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Following up on this question on whether it's possible to construct a physical theory with invariant space-time and variable speed of light.

I am looking for a authoritative and more definitive answer to the hopefully more precise question:

Are Lorentz ether theory and special relativity fully compatible/interchangeable?

Interchangeable in the sense that, at least in principle,there is either no different prediction the other doesn't make or if there is it could be settled experimentally (or has been) in favor of one of the two?

From the wikipedia page I gather that they are indistinguishable, but SR is preferred over LET either for practical reasons (elegance, convenient) or because it's assumption are somewhat less arbitrary or don't require somewhat problematic entities such as ether.

Qmechanic
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8 Answers8

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Are Lorentz ether theory and special relativity fully compatible/interchangeable? Interchangeable in the sense that, at least in principle,there is either no different prediction the other doesn't make or if there is it could be settled experimentally (or has been) in favor of one of the two?

Special relativity (SR) uses the Lorentz transform to make all of its experimental predictions. Lorentz aether theory (LET) also uses the Lorentz transform to make all of its experimental predictions. Furthermore, the reading of a clock or a ruler would be mapped to the same variable in both and also a given reference frame would either be determined to be inertial or non-inertial for both.

As a result, there is simply no possible way to distinguish between the two experimentally. Any result that is predicted by one is predicted by the other also. Their disagreements are entirely philosophical or metaphysical. Due to that fact it is sometimes considered that both LET and SR are simply different interpretations of the same theory (usually confusingly called SR).

Here is a solid reference describing the experimental equivalence and the philosophical distinction between the two:

http://philsci-archive.pitt.edu/5339/1/leszabo-lorein-preprint.pdf

Dale
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Lorentz ether theory describes a world in which light moves through a medium called ether, and observers that are not at rest with respect to this ether see everything Lorentz transformed. In some philosophical sense, there is a preferred reference frame: that in which the ether is at rest.

But the funny thing about Lorentz transformations is precisely that they relate reference frames in which light moves in the same way; the speed of light does not change upon applying your favorite Lorentz transformation. For this reason, it is not possible even in principle to determine experimentally what the ether rest frame is, since even light (the stuff that the ether was invented for) moves in the same way in different inertial reference frames.

The theory of special relativity explains all of this more naturally by postulating that all inertial reference frames are similar and that there is no ether, at least not one that sets one specific reference frame apart. One could try to argue that the electromagnetic field as found in quantum electrodynamics can be called an 'ether'; however, since the electromagnetic field does not have one specific inertial frame it likes to live in, this is mostly semantics.

Stijn B.
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No, for one very simple reason: the equations he derived from his theory for electromagnetism are non-relativistic: i.e. the equations actually posed by Maxwell in his treatise with the correction by Heaviside and Thomson, rather than their relativistic counterparts: Maxwell-Minkowski equations.

I laid out a Rosetta Stone between Lorentz' Attempt of a Theory of Electrical and Optical Phenomena in Moving Bodies in my reply The Rosetta Stone For Lorentz showing that, in fact, his equations are just the Maxwell-(Heaviside-)Thomson equations, not the Maxwell-(Einstein-Laub-)Minkowski equations. Written in Abschnitt II of his article, Lorentz' equations are: $$\begin{align} Ⅰ_b\ & \text{Div}\ = ρ \\ Ⅱ_b\ & \text{Div}\ ℌ = 0 \\ Ⅲ_b\ & \text{Rot}\ ℌ' = 4πρ + 4π\dot{} \\ Ⅳ_b\ & \text{Rot}\ = -\dot{ℌ} \\ Ⅴ_b\ & = 4πV^2 + [·ℌ] \\ Ⅵ_b\ & ℌ' = ℌ - 4π[·] \\ Ⅶ_b\ & = + [·ℌ] \end{align}$$

Reiterating what I noted in my reply about his notation, his "Div" is our $∇·(\_)$, his "Rot" is our $∇×(\_)$, where $$∇ = \left(\frac{∂}{∂x}, \frac{∂}{∂y}, \frac{∂}{∂z}\right),$$ his $\dot{(\_)}$ is our (and his) $∂/∂t$, and his $[\_·\_]$ is our $(\_)×(\_)$, so that he could have just as well have written $[∇·\_]$ for "Rot". Strangely, now that I think about it, I don't recall seeing any instance of the vector dot product anywhere in his article! Otherwise, he could have written "Div" as $∇·(\_)$, alongside $[∇·\_]$ for "Rot". I will use the dot product, while retaining his notation elsewhere. So $(\_)·(\_)$ means our dot product, but $[(\_)·(\_)]$ means his cross product.

Finally, his $V$ is our $1/\sqrt{με}$; that is: the wave speed for the underlying medium. In vacuum, $V = 1/\sqrt{μ_0ε_0} = c$.

The Heaviside/Thomson correction is the $-4π[·]$ term in $Ⅵ_b$. Without it, Lorentz' equations are equivalent to the ones Maxwell actually listed in his treatise, which Maxwell went through pains to show have symmetry under the Galilean transform (or would - if you add in the Heaviside/Thomson correction - that was an oopsie on Maxwell's part).

By the way, the counterpart $(\_)_a$ equations are those for the "stationary frame" - i.e. the frame where $ = 0$. That, right there, is already a strong clue telling you that Lorentz is still couched in the world of non-relativistic physics, notwithstanding the mental gymnastics of his narrative.

The correct equations - when written in his notation - that accord with the theory of Relativity are the same as above except for $Ⅴ_b$ and $Ⅵ_b$, which have to be changed to: $$\begin{align} {Ⅴ_b}'\ & = 4πV^2 + [·ℌ] - \frac{V^2}{c^2}[·ℌ'], \\ {Ⅵ_b}'\ & ℌ' = ℌ - 4π[·] + \frac{[·]}{c^2}, \end{align}$$ which will make this equivalent to the equations laid out independently by Einstein & Laub, and by Minkowski around the same time in the 1907-1908 period - the Maxwell-Minkowski equations.

The other equations don't need to be changed ... because they are invariant under arbitrary coordinate transformations, which can be displayed in manifest form by writing them in the language of differential forms. Only $Ⅴ_b$ and $Ⅵ_b$ break this symmetry and make a distinction between the relativistic versus non-relativistic forms of Maxwell's Theory.

For the relativistic versions ${Ⅴ_b}'$ and ${Ⅵ_b}'$, the relations in a vacuum reduce to: $$V = c,\quad = 4πc^2, \quad ℌ' = ℌ,$$ the vector $$ becomes "superfluous" (to use Einstein's term) and none of Lorentz' mental gymnastics are required. The distinction between the relativistic and non-relativistic versions can be put into sharp relief by using the parameter $α = 1/c^2$ for the relativistic case, and $α = 0$ for the non-relativistic case, writing equations $Ⅴ_b/{Ⅴ_b}'$ and $Ⅵ_b/{Ⅵ_b}'$ in combined form as: $$\begin{align} Ⅴ_{bα}\ & = 4πV^2 + [·ℌ] - αV^2[·ℌ'], \\ Ⅵ_{bα}\ & ℌ' = ℌ - 4π[·] + α[·]. \end{align}$$ These equations go with a space-time geometry that has the following as its invariants: $$ dt^2 - α\left(dx^2 + dy^2 + dz^2\right),\\ dt \frac{∂}{∂t} + dx \frac{∂}{∂x} + dy \frac{∂}{∂y} + dz \frac{∂}{∂z},\\ \left(\frac{∂}{∂x}\right)^2 + \left(\frac{∂}{∂y}\right)^2 + \left(\frac{∂}{∂z}\right)^2 - α \left(\frac{∂}{∂t}\right)^2 $$ as its invariants.

Under a Galilean transform $$ → - t,\quad t → t$$ (where $ = (x, y, z)$) we have the following transform: $$ \dot{(\_)} → \dot{(\_)} + ·∇, \quad \text{Div} → \text{Div}, \quad \text{Rot} → \text{Rot}, \\ → , \quad ℌ' → ℌ' - 4π[·],\\ ℌ → ℌ, \quad → + [·ℌ], \\ \quad ρ → ρ, \quad → , \\ \quad → - , \quad → + , \quad V → V$$ and - as you can clearly see - his equations are invariant under them; though $Ⅲ_b$ and $Ⅳ_b$ take a little vector algebra to see it and require application of $Ⅰ_b$ and $Ⅱ_b$, respectively.

To show that it's actually the modified equations that are Relativistic, rather than the equations Lorentz wrote down, it's easiest to set $α = 1/c^2$ and write the Lorentz transforms in infinitesimal form as: $$Δ = -t,\quad Δt = -α·.$$ Then, under these transforms: $$ Δ\dot{(\_)} = ·∇(\_),\quad Δ\text{Div} = α·\dot{(\_)},\quad Δ\text{Rot} → α\left[·\dot{(\_)}\right],\\ Δ = \frac{α\left[·ℌ'\right]}{4π},\quad Δℌ' = -4π[·],\\ Δℌ = α[·],\quad Δ = [·ℌ],\\ Δρ = -α·ρ, \quad Δ = α[·[·]],\\ Δ = - + α·,\quad Δ = - α·,\quad ΔV = 0, $$ the modified equations will be invariant - but not Lorentz' equations.

In other words: Lorentz' equations are not invariant under the Lorentz transformations! It's the modified equations which are. His theory is non-relativistic.

Therefore, Lorentz' aether theory is not equivalent to Special Relativity and is - in fact - not even Relativistic at all, but non-Relativistic.

If he had been able to use his aether theory to derive the correct equations ${Ⅴ_b}'$, and ${Ⅵ_b}'$, instead of $Ⅴ_b$, and $Ⅵ_b$, then we could have said that Lorentz' theory was equivalent to Special Relativity. But he simply derived the wrong equations - the non-relativistic ones, and all of his mental gymnastics were for nought.

NinjaDarth
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The mathematical predictions of LET and SR are indistinguishable, but there are big philosophical differences. I will point out some of the philosophical differences here.

For the purpose of this discussion, let's imagine there is some God like entity (GLE) that can see the ether or preferred reference frame (PRF). Mathematically we can pick any inertial reference frame to be the preferred reference frame and the results will be the same, but for convenience we choose the average rest frame of the entire universe to be the rest frame of the ether that the GLE sees. Let's consider 3 rockets A, B and C, all with a length of 100 metres when at rest with respect to (WRT) the PRF. A and B are initially at rest WRT to the PRF and C is moving at 0.8 WRT the PRF. In LET, the real length of C is 60 metres due to its motion relative to the ether. C's rulers are also length contracted and his clocks are time dilated due to his motion relative to the ether and due to the fact the speed of light is constant relative to the ether, C measures his own rocket to still be 100 metres long, (but the GLE knows he is wrong). B accelerates to match C's velocity. B is now also length contracted to 60 meters according to the GLE, but B thinks he is still 100 metres long and at rest and that his own proper acceleration (which he can measure) caused rockets A and B to and the rest of the universe to accelerate and length contract. In LET the only thing that changed during B's acceleration is B himself. B experienced proper acceleration so B is the object that actually changed length and the rest of the universe remained where it was. That is philosophically reasonable.

Notice I said "changed length" instead of length contracted. C who up to now has been travelling at 0.8c relative to the ether but imagine himself to be stationary now decides to accelerate to 0.8c to catch up with A. He experiences proper acceleration and imagine he is increasing his velocity but the GLE knows he decelerating WRT the ether and his length is actually increasing. C does not consider himself to be expanding and also imagines the entire universe has contracted due to his own acceleration. In LET, the only thing that changed length was C because he was the only thing that experienced proper acceleration. Sometimes, when you experience proper acceleration you length contract contract in LET because you are increasing your velocity relative to the ether and sometime your length contract because you are decreasing your velocity relative to the ether and we mere mortals are not privileged to know how our velocity changed relative to the ether. Unlike the GLE, we cannot know if our proper acceleration caused length expansion or length contraction, but philosophically it is reasonable to assume that the object that experiences proper acceleration is the one that changes length for greater or smaller and that accelerating ourselves does not actually accelerate and length contract the entire universe, even though it appears that way. SR's philosophy is that if we measure the entire universe to length contract because we have accelerated, then the universe has really length contracted because what we measure is what is real. Perhaps it is more fair to say that SR takes the position that since we are not GLEs and cannot know what is really happening, we will ignore the philosophical worries of what is really happening and concentrate only on what can be measured.

It is the same for time dilation. In LET our clock rate is at a maximum when at rest WRT to the ether and time dilation is unambiguously determined by our motion relative to the ether. When we experience proper acceleration our clock rates change but unlike the GLE we do not know if our acceleration caused us to increase or decrease our speed relative to the ether because we don't know where the ether is. All we can do is compare our clock relative to other clocks (that may or may not be moving relative to the ether. This is why when two observers are moving away from each other, it is ambiguous as to which one has the slower clock rate because we have no way of truly answering that question by making a measurement.

In SR, A can measure B's clock to ticking slower than his own clock and B can measure A's clock to be ticking slower than his own clock.
In LET, B's clock can really be ticking slower than A's clock, because of motion WRT the ether, but B's slower clock (and length contraction and relativity of simultaneity) cause B to measure A's clock to be ticking slower.

In SR, A can measure B to be length contracted relative to himself and B measures A to be length contracted.
In LET, B's ruler can really be shorter than A's ruler, because of motion WRT the ether, but B's shorter ruler (and time dilation and relativity of simultaneity) cause B to measure A's ruler to be shorter.

In SR, the acceleration of an observer can cause the the whole universe to length contract and time dilate.
In LET, the acceleration of an observer can only change the length of the observer and his rulers and his clock rates and this causes him to measure the the universe as length contracted and time dilated while in reality the universe remains as it was.

In SR, the speed of light is constant relative to any observer, which is slightly paradoxical if you think about it.
In LET, the speed of light is constant relative to the ether. Any observer moving relative to the ether, has the illusion of seeing the speed of light as constant relative to themselves, because their rulers are length contracted and their clocks are time dilated, due to their motion relative to the ether.

In LET, length contraction and time dilation only happens to rulers and clocks that directly experience proper acceleration, and acceleration of an observer cannot directly cause physical changes to distant objects that do not experience proper acceleration.

You can use LET to secretly make calculations (just pick any inertial reference frame to be the PRF) and get a sense of what is really happening (or at least get a handle on why some things are unmeasurable and unknowable and apparently seemingly contradictory in SR) and then revert to SR before you publish in public, because mentioning LET is emotive and socially unacceptable in physics circles.

If there really is a creator of the universe, it is amusing to think he created the laws of physics in such a way that no matter how smart we evolve to be and no matter how advanced our computing technology and knowledge is, we can never determine what exactly is really happening, to keep us humble and know who is Boss. The many interpretations of quantum physics, the uncertainty principle, the halting problem, the undecidable problem and Gödel's incompleteness theorem also remind us of that.

KDP
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No. Such equivalence is inconsistent with Galilean principle: inertial observers are equivalent, and there's no physical processes lest you difference between beying at rest or moving with constant speed.

kakaz
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It seems to me that an experimental distinction between SR and LR was discovered and articulated 50 years ago by Hafefe and Keating.

They could NOT use SR to predict their experimental results. They could only use a theory which, like LR, posited a preferred frame (which is strictly forbidden by SR).

The LR theory pre (post) dicted the actual clock differences which occurred. Again, SR could not do so.

This is explained in one of the footnotes to their paper, which references Builder, the physicist. As you may know, Builder is the physicist who did an extensive analysis of SR in 1957 in a paper entitled "Ether and Relativity." He concluded that "The observable effects of absolute accelerations and of absolute velocities must be ascribed to interaction of bodies and physical systems with some absolute inertial system....There is no alternative to the ether hypothesis."

The preferred frame used by Hafefe and Keating was the ECI, as is also used as a preferred frame of reference by the GPS. As with the H-K experiment, special relativity CANNOT be used by the GPS as a theoretical basis for predictions. Like it or not, it must employ a neo-lorentzian theory to obtain reliable results.

The ultimate test of one competing theory against another is the predictive ability of each. Philosophical maxims, like Occam's razor, cannot be determinative. When one theory gives you correct predictions pertaining to empirical phenomena, and the other doesn't, that's the ballgame, right there.

Jack
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In the context of theories of relative motion, the word "ether" simply refers to a "truly" motionless frame of reference.

For decades, astrophyicists and cosmologists have used the CMB as a preferred frame of reference (i.e., a so-called "ether").

George Smoots (and his team) received a Nobel Prize in Physics for his extensive experimentation (over a course of many years) showing the the CMB is indeed what has been called "the rest frame of the universe." So, here again, an experimental differentiation of SR from LR has been established.

Here's an excerpt from Smoots' paper on the topic:

"We attribute the dipole anisotropy to the motion of the Earth and Solar System relative to the universal CMB radiation field and thus the distant matter in the Universe. This would seem to violate the postulates of Galilean and Special Relativity but there is a preferred frame in which the expansion of the Universe looks most simple. That frame is the average rest frame of the matter and CMB and from that frame the expansion is essentially isotropic." https://aether.lbl.gov/www/projects/u2/

Smoot is effectively referring to absolute, not relative, motion here. Without at least the tacit assumption of a bona fide rest frame ("ether") physics would be impossible.

Jack
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In my prior answer, referring to the analysis of Hafele and Keating regarding their famous "clocks on jets" experiments, I said: "They could NOT use SR to predict their experimental results. They could only use a theory which, like LR, posited a preferred frame (which is strictly forbidden by SR)."

This post was met with dismissive, hand-waving denial by some members. I'm not convinced that those posters read (or remembered) the analysis in question, however. For that reason I am elaborating on the basis of the statement made in my original answer.

Here is a link to a blog post offered a physicist, identity unknown to me, which discussed this issue in some depth. http://www.conspiracyoflight.com/Hafele/HafeleKeating.html Here are a few relevant quotes from that submission:

"Hafele, Keating and Builder make some categorically un-relativistic statements, namely:

  1. Inertial motion can only be referenced to the physically privileged frame of the “universe” which is an absolute inertial system.

  2. The “absolute velocities” must mean motion with respect to this absolute frame of reference.

  3. There is no alternative to the ether hypothesis....

The Hafele and Keating experiment implies that the earth’s pole, or more perfectly, the fixed stars,* compose the only frame where Einstein synchronization doesn’t break down...

Only if the clocks are synchronized to the Earth Centered Inertial (ECI) frame of reference (i.e. the pole of the earth) do these inconsistencies become manageable.

However, this is tantamount to establishing the ECI frame as a preferred reference frame for motion above all others. [emphasis added]

Although the Hafele and Keating experiment did confirm the gravitational time dilation effect on clocks predicted by Einstein, the velocity time dilation predictions of special relativity (1905) at low velocities would seem to have been proven wrong...

The Sagnac term [employed by H & K] is at odds with a fundamental tenet of relativity theory by requiring an absolute frame of reference for both rotational and inertial motion, defining the latter as relative to a non-rotating universal frame...

If an argument is going to be made that a speed of light test is invalid because the frame is rotating, or the observer is rotating, then we have to discard all speed of light tests to date since every place that humans have performed a test on the earth or in near space have always been experiencing some form of rotation, either diurnal or orbital, which in modern times has become readily visible. As Hafele and Keating say in their paper, inertial motion must be referenced to a universal reference frame.

[Allan, Weiss and Ashby] said that the principle of the constancy of the speed of light leads to a prediction of the Sagnac effect in rotating systems; this is an interesting comment since the constant speed of light in their example is in the non-rotating frame of reference - i.e. the frame of the fixed stars just as in Fig. 4 above. This underlines the extent to which "relativistic" has become interchangeable with "absolute."

===end of quotes====

As you can see for yourselves, this author claims that the additional equations created by H & K operate to disconfirm 5 specific predictions of SR as presented by Einstein (without a "sagnac factor").

The original question was: "Are Lorentz ether theory and special relativity fully compatible/interchangeable?" Again this author comments that "This underlines the extent to which "relativistic" has become interchangeable with "absolute."

So I guess the question cannot really be properly addressed unless people agree on what conceptual differences exist, if any, between Lorentzian Relativiy and Special Relativity.

From my experience, there appears to be a substantial disagreement about that. Many have assured me that the the H-K experiment "confirms" SR. On the only hand the experimenters themselves (H & K) seem to undermine that claim. Some seem to think that if the lorentzian transformations are employed, then the theory being employed is "special relativity," but clearly that does not necessarily follow.

Jack
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