Is the Principle of Relativity Valid for Faster-than-Light Propagation?

[nikeadidas]

Michelson Morley experiment was sought to find out Earth's motion through ether, which allegedly produced ether wind. Thus the time required for two rays of light would be different, thereby producing interference pattern. Since Earth revolves arouns sun, and sun revolves around something else, and our galaxy is rotating, revolving. So is it not that if there was any ether wind, it would be the resultant of all these motion, and not just Earth's motion around sun. The equations in the textbooks take into account only the Earth's motion. I agree it is not possible to take into account all these motions while calculating ether wind. But I think it would render the calculations made for these experiments invalid. Had M&M factored this in their experiment..I am confused

 

[Matterwave]

They detected NO ether wind, period. So, either the Earth with all these combined motions is somehow "absolutely stationary" wrt to this ether, or there is no such thing as ether.

 

[ghwellsjr]

Isn't it possible that the combination of all the motions you described resulted in such a low value for the ether wind that the accuracy of the MMX instrument couldn't detect it?

Actually, you left out the most important motion which is the surface of the Earth caused by its rotation. So even if all the motions added to zero at some point in time, twelve hours later, it should have been large enough for the instrument to measure.

Michelson concluded that since he couldn't measure any ether wind, the Earth must be dragging the ether along with it. He proposed repeating the experiment at the top of a high mountain to minimize the drag.

But before he could carry out his proposal, some other scientists explained the null result of the experiment, not by discarding the idea of an absolute stationary ether, but by concluding that lengths must contract along the direction of motion through the ether. And that is exactly the same "explanation" that you get when you use Special Relativity to define any inertial Frame of Reference and see what happens when the surface of the Earth and thus the MMX instrument are moving in that FoR.

So if Special Relativity comports with reality, it also comports with the idea of an absolute stationary ether as it only affirms the fact that its state cannot be determined. It is discarded on philosophical preference, not on the result of any measurement.

 

[jtbell]

Actually, you left out the most important motion which is the surface of the Earth caused by its rotation. So even if all the motions added to zero at some point in time, twelve hours later, it should have been large enough for the instrument to measure.

They also tried it at different times of year, when the Earth is at different points in its orbit, so the Earth's orbital velocity was in different directions with respect to the supposed "ether wind" and the two would add differently.

 

[Dale]

If the aether breaks wind in the forest and there is nobody around to hear, is the speed of light still c?

 

[ghwellsjr]

If the aether breaks wind in the forest and there is nobody around to hear, is the speed of light still c?

Don't you mean "smell"?

 

[Dale]

Hehe, I was debating which to say.

 

[ghwellsjr]

It's a tough philosophical question but I recommend using Occam's razor to cut the wind.

 

[nikeadidas]

Yes totally correct. Guess I was confused about what I was exactly confused about. The thing that keeps nagging me is how M&M experiment is described in textbooks. I mean if the ether wind can arise anyhow, then isn't it naive to assume that the light ray traveling in the direction of motion would be traveling slowly compared that with the light ray traveling perpendicular to it. Wasn't it possible that due to uneven ether wind, the speed of light traveling perpendicular to motion would be faster?

I know that this notion about ether has been abandoned now. But I am looking at it just for sake of that experiment. Can anybody elucidate me on this (I hope I am being clear, coz this is as articulate as I can be)

 

[ghwellsjr]

Remember that a round trip of light is always involved so even if the light ray traveling in the direction of motion is slowed down, the light ray that is reflected back will be sped up, making the round trip take the same time as the rays involved in the perpendicular direction. But this requires that the mirrors be closer together along the direction of motion compared to the mirrors along the perpendicular.

 

[kill_SR]

It's funny how relativist like to talk about "null results" in M&M experiment but "forget" about Dayton Miller's "Ether-Drift Experiments at Mount Wilson"

 

[Doc Al]

It's funny how relativist like to talk about "null results" in M&M experiment but "forget" about Dayton Miller's "Ether-Drift Experiments at Mount Wilson"

Not as funny as those still desperately clinging to the Ether.

As far as Miller's results go, see: http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html#Miller

 

[ZapperZ]

And just in case people missed it, Doc Al's reference clearly falsify the notion that we "forget" about Miller's result. People who make such claim clearly haven't done their homework.

Zz.

 

[zonde]

I mean if the ether wind can arise anyhow, then isn't it naive to assume that the light ray traveling in the direction of motion would be traveling slowly compared that with the light ray traveling perpendicular to it. Wasn't it possible that due to uneven ether wind, the speed of light traveling perpendicular to motion would be faster?

Speed of light in direction of motion is c-v for forward trip and c+v for backward trip. So the round trip speed is $c(1-v^2/c^2)$.
In perpendicular direction speed for forward trip and backward trip is the same - $\sqrt{c^2-v^2}$
or $c\sqrt{1-v^2/c^2}$ and it is faster.

So it is correct that the speed of light traveling perpendicular to motion would be faster.

I know that this notion about ether has been abandoned now. But I am looking at it just for sake of that experiment. Can anybody elucidate me on this (I hope I am being clear, coz this is as articulate as I can be)

This actually has nothing to do with aether. It's about Galilean transformation.

 

[Tracer]

They detected NO ether wind, period. So, either the Earth with all these combined motions is somehow "absolutely stationary" wrt to this ether, or there is no such thing as ether.

This interpretation is based on the concept that the ether is stationary and unmoving. Other interpretarions are possible if the ether is considered to exist and have the ability to move. Why are these other interpretations taboo?

 

[ghwellsjr]

They detected NO ether wind, period. So, either the Earth with all these combined motions is somehow "absolutely stationary" wrt to this ether, or there is no such thing as ether.

This interpretation is based on the concept that the ether is stationary and unmoving. Other interpretarions are possible if the ether is considered to exist and have the ability to move. Why are these other interpretations taboo?

The whole idea of an ether is that it is what undulates or what waves. Just like waves on the surface of the water medium, the light wave travels at some speed, but the medium itself stays put. Having a medium that can move around would create more problems than it would solve.

By the way, prior to Einstein, most if not all scientists still believed in an absolute stationary ether. They explained the fact that no ether wind could be detected because their apparatus shrunk along the direction of motion through the ether and clocks would run slower when moving through the ether. This idea, called Lorentz Ether Theory or LET explains everything just as well as Special Relativity but it affirms the existence of the ether. Only problem is, no one knows where its rest state is so it has been deemed of no consequence, whether or not it actually exists.

 

[Tracer]

The whole idea of an ether is that it is what undulates or what waves. Just like waves on the surface of the water medium, the light wave travels at some speed, but the medium itself stays put. Having a medium that can move around would create more problems than it would solve.

By the way, prior to Einstein, most if not all scientists still believed in an absolute stationary ether. They explained the fact that no ether wind could be detected because their apparatus shrunk along the direction of motion through the ether and clocks would run slower when moving through the ether. This idea, called Lorentz Ether Theory or LET explains everything just as well as Special Relativity but it affirms the existence of the ether. Only problem is, no one knows where its rest state is so it has been deemed of no consequence, whether or not it actually exists.

Lorentz Ether Theory also assumes an absolute stationary ether. The CMBR is a good starting point for consideration as the rest frame of the ether. If it is not the correct rest frame it is the very next best thing for consideration.

If a quanta of ether contained energy, why would not that quanta be accelerated by a gravitational field exactly the same as any other object having mass or energy equivalent mass? It should be since the acceleration caused by a gravitational field is independent of the mass or energy equivalent mass of the body being accelerated.

In short, other than not being the mainstream consensus, why is the concept of moving space wrong?

 

[Dale]

In short, other than not being the mainstream consensus, why is the concept of moving space wrong?

Because it has failed every experimental prediction that it has made.

Also, if the idea is that light is a vibration in the aether medium then the aether needs to be solid since light is a transverse wave and fluids don't support transverse waves, and it needs to be both very rigid and low-density to get waves propagating at c.

 

[ghwellsjr]

LET, like SR, does not include and, in fact, ignores gravity, which means they don't apply to the whole universe or anything as big as CMBR.

In any case, both LET and SR do not consider a frame (or ether) to contain anything that could be quantized and as I said before, having a moving frame (or ether) in which parts of it can move around would create problems that the simple construct of a frame couldn't handle.

If something isn't mainstream consensus, there's usually a good reason.

 

[Histspec]

If a quanta of ether contained energy, why would not that quanta be accelerated by a gravitational field exactly the same as any other object having mass or energy equivalent mass? It should be since the acceleration caused by a gravitational field is independent of the mass or energy equivalent mass of the body being accelerated.

In short, other than not being the mainstream consensus, why is the concept of moving space wrong?

Because the (old) theory of "complete aether drag" is incompatible with
a) Aberration of light
b) Sagnac effect due to Earth's rotation (included in GPS)

This was the reason, why the Fresnel-Lorentz idea of a stationary aether was preferred - until it was refuted by Michelson-Morley, so that the only remaining choice was special relativity.

http://en.wikipedia.org/wiki/Aether_drag_hypothesis
http://en.wikipedia.org/wiki/Michelson–Gale–Pearson_experiment

Regards,

 

[zonde]

This interpretation is based on the concept that the ether is stationary and unmoving. Other interpretarions are possible if the ether is considered to exist and have the ability to move. Why are these other interpretations taboo?

This interpretation is based on the concept that matter is completely independent of aether. Aether is viewed as something like air - where there is matter there is no aether.

But this interpretation is very primitive considering modern concepts about chemical structure of material objects. Basically chemical bonds are of electromagnetic nature therefore chemical structure should be affected by changes in speed of light (not mentioning that aether as medium for electromagnetic field should be even inside atom).

And if you consider things that way difference between Einstein's spacetime and luminuferous aether is not obvious.

 

[Chronos]

Google on 'gravity probe B' for a more compelling discussion.

 

[Saw]

the Fresnel-Lorentz idea of a stationary aether was preferred - until it was refuted by Michelson-Morley, so that the only remaining choice was special relativity.

http://en.wikipedia.org/wiki/Aether_drag_hypothesis
http://en.wikipedia.org/wiki/Michelson–Gale–Pearson_experiment

The MM experiment did not refute LET. Since LET and SR use the same math, that means they are experimentally indistinguishable. If so, LET has not been refuted by any experiment, just as SR has not.

The Wikipedia link you mention does not contradict what I have just said. See this other Wikipedia link for a more detailed explanation.

The difference between LET and SR is only that the former ventures to put on the table an explanation for the math (there is a stationary and non-ponderable aether), albeit admitting it is unprovable (because such aether is undetectable), whilst the latter does not go into that complication and remains at an abstract level (that is the way the universe works: principle of relativity plus the constancy of the speed of light, full stop).

Somehow paradoxically SR is preferred for that very same reason, for its prudence: as Lorentz himself acknowledged, if you admit the hypothesis of the aether, you start wondering about its attributes and you waste your time in useless discussions.

 

[Dale]

The difference between LET and SR is only that the former ventures to put on the table an explanation for the math (there is a stationary and non-ponderable aether), albeit admitting it is unprovable (because such aether is undetectable), whilst the latter does not go into that complication and remains at an abstract level (that is the way the universe works: principle of relativity plus the constancy of the speed of light, full stop).

The latter also puts an explanation for the math, as you yourself have indicated.

 

[Saw]

The latter also puts an explanation for the math, as you yourself have indicated.

Yes, but of a different level. Am I wrong if I assume that LET also endorses the two postulates? If so, on top of that, it puts forward a deeper level explanation, meaning one that could be the reason for the fact that the two postulates are true. Couldn't we say that the postulates are kinematics and the aether is an attempt at grasping the dynamics? (In any case, to avoid any doubt: I am not defending the idea of an aether...!)

 

[Dale]

Am I wrong if I assume that LET also endorses the two postulates?

Yes, that is incorrect. LET assumes that Maxwell's equations are only valid in the aether frame, so it rejects the first postulate. The strange properties of the aether are proposed in order to make it so that even though Maxwell's equations are only valid in the aether frame our clocks and rulers are distorted in such a manner as to make it impossible to detect the deviations from Maxwell's equations in different frames.

Neither theory is any "deeper" than the other. Both use the same equations, one derives them from two postulates, the other postulates an aether which has those properties. Neither explains why the postulates are the way they are nor why the aether has the properties it has.

 

[ghwellsjr]

LET assumes that Maxwell's equations are only valid in the aether frame, so it rejects the first postulate. The strange properties of the aether are proposed in order to make it so that even though Maxwell's equations are only valid in the aether frame our clocks and rulers are distorted in such a manner as to make it impossible to detect the deviations from Maxwell's equations in different frames.

I've been saying that LET assumes the principle of relativity, the same as Einstein's first postulate, which is what you ended up saying (it's impossible to detect deviations in different frames), but rather it's Einstein's second postulate (the propagation of light is c in all frames) that LET rejects and instead affirms a different second postulate (the propagation of light is c only in the aether frame). It's only the choice between these two second postulates that makes the two theories different.

Neither theory is any "deeper" than the other. Both use the same equations, one derives them from two postulates, the other postulates an aether which has those properties. Neither explains why the postulates are the way they are nor why the aether has the properties it has.

I would add that the net effect of Einstein's second postulate is that any inertial frame you want to pick has all the properties of the one elusive aether frame. And this is why Einstein pointed out in his 1905 paper introducing Special Relativity that this second postulate is "only apparently irreconcilable with the former". He's saying it seems impossible that any frame could be a candidate for the frame which LET claims is unique but it turns out that it is possible.

 

[Dale]

I've been saying that LET assumes the principle of relativity, the same as Einstein's first postulate, which is what you ended up saying (it's impossible to detect deviations in different frames)

I would say that for LET the impossibility of detecting deviations is a derived result, not an assumption. It is not uncommon that a set of axioms and theorems can be re-axiomatized such that some of the old axioms become theorems.

However, I must admit that I have never bothered to look for an "official" axiomatization of LET.

 

[DrGreg]

I was under the impression that LET postulates the existence of an aether such that:

• light speed is isotropic relative to the aether
• length contracts by the Lorentz factor relative to the aether
• time dilates by the Lorentz factor relative to the aether

(this is an incomplete list). The Principle of Relativity therefore becomes a derived result rather than a postulate. One ugly aspect is that if you want to extend LET to cover various branches of physics, you have to keep adding more postulates, e.g. that "mass dilates by the Lorentz factor relative to the aether" (equivalent to relativistic mass), etc, whereas Einstein's first postulate automatically encompasses all branches of physics.

I may be wrong, but I suspect there may never have been a rigorous statement of LET's postulates because the theory was abandoned before it gained much momentum.

 

[Dale]

That is in line with my impressions also.

 

[Histspec]

The MM experiment did not refute LET. Since LET and SR use the same math, that means they are experimentally indistinguishable.

I wasn't talking about LET. I was talking about the Fresnel-Lorentz idea of a stationary aether, which was considered an observable entity when it was developed in 1818 by Fresnel and 1892 by Lorentz. Of course, it was later (between 1892-1904) modified by including the Lorentz transformation and all of its effects, in order to explain Michelson-Morley, Trouton-Noble, etc.. Though the resultant theory, now called LET, was never considered a viable alternative to special relativity.

Regards,

 

[Saw]

I wasn't talking about LET. I was talking about the Fresnel-Lorentz idea of a stationary aether, which was considered an observable entity when it was developed in 1818 by Fresnel and 1892 by Lorentz. Of course, it was later (between 1892-1904) modified by including the Lorentz transformation and all of its effects, in order to explain Michelson-Morley, Trouton-Noble, etc..

Ah, sorry, I misinterpreted you.

Yes, that is incorrect. LET assumes that Maxwell's equations are only valid in the aether frame, so it rejects the first postulate. The strange properties of the aether are proposed in order to make it so that even though Maxwell's equations are only valid in the aether frame our clocks and rulers are distorted in such a manner as to make it impossible to detect the deviations from Maxwell's equations in different frames.

That may be a good historic account of how Lorentz's ideas developed: first, he said that the PoR (Maxwell's equations are valid in all frames) did not apply (the equations are only valid in the aether frame), later he changed his mind (the PoR applies in all frames, because -as you say- " it is impossible to detect the deviations from Maxwell's equations in different frames"). But in the end LET accepts the PoR, doesn't it? Really, if person A accepts a principle without giving a reason and person B gives a reason (good or bad) but also accepts the principle, one has to admit that both A and B accept the principle. I may agree with you that that the reason given by B (LET) is "contrived, artificial, wrong or whatever you want to call it", but still it is a reason, which is lacking in what we call today SR.

rather it's Einstein's second postulate (the propagation of light is c in all frames) that LET rejects and instead affirms a different second postulate (the propagation of light is c only in the aether frame). It's only the choice between these two second postulates that makes the two theories different.

I do not see that. Again, it may be historically true (is it? Poincaré did affirm the principle of the constancy of the speed of light in connection with the PoR). But in any case, I do not see how one could today defend the existence of an aether, defend the first postulate, defend the LT and not defend the constancy of the speed of light in all frames.

I would add that the net effect of Einstein's second postulate is that any inertial frame you want to pick has all the properties of the one elusive aether frame. And this is why Einstein pointed out in his 1905 paper introducing Special Relativity that this second postulate is "only apparently irreconcilable with the former". He's saying it seems impossible that any frame could be a candidate for the frame which LET claims is unique but it turns out that it is possible.

I fully agree with this idea, which you often repeat. The gist of Einstein's idea is that all frames measure as if they were at rest wrt an aether, no matter if the latter exists or not. That is why the they all measure c as the speed of light and they find fault in all other frames (lack of sync, TD and LC). But that is fully compatible with LET, isn't it? LET simply adds to that that, in its opinion, an aether does exist.

To sum up: I admit I am splitting a hair…

 

[Saw]

The Principle of Relativity therefore becomes a derived result rather than a postulate.

Yes, that is it.

One ugly aspect is that if you want to extend LET to cover various branches of physics, you have to keep adding more postulates, e.g. that "mass dilates by the Lorentz factor relative to the aether" (equivalent to relativistic mass), etc, whereas Einstein's first postulate automatically encompasses all branches of physics.

Well, yes, when you give reasons, the problem is that your conclusions are limited by the nature and robustness of your reasons. But you also have advantages: you do not admit absurd conclusions like time travel...

I may be wrong, but I suspect there may never have been a rigorous statement of LET's postulates because the theory was abandoned before it gained much momentum.

You are right. In fact, it may be not worthwhile to develop LET any further. As I said before, it is more pragmatic assuming, as we do, that the 2 postulates work and that is it. As long as one does not think that he is giving an explanation for the postulates when he is not.

 

[Dale]

But in the end LET accepts the PoR, doesn't it?

LET views the principle of relativity in the same way that NASA conspiracy theorists view the moon landings. They recognize that there is a lot of evidence for it, but they believe that all of the evidence is faked, and it irritates them that they can't prove it. I wouldn't call that "accepting".

As long as you have an aether you are rejecting the principle of relativity, at least philosophically. However, if you throw out the philosophical baggage of the aether and just concentrate on the math then LET takes time dilation and length contraction as postulates and derives the principle of relativity and the invariance of c. SR takes the principle of relativity and the invariance of c as postulates and derives time dilation and length contraction.

Neither is deeper than the other as far as that goes nor does either provide more "reasons" than the other, they simply swap the assumptions and the conclusions.

Woot! 10k posts!

 

[lugita15]

As long as you have an aether you are rejecting the principle of relativity, at least philosophically.

Not necessarily. Sound waves have a preferred frame, the rest frame of air, yet that doesn't invalid the principle of relativity, because the wave equation for sound waves is not a law of physics and thus does not need to be true in all frames. We could have had an analogous situation where Maxwell's equations needed to be modified in order for them to be true in all frames.

Neither is deeper than the other as far as that goes nor does either provide more "reasons" than the other, they simply swap the assumptions and the conclusions.

Lorentz's historical theory was "deeper" than SR in at least one sense: it tried to provide physical underpinnings for relativistic effects. For instance, Lorentz believed that a moving electron was compressed by its own electromagnetic field.