. As every other wave phenomenon known required some medium to carry the wave, it was only natural to assume that light too involved some transmission medium.

If you wish to have Einstein's second postulate, i.e. constancy of c in all reference frames, you need one of this three:

(a) Postulate it as an axiom without any reason, in which case, once that such postulate is bought, you can mathematically derive TD and LC as well as RofS.

Give that man a cigar! Sans your bit of appeal to ridicule, that is exactly what Einstein did in his 1905 paper.

So, let's look at your appeal to ridicule, the "without any reason" phrase. In a sense, all postulates are made "without any reason". They are not derived. They are givens. That said, the postulates of some theory of science should however be motivated by something physical. The assumption that the speed of light is the same to all inertial observers is clearly motivated by Maxwell's equations. That the speed of light is the same to all observers is right there in Maxwell's equations.

Maxwell's equations differ markedly from the mathematical description of all other wave phenomena in one key aspect. The speed at which other waves propagate depends on the speed of the observer with respect to the transmission medium. That is not the case in Maxwell's equations. The speed at which electromagnetic propagate is c, period. The speed of the observer does not appear in those equations.

Einstein's insight was to take the constancy of the speed of light as a given. It is not a rabbit he pulled out of some axiomatic hat. That axiom is very well motivated.

I am not sure about Einstein himself. What I have checked so far (I would have to look for the citations) makes me think that his approach was closer to (c) than not.

Wrong. Have you taken any college physics beyond freshman physics? The derivation of length contraction, time dilation, and the relativity of simultaneity is standard fare in the classical mechanics class taken by physics majors at the sophomore/junior level. Einstein's two axioms are very simple, (a) the principle of relativity, that the laws of physics are the same in all inertial frames, and (b) the constancy of the speed of light, as motivated by Maxwell's equations. He did not assume length contraction or time dilation in his 1905 paper. He derived them.

 

[Fredrik]

We all know that LET is mathematically equivalent to SR.

I don't actually. I've been told that it makes the same predictions as SR, and that it involves a preferred inertial frame, but I've never seen a definition of the theory. If someone can give me a reference, I'd appreciate it.

A) The concept of an ether and that of the fabric of space-time are the same thing.

It clearly isn't. Spacetime is a smooth manifold, and that ensures that no coordinate system is "preferred".

B) The fabric of space-time exists but an ether does not. Please explain the difference.

C) Neither the fabric of space-time nor an ether really exist. Please explain why.

Science doesn't tell us what "really exists", or what anything "really is". Theories make predictions about results of experiments, and experiments find out how accurate the predictions are. They can't tell us if the mental images we have in our minds when we think about a theory represent something "real" or not. So it doesn't make sense to ask if objects corresponding to those images "really exist". We should only be asking if those images are useful, in the sense that they help us understand the theory. If someone thinks a mental image of an ether makes some problems easier to understand intuitively, I wouldn't tell that person that he's wrong to use it.

 

[Fredrik]

The absolute rest frame in LET is neither testable nor falsifiable. LET is not science.

I think this claim is too strong. A theory needs to make predictions about results of experiments, but I see no need to require that every concept used in the definition of the theory gives us more predictions. The definition of "theory" that I use includes a requirement that none of the axioms that define the theory can be removed without changing or removing predictions from the theory. (I don't want "QED+an invisible blue giraffe that doesn't interact with matter" to be considered a theory). So if the preferred frame can be removed from LET without changing or removing some of the theory's predictions, then I would agree that it doesn't qualify as a theory. But it seems to me that if we just remove this axiom, what we have left either doesn't make any predictions at all, or makes infinitely many conflicting predictions, depending on how you look at it. So this axiom is an essential part of the theory, and the theory is falsifiable even if some of the individual axioms aren't.

If LET isn't a theory because it has an axiom that can't be falsified, then I would say that SR isn't a theory either. What about the smooth structure of Minkowski spacetime? It contains infinitely many coordinate systems. I could pick any of them and say that the claim that this one exists isn't falsifiable.

 

[grav-universe]

Grav Universe, you keep talking about "fabric of spacetime" as though it is a meaningful term in modern physics. I have never used the concept and don't think it has a standard definition. I think a few pop-sci authors have used the phrase, but I have never seen a textbook define it.

I am really just referring to space-time itself. The warping of the fabric of space-time is what is sometimes used to describe a gravitational field.

 

[D H]

That is the pop-sci explanation, grav_universe. Special relativity and general relativity are kinematic theories: They explain what happens, but not how/why it happen. They describe mathematically what is to be expected but do not say how those interactions come to be. Talking about the "fabric of space-time" is in a sense attributing a "how" without any underlying mechanism.

You see these pop-sci descriptions because the underlying mathematics are far, far, far beyond the grasp most people. The people who are conversant with the mathematics simply use those mathematical descriptions. They have no need for those somewhat vague and inevitably analogistic pop-sci descriptions. They know the math and they know how to use it.

 

[grav-universe]

I don't actually. I've been told that it makes the same predictions as SR, and that it involves a preferred inertial frame, but I've never seen a definition of the theory. If someone can give me a reference, I'd appreciate it.

It's simple really. Just apply the same mathematics of SR, but to the mechanism of an ether. Imagine such a preferred inertial frame. An ether is stationary to that frame and light always travels at c through the ether. Any body that travels through the ether is physically contracted in the line of motion and physical processes slow down due to the effects of the ether upon the body, whereas rulers shrink and clocks slow, each by sqrt[1 - (v/c)^2]. Observers within each frame synchronize their clocks by applying the Einstein simultaneity convention. Now, by using those same physically shrunken rulers and slowed clocks, observers in other frames will also measure the same things of the preferred frame, the same relative speed, and same length contraction and time dilation, as well as the same simultaneity differences and the same isotropic speed of light, and they will observe the same things for all other frames, depending upon the relative speed between those frames, although this unfortunately renders the ether undetectable. This can all be demonstrated mathematically in precisely the same way as with SR. So with or without the ether, the mathematics works out exactly the same when applying the same time dilations and length contractions. The only difference is that an ether supplies a mechanism, something which physically produces these effects, while SR discounts the ether, leaving only strange unexplained distortions of reality within each particular frame.

It clearly isn't. Spacetime is a smooth manifold, and that ensures that no coordinate system is "preferred".

Observations and experiment wouldn't allow us to determine any absolute frame either way, so all frames would be the "preferred" frame equally, but the same coordinate systems would work out with LET or SR. As far as being smooth, an ether would also be smooth on a macro-scale, although on a micro-scale it might be prone to quantum effects for the discrete individual quantities that compose it.

Science doesn't tell us what "really exists", or what anything "really is". Theories make predictions about results of experiments, and experiments find out how accurate the predictions are. They can't tell us if the mental images we have in our minds when we think about a theory represent something "real" or not. So it doesn't make sense to ask if objects corresponding to those images "really exist". We should only be asking if those images are useful, in the sense that they help us understand the theory. If someone thinks a mental image of an ether makes some problems easier to understand intuitively, I wouldn't tell that person that he's wrong to use it.

Right. All we really know are the observations we make, and everything else is a mental construct, and even our own perceptions come into questions sometimes. Models change and the mathematics is altered, so we might become relunctant to determine what is real and what is not. I personally define what is real by anything that produces a physically change upon something else or constrains it in some way. That applies equally to particles, fields, as well as space-time, the only difference being that particles and fields have a location, whereas we can't point here or there and say "that is space-time", because it is everywhere. Still, space-time affects matter and energy in a very definite way, it constrains the speed of light and particles, it warps and it expands, so as far as I am concerned, it is real, it exists, it applies a mechanism.

 

[grav-universe]

That is the pop-sci explanation, grav_universe. Special relativity and general relativity are kinematic theories: They explain what happens, but not how/why it happen. They describe mathematically what is to be expected but do not say how those interactions come to be. Talking about the "fabric of space-time" is in a sense attributing a "how" without any underlying mechanism.

You see these pop-sci descriptions because the underlying mathematics are far, far, far beyond the grasp most people. The people who are conversant with the mathematics simply use those mathematical descriptions. They have no need for those somewhat vague and inevitably analogistic pop-sci descriptions. They know the math and they know how to use it.

Exactly. The math is the most important part of the description for a model, regardless of the precise details. Noone knows what space-time really is, so they are mostly content with just examining the mathematics and direct observations, only describing things otherwise for visual content for those that do not know the math, but also knowing that however they describe it is most likely wrong, just an analogy which begins to fall apart as soon as those same people they described it to begin to ask more questions about it, making many relunctant to go much beyond the mathematics to begin with. Some, however, I believe have gone too far by considering the mathematics and observations the only things that are "real", not wanting to venture much further. I think it is time to go beyond that, even if only just a little, in order to try to determine what space-time really is and how it affects matter and energy the way it does.

 

[D H]

What do you think the people are doing at the LHC? Twiddling their thumbs?

 

[D H]

Not to mention the even larger number of physicists working on string theory, loop quantum gravity, and similar concepts that are attempting to go beyond the standard model.

 

[grav-universe]

I have continued to look around for any reference about whether Lorentz's ether had a direct effect upon bodies with motion through the ether. I found a couple that stated it did, but that could be a misconception on part of the author, although I would think I would also find at least one website that states it to be a common misconception in that case, which I did not. Anyway, I decided to go straight to the source. http://en.wikisource.org/wiki/Electromagnetic_phenomena" is Lorentz's 1904 paper. A couple of sentences down, he states "The first example of this kind is Michelson's well known interference-experiment, the negative result of which has led FitzGerald and myself to the conclusion that the dimensions of solid bodies are slightly altered by their motion through the aether." I also found many other statements, some made by Einstein himself who seems to have had doubts, which suggest that eventually Einstein was also leaning more toward the ether of Lorentz than his own Relativity.

 

[Saw]

General comment: I think that the questions and comments by grav-universe are well posed and should be encouraged. Maybe they can be improved, refined, but at no rate should they be treated dismissively.

In this line, sorry, DH, let me fight your dismissals.

On the one hand, you admit that your approach is not based on any physical reason, on any physical hypothesis about the “whys”:

Special relativity and general relativity are kinematic theories: They explain what happens, but not how/why it happen. They describe mathematically what is to be expected but do not say how those interactions come to be. Talking about the "fabric of space-time" is in a sense attributing a "how" without any underlying mechanism.

As I expressly mentioned, I think that such approach is perfectly legitimate. Working on the basis of postulates, for which the reason is not specified, is a common and acceptable method. Afterwards observation confirms or not and that is it. “Whatever works”, like the film says. I never said that is ridiculous.

However, on the other hand, you want to live in the best of the worlds. You want to dismiss grav-universe because he looks for reasons, but when you discuss with me you want to asseverate that you do have some physical reasons for your postulates. I do not know why but you do think that the ether is a ridiculous candidate for that purpose, don’t you? And then you find a better candidate:

The assumption that the speed of light is the same to all inertial observers is clearly motivated by Maxwell's equations. That the speed of light is the same to all observers is right there in Maxwell's equations.

Maxwell's equations differ markedly from the mathematical description of all other wave phenomena in one key aspect. The speed at which other waves propagate depends on the speed of the observer with respect to the transmission medium. That is not the case in Maxwell's equations. The speed at which electromagnetic propagate is c, period. The speed of the observer does not appear in those equations.

You are mistaken. As you yourself noted, Maxwell believed in an ether. And he believed that the speed of light of his equations was c only in the ether frame. A different thing is that Einstein realized that, if c were to vary depending on the reference frame, that might be a threat to the principle of relativity. Why so is a subtle issue whose discussion we can skip for the time being. (After all, the speed of sound is different in all frames moving relative to the air and nobody thinks that such fact ruins the principle of relativity…) Anyhow, he rightfully found that contradiction. And that is why he postulated that c is the same for all observers. By doing so he did not simply repeat Maxwell’s laws. He added a new postulate to them, one that reconciles them with relativity. I do not think this is controversial.

Conclusion:

- Yes, today's mainstream science does not care for the why of SR, it just provides a mathematical description.

- The so called LET is exactly the same as that plus an attempt at providing a why (by reference to the ether).

- This ether model, as you yourself accept, has a didactic value = it helps to better visualise the consequence of the formulas.

- Does it have a predictive value? In my opinion, it might have one in cases where absurd consequences fit within the math. For me an example of this is time travel: even if the formulas admitted it, I think it is absurd and I rely for this purpose on the conceptual foundation that the ether model provides. But that is another and a long story... The point is that the ether model does not only help to understand the math, it also puts boundaries to its meaning.

 

[D H]

You want to dismiss grav-universe because he looks for reasons, but when you discuss with me you want to asseverate that you do have some physical reasons for your postulates.

No, I am dismissing Lorentz Ether Theory because it is a dead-end theory based on two incredibly ad hoc axioms and one non-scientific axiom. There is no forward path with Lorentz Ether Theory.

The assumption that the speed of light is the same to all inertial observers is clearly motivated by Maxwell's equations. That the speed of light is the same to all observers is right there in Maxwell's equations.

Maxwell's equations differ markedly from the mathematical description of all other wave phenomena in one key aspect. The speed at which other waves propagate depends on the speed of the observer with respect to the transmission medium. That is not the case in Maxwell's equations. The speed at which electromagnetic propagate is c, period. The speed of the observer does not appear in those equations.

You are mistaken.

Mistaken? About what? That Maxwell's equations makes no allowance for the speed of the observer? It is very clear that they don't. The speed of the observer never enters the equations. That Einstein wasn't strongly motivated by Maxwell's equations in his choice of the invariance of the speed of light as an axiom? Read his 1905 paper. The second half is entirely devoted to Maxwell's equations.

As you yourself noted, Maxwell believed in an ether. And he believed that the speed of light of his equations was c only in the ether frame.

Maxwell believed in an ether for the simple reason that all other wave phenomena require a medium. After the fact, no such medium is required. We now know that the photon is the quantum of electromagnetic interactions -- something that Maxwell couldn't have known. Photons don't require a physical medium. They move through space. The luminiferous aether as proposed and modified by those end of the 19th century physicists cannot be detected, is not needed, and is not scientific.

 

[Saw]

Let us make it clear. I have no belief in the ether. I just say that there is no reason to dismiss it as a model, which would have the advantages stated above: its being didactic and its serving to rule out absurd consequences that the math itself does not rule out.

No, I am dismissing Lorentz Ether Theory because it is a dead-end theory based on two incredibly ad hoc axioms and one non-scientific axiom. There is no forward path with Lorentz Ether Theory.

You repeat yourself without answering my comments. In the context of the ether model, TD, LC and RofS are not simply axioms. You have not reflected about it but that is not our problem. Why don't you make a try? If you did, you would understand that those consequences are not arbitrary inventions but flow easily from the assumption of such model. And why should we assume the said model if the ether is not detectable? Well, it is a falsifiable hypothesis! Nothing that the history of science has not witnessed thousands of times.

Mistaken? About what? That Maxwell's equations makes no allowance for the speed of the observer? It is very clear that they don't. The speed of the observer never enters the equations.

One thing is that the speed of the observer does not enter the equations and another different thing would be that the observer should observe the same speed. As I said, the equation for the speed of sound does not include the speed of the observer but that does not mean that the speed of sound is the same in all frames.

That Einstein wasn't strongly motivated by Maxwell's equations in his choice of the invariance of the speed of light as an axiom? Read his 1905 paper. The second half is entirely devoted to Maxwell's equations.

If you take the stance of appealing to the authority of the master, then you should read all his papers, not only what he wrote when a young investigator wanting to impress his audience. (Even then, as far as I remember, he never said that the ether is disproved, only that we could "dispense with" it.) As the OP has hinted at, Einstein later on looked on the ether under a more favourable light. Ok, he said, our attempts to discover the properties of the ether have led to many difficulties. Discouraged by this, we have banned the word from our vocabulary. Instead we will simply say that "space" has the property to transmit EM waves. But we should not deceive ourselves: by eliminating the word, we have not eliminated the problem.