Michelson–Morley experiment: Did it disprove the existence of ether?

[ghwellsjr]

The only difference between LET and SR is that LET postulates that there exists a single absolute ether rest frame in which the one-way speed of light is the same in all directions and SR postulates that in any inertial frame the one-way speed of light is the same in all directions, (but only one at at time). Ocam's razor prefers SR because it frees you up from trying to find that single illusive ether rest frame--any inertial frame will do.

No, unless you want to abandon SR, which I seriously doubt.

Hey ghwellsjr,
Still didn't forget the exercise...I will get there soon.

I have a question: What do you mean by "...(but only one at a time)...": one frame at a time, right? if you mean one frame at a time, does this restriction have a name? is it a result of an equation? or of an experiment? what is it called? what is the reason for it? what is the problem with having the speed of light the same at all frames at a once?


Thanks,
Roi.

Great questions, I'm glad I get the chance to answer them. Please note that we are talking here about two theories as opposed to experimental measurements which those theories explain. These two theories have as their foundation the abstract concept of frames of reference which are co-ordinate systems (spatial and time components) to enable us to deal with bigger situations than what we could deal with if we limited ourselves to just the data from experimental measurements.

So now let's lay aside the issue of these two theories and focus on experimental measurements. It turns out that any inertial observer (without any consideration for a frame) who attempts to measure the speed of light will get the constant value c, no matter which direction the measurement is made. Any number of inertial observers moving with respect to each other will get the same result simultaneously for similar experiments. Futhermore, if any number of these observers send similar timing signals between each other, they will each observe that the other one's timers are running slower than their own and by the same amount. If two inertial observers in relative motion happen to be co-located at the moment a flash of light is emitted, they will both observe that they are each located in the center of that expanding flash of light. There are many other experiments that can be performed of this nature that have nothing to do with any frames of reference--it's just the way nature works.

Now we'll look at how frames of reference enter into the picture. In an attempt to understand the apparent strange way that nature works, scientists have come up with theories:

In one of these, Lorentz Ether Theory (LET), it is postulated that there exists only a single absolute frame of reference in which light actually travels in all directions at the speed c and only when you are at rest in that frame will your measurements reflect what is really happening. All other inertially moving observers get the same results because nature is playing tricks on them by adjusting their clocks and rulers in such a way that they get the same results as they would get if they were stationary in the ether. In fact, since we don't know where the ether rest frame is, chances are, all observers are not at rest in the ether frame and so it's a safe bet that we all have our clocks and rulers modified.

Special Relativity, SR, on the other hand, postulates that you can consider anyone of the inertial observers to be at rest in the ether frame of reference where his measurements reflect what is really going on and all the other inertially moving observers are getting their clocks and rulers modified by nature in such a way that they get the same result as they would if they were at rest in the ether but the theory says that their clocks and rulers are actually getting modified, according to the one observer which we are considering to be at rest in the ether.

The theories include methods by which we can assign values to locations and clocks that include all observers and objects so that we can transform a scenario defined according to one frame of reference into any other frame of reference. We can even transform or define a frame of reference where there is no observer or object. The important thing to consider here is that you should not use the values for locations or times from two different frames and thereby see a contradiction--that's what all the so-called paradoxes do--you need to use only one frame at a time, it doesn't matter which one.

 

[harrylin]

I am glad to have my posts responded to even when the respond appears to be adverse.

There seems to be a misunderstanding.
I admit that subsequent work by Willem de Sitter laid emission theories to rest.

Yes there is a misunderstanding but I hope that you don't take it personal - at least, I don't.

What appears to have escaped your attention is that at the time of writing Michelson thought that the Fizeau experiment had definitely laid to rest ballistic emission theories - he did not seriously consider them. See next!

When I said I referred to the paper of Michelson and Morley as I wrote my post I
meant that I reread it (not that I quoted from it). The paper begins :

"The discovery of the aberration of light was soon followed by an explanation
according to the emission theory. ... difficulties in this apparently sufficient
explanation were overlooked [and are not specified in the paper] until after an
explanation on the undulatory theory of light was proposed. This new explanation was
at first almost as simple as the former. But it [the undulatory theory] failed to
account for the fact proved by experiment ... "

Ah, now we have found another cause of disagreement...
Aargh! you are right here, I did a too hasty copy-paste without checking the result - sorry for that! Regretfully I thus added to confusion, and I can likely not delete my mis-citation...
Never mind, I'll try to clean it up now!

The original undulatory theory was disproved and replaced by two competing ones (actually two classes, for there were more): the one of Stokes and the one of Fresnel. The one of Stokes was disproved in favour of that of Fresnel by the Fizeau experiment which Michelson re-enacted before doing the MMX.
However, the results of that same experiment (among others) were also in disagreement with common ballistic emission theories. That is what Michelson meant with:
"The difficulties in this apparently sufficient explanation were overlooked until after an explanation on the undulatory theory of light was proposed."

You can read his 1886 experiment here:
http://en.wikisource.org/wiki/Influence_of_Motion_of_the_Medium_on_the_Velocity_of_Light

Michelson wanted to test two hypotheses of Fresnel's ether theory. He had already obtained positive confirmation in 1886 of the second hypothesis. Therefore he wrote about MMX:
"The experimental trial of the first hypothesis [by Fresnel] forms the subject of the present paper."

Never mind, we seem to agree about their purpose - so let's move on.

the reconciliation of undulatory theory with experiment required, they tell us, two
hypotheses:

"first, the ether is supposed to be at rest except in the interior of transparent
media, in which secondly ... The experimental trial of the first hypothesis forms
the subject of the present paper."

They calculated the fringe shift expected under the first hypothesis, but experinent
found no shift instead.

This thread is about the implications of the experiment's outcome.

I detected an unstated assumption in their thinking: that measuring stick length is
not equivalent to radar ranging (that is, echo ranging with light). The essence of the experiment is a comparison of the two methods.

I also think the equivalence stands to reason: If the forces between atoms in a solid
are communicated at the speed of light, then the two methods would be equivalent. Only if the forces were instantaneously communicated would they be different as calculated by
Michelson and Morley.

Yes, that's basically Heaviside-Fitzgerald. And I think that I already showed agreement with your clarification (the one conclusion that remained, according to me, was that there is a greater correspondence of the two methods of length measurement than MMX had supposed).

 

[harrylin]

[..]

Special Relativity, SR, on the other hand, postulates that you can consider anyone of the inertial observers to be at rest in the ether frame of reference where his measurements reflect what is really going on and all the other inertially moving observers are getting their clocks and rulers modified by nature in such a way that they get the same result as they would if they were at rest in the ether but the theory says that their clocks and rulers are actually getting modified, according to the one observer which we are considering to be at rest in the ether. [..]

Actually, SRT never postulates "what is really going on": it postulates phenomena that will be observed (measured). In order to eliminate a suggestion of self contradiction I would modify your clarification as follows:

Special Relativity postulates that you can pretend anyone of the inertial observers to be at rest in the ether frame of reference so that all the other inertially moving observers are getting their clocks and rulers modified by nature in such a way that they get the same result as they would if they were at rest in the ether; the theory thus says that - according to the one observer which we are considering to be at rest in the ether - their clocks and rulers are actually affected by their motion.
And just as in Newtonian mechanics, any observer can pretend to be in rest so that it's the others that move - but if we pretend all to be at rest at the same time then we mess up!

 

[ghwellsjr]

That's fine, I accept your suggestion.

 

[thwle]

I like the tendency of recent posts so far as relativity is concerned, although I would argue that Occam's principle called for simplicity of theory not of application. Is SR really less simple? (retorical, doesn't belong in this thread.)

This thread being about the implications of MMX, I want to reassert my point of view that MMX demonstrates Lorentz contraction -- nothing more.

 

[harrylin]

I like the tendency of recent posts so far as relativity is concerned, although I would argue that Occam's principle called for simplicity of theory not of application. Is SR really less simple? (retorical, doesn't belong in this thread.)

This thread being about the implications of MMX, I want to reassert my point of view that MMX demonstrates Lorentz contraction -- nothing more.

It's an indirect demonstration of Lorentz contraction - based on our assumption that light propagation is fully unaffected by its motion wrt the source. Talking about relativity, Einstein put it as follows:

"for a co-ordinate system moving with the Earth the mirror system of Michelson and Morley is not shortened, but it is shortened for a co-ordinate system which is at rest relatively to the sun."
- http://www.bartleby.com/173/16.html

 

[thwle]

It's an indirect demonstration of Lorentz contraction - based on our assumption that light propagation is fully unaffected by its motion wrt the source. - http://www.bartleby.com/173/16.html

Hmmm. What does that mean?

Either:
(1) MMX demonstrates that speed of light relative to the MMX apparatus was the same in every direction.
or
(2) MMX demonstrates that solids undergo Lorentz contraction as they move relative to the frame of reference in which the speed of light is the same in every direction.

 

[thwle]

Talking about relativity, Einstein put it as follows:

"for a co-ordinate system moving with the Earth the mirror system of Michelson and Morley is not shortened, but it is shortened for a co-ordinate system which is at rest relatively to the sun."
- http://www.bartleby.com/173/16.html

This is not helpful. What shall be the standard of measurement. In MMX, there was no observer moving relative to the apparatus. The Lorentz contraction is not revealed by a measurment but by an invariance.

 

[thwle]

... [two] theories:

In one of these, Lorentz Ether Theory (LET), it is postulated that there exists only a single absolute frame of reference in which light actually travels in all directions at the speed c and only when you are at rest in that frame will your measurements reflect what is really happening. All other inertially moving observers get the same results because nature is playing tricks on them ... In fact, since we don't know where the ether rest frame is, chances are, all observers are not at rest in the ether frame and so it's a safe bet that we all have our clocks and rulers modified.

Special Relativity, SR, on the other hand, postulates that you can consider anyone of the inertial observers to be at rest in the ether frame of reference where his measurements reflect what is really going on and all the other inertially moving observers are getting their clocks and rulers modified by nature in such a way that they get the same result as they would if they were at rest in the ether but the theory says that their clocks and rulers are actually getting modified, according to the one observer which we are considering to be at rest in the ether.

So is the only difference that in SR we decide not to care that "we don't know where the ether rest frame is."

 

[harrylin]

This is not helpful. What shall be the standard of measurement. In MMX, there was no observer moving relative to the apparatus. The Lorentz contraction is not revealed by a measurment but by an invariance.

I find Einstein's clarification very helpful, as some people forget that MMX doesn't take the non-inertial Earth as reference. The standard reference system to which MMX refers is the solar system in which the Earth orbits - that's rather common in astronomy.

 

[harrylin]

[I wrote: "It's an indirect demonstration of Lorentz contraction - based on our assumption that light propagation is fully unaffected by its motion wrt the source.]

Hmmm. What does that mean?

Either:
(1) MMX demonstrates that speed of light relative to the MMX apparatus was the same in every direction.
or
(2) MMX demonstrates that solids undergo Lorentz contraction as they move relative to the frame of reference in which the speed of light is the same in every direction.

That's by far not all:

3) Alternatively if for example transverse light propagation in the ether is reduced by the Lorentz factor by its motion wrt the source, then MMX demonstrates that solids undergo isotropic contraction - I think of that example because it's a proposed theory (by H. Varcollier, 1942 and P. Dive, 1950) that is not compatible with the relativity principle, but still close enough.

That's why we prefer instead of null results, positive evidence of the kind that Michelson was looking for - the kind we already got for the speed of light in moving media (but only well tested along the same direction), and for time dilation.

Cheers,
Harald

 

[harrylin]

So is the only difference that in SR we decide not to care that "we don't know where the ether rest frame is."

Even stronger: SR does not care if an ether exists. On purpose an ether is not part of its postulates and it's not required for the (re)derivation of the Lorentz transformations. So, the physical model is replaced by a set of rules. And if one still wants to make intuitive or physical sense of it, then one may use for example the stationary ether model or, alternatively, a physical interpretation of Minkowski Spacetime.

However, IMHO that is cheating a little, as the light postulate summarizes the consequences of the stationary ether model.

 

[thwle]

That's by far not all:

3) Alternatively if for example transverse light propagation in the ether is reduced by the Lorentz factor by its motion wrt the source, then MMX demonstrates that solids undergo isotropic contraction - I think of that example because it's a proposed theory (by H. Varcollier, 1942 and P. Dive, 1950) that is not compatible with the relativity principle, but still close enough.

That's why we prefer instead of null results, positive evidence of the kind that Michelson was looking for - the kind we already got for the speed of light in moving media (but only well tested along the same direction), and for time dilation.

Cheers,
Harald

I have to suppose you understand what your said. Have you understood the things I have said?

Admitting my uncertainty as to the meaning of the bold (above), I suppose many other interpretations are possible if enough new postulates be accepted to cobble a correspondence. If one honors Occam's principle, I maintain that only the two possibilities are available. I think we agree the first of the two can be ruled out based on evidence external to MMX. I daresay, they are logically an exhaustion of possibility.

Please tell me what you think of my reasoning in my previous post (here quoted):

"I also think the equivalence [of radar ranging and measuring stick measuring] stands to reason: If the forces between atoms in a solid are communicated at the speed of light, then they would be equivalent. Only if the forces were instantaneously communicated would they be different as calculated by Michelson and Morley."

Think of a Hydrogen molecule. What communication of forces between the two hydrogen atoms determines the distance between them? What is the speed of that communication and relative to what frame of reference is that speed? Isn't this interaction between atoms rather like echo ranging?

 

[ghwellsjr]

... [two] theories:

In one of these, Lorentz Ether Theory (LET), it is postulated that there exists only a single absolute frame of reference in which light actually travels in all directions at the speed c and only when you are at rest in that frame will your measurements reflect what is really happening. All other inertially moving observers get the same results because nature is playing tricks on them by adjusting their clocks and rulers in such a way that they get the same results as they would get if they were stationary in the ether. In fact, since we don't know where the ether rest frame is, chances are, all observers are not at rest in the ether frame and so it's a safe bet that we all have our clocks and rulers modified.

Special Relativity, SR, on the other hand, postulates that you can consider anyone of the inertial observers to be at rest in the ether frame of reference where his measurements reflect what is really going on and all the other inertially moving observers are getting their clocks and rulers modified by nature in such a way that they get the same result as they would if they were at rest in the ether but the theory says that their clocks and rulers are actually getting modified, according to the one observer which we are considering to be at rest in the ether.

So is the only difference that in SR we decide not to care that "we don't know where the ether rest frame is."

Actually, I like harrylin's suggested alternative to my second paragraph quoted above where he basically substituted the word "pretend":

Special Relativity postulates that you can pretend anyone of the inertial observers to be at rest in the ether frame of reference so that all the other inertially moving observers are getting their clocks and rulers modified by nature in such a way that they get the same result as they would if they were at rest in the ether; the theory thus says that - according to the one observer which we are considering to be at rest in the ether - their clocks and rulers are actually affected by their motion.
And just as in Newtonian mechanics, any observer can pretend to be in rest so that it's the others that move - but if we pretend all to be at rest at the same time then we mess up!

So it's not so much that "we decide not to care", it's that we can pretend that any inertial reference frame will behave exactly like the illusive ether frame. It's so much easier to do science this way than to be concerned about where that pesky ether resides.

 

[ghwellsjr]

...
Please tell me what you think of my reasoning in my previous post (here quoted):

"I also think the equivalence [of radar ranging and measuring stick measuring] stands to reason: If the forces between atoms in a solid are communicated at the speed of light, then they would be equivalent. Only if the forces were instantaneously communicated would they be different as calculated by Michelson and Morley."

Think of a Hydrogen molecule. What communication of forces between the two hydrogen atoms determines the distance between them? What is the speed of that communication and relative to what frame of reference is that speed? Isn't this interaction between atoms rather like echo ranging?

I came across this passage from Hermann Bondi's book, Relativity and Common Sense:

"THE VELOCITY OF LIGHT
On this basis, then, we can look at time standards as primary and at distance standards as quite secondary and of little importance. This does seem to be a sound procedure, particularly when we think about what our inch tapes and measuring rods are actually made of. We know that they are composed of atoms whose structure is kept in shape by electric forces. We know that these atoms have certain periods of vibration and we know that, in the materials we call very rigid, it is as a consequence of the particular periods of vibration of the atoms that different atoms keep a definite distance apart in the structure of the rod. Thus we can argue that the length of a rod is really determined by the period of the oscillation of the atoms of which it is composed, this being translated, in the usual way, through the velocity of light into distance. If we argue, as we well may, that the distances between the atoms in what we call rigid materials are the distances corresponding to the oscillations of the atoms, then we could say that those distances, too, are effectively determined by radar methods. On that basis, then, distance becomes a purely secondary quantity, time is the primary thing, and the velocity of light is in natural units necessarily equal to unity. But if we are so perverse as to choose to measure distances in feet rather than in light millimicroseconds, then we have to introduce a conventional factor of conversion which effectively defines the foot, and this we call the velocity of light."

He was not discussing length contraction at this time but his argument seems to be applicable to what you are suggesting.

However, I don't think too many scientists these days concern themselves with the mechanism of length contraction, I believe they are content to regard it as a natural consequence of Special Relativity.

 

[ghwellsjr]

...
Either:
(1) MMX demonstrates that speed of light relative to the MMX apparatus was the same in every direction.
or
(2) MMX demonstrates that solids undergo Lorentz contraction as they move relative to the frame of reference in which the speed of light is the same in every direction.

As I see it, Lorentz took interpretation (2) because he assumed an absolute ether rest frame in which MMX was not at rest while Einstein took interpretation (1) if he assumed a reference frame in which MMX was at rest or (2) if he assumed a reference frame in which MMX was not at rest (one in which the sun is at rest, for example, or any other candidate for the presummed ether).

As harrylin pointed out here:

Einstein put it as follows:

"for a co-ordinate system moving with the Earth the mirror system of Michelson and Morley is not shortened, but it is shortened for a co-ordinate system which is at rest relatively to the sun."
- http://www.bartleby.com/173/16.html

 

[harrylin]

I have to suppose you understand what your said. Have you understood the things I have said?

Yes and yes; and from your reply it appears that you still did not understand what I said. See next.

Admitting my uncertainty as to the meaning of the bold (above), I suppose many other interpretations are possible if enough new postulates be accepted to cobble a correspondence. If one honors Occam's principle, I maintain that only the two possibilities are available. I think we agree the first of the two can be ruled out based on evidence external to MMX. I daresay, they are logically an exhaustion of possibility.

My reply was to your argument which did not include Occam's razor; obviously the two first two options are not exhaustive but sure they are the simplest. Similarly Michelson based his reasoning on a number of unmentioned assumptions, using Occam's principle. And he was wrong. The evidence forced people to correct his reasoning by a new postulate, be it Lorentz contraction or the PoR. New evidence can force us to again modify our assumptions. If I'm not mistaken, Voigt even derived the third possibility from the wave equation and I have never seen a rebuttal. As I know of such options in the literature, I cannot agree that your two simplest options are "logically an exhaustion of possibility".

Please tell me what you think of my reasoning in my previous post (here quoted):

"I also think the equivalence [of radar ranging and measuring stick measuring] stands to reason: If the forces between atoms in a solid are communicated at the speed of light, then they would be equivalent. Only if the forces were instantaneously communicated would they be different as calculated by Michelson and Morley."

Think of a Hydrogen molecule. What communication of forces between the two hydrogen atoms determines the distance between them? What is the speed of that communication and relative to what frame of reference is that speed? Isn't this interaction between atoms rather like echo ranging?

Already twice I replied with yes to that! ;-)

Also Einstein admitted on the page I cited earlier that "The special theory of relativity has crystallised out from the Maxwell-Lorentz theory of electromagnetic phenomena".

 

[Buckleymanor]

"I also think the equivalence [of radar ranging and measuring stick measuring] stands to reason: If the forces between atoms in a solid are communicated at the speed of light, then they would be equivalent. Only if the forces were instantaneously communicated would they be different as calculated by Michelson and Morley."

Think of a Hydrogen molecule. What communication of forces between the two hydrogen atoms determines the distance between them? What is the speed of that communication and relative to what frame of reference is that speed? Isn't this interaction between atoms rather like echo ranging?

They would allso be different if the forces interacted slower than the speed of light.
It's hard to imagine that all materials irrespective of there mass would expand or contract at the same speed , the speed of light.
Gravitational effects upon the mass in those different materials would prevent this.

 

[roineust]

Thanks ghwellsjr,
One more pre exercise question...sorry, for asking questions indeed I don't need to prepare time in advance.

What is the relation between the current understanding of time dilation and clock synchronization? What I mean is this - If I make many times an experiment that shows me that 10 'ticks' of clock 1 (say a very precise clock etc...) are never the same as 10 'ticks' of an identical clock 2, because they are at different inertial frames - Then why can't I take these results and formalize them in such a way that I say: If there is inertial difference, 10 ticks of no.1 will never be the same as 10 ticks of no.2, and it has nothing to do with synchronization (although the results were achieved using synchronization).


Thanks,
Roi.

 

[thwle]

They would allso be different if the forces interacted slower than the speed of light.
It's hard to imagine that all materials irrespective of there mass would expand or contract at the same speed , the speed of light.
Gravitational effects upon the mass in those different materials would prevent this.

The amount of contraction would depend in the speed of communication of the forces that govern the dimensions. Instantaneous for no contraction (as assumed in MMX). I said nothing about speed of contraction.

 

[thwle]

Yes and yes; and from your reply it appears that you still did not understand what I said.

Yes, I admit that I don't. Not that I don't agree; I just can't make out what you mean.

... New evidence can force us to again modify our assumptions.

With my next post I will present new evidence showing that it is possible (1) to recognize the inertial frame of reference in which light propagates at the same speed in all directions and (2) to discover inertial frames in which it does not.

 

[harrylin]

As I see it, Lorentz took interpretation (2) because he assumed an absolute ether rest frame in which MMX was not at rest while Einstein took interpretation (1) if he assumed a reference frame in which MMX was at rest or (2) if he assumed a reference frame in which MMX was not at rest (one in which the sun is at rest, for example, or any other candidate for the presummed ether).

As harrylin pointed out here:

Thanks ghwellsjr,
One more pre exercise question...sorry, for asking questions indeed I don't need to prepare time in advance.

What is the relation between the current understanding of time dilation and clock synchronization? What I mean is this - If I make many times an experiment that shows me that 10 'ticks' of clock 1 (say a very precise clock etc...) are never the same as 10 'ticks' of an identical clock 2, because they are at different inertial frames - Then why can't I take these results and formalize them in such a way that I say: If there is inertial difference, 10 ticks of no.1 will never be the same as 10 ticks of no.2, and it has nothing to do with synchronization (although the results were achieved using synchronization).

Thanks,
Roi.

Hi Roi, it's not clear to me what you want to do, and how it relates to the topic... I agree that there is a fundamental difference, as clock synchronization is a human choice while time dilation relates to a physical phenomenon that also manifests itself for cases in which clock synchronization plays no role.
However, for inertial motion the two are interrelated. That is because if you want to measure the time between two ticks of a clock that is moving past your clocks, you need two synchronized clocks to do that. Alternatively, with only one clock, you can film the moving clock from a distance, but the correction for the propagation time is related to the clock synchronization which is simply based on a convenient speed of light assumption. So, although it implies a different speed of light in different directions wrt your frame, you can always adapt your measurement such that 10 ticks of no.1 will be (or appear to be) the same as 10 ticks of no.2. Does that help?

Harald

 

[Buckleymanor]

The amount of contraction would depend in the speed of communication of the forces that govern the dimensions. Instantaneous for no contraction (as assumed in MMX). I said nothing about speed of contraction.

Well I don't understand what you are talking about, you mentioned.

Think of a Hydrogen molecule. What communication of forces between the two hydrogen atoms determines the distance between them?

Contraction is not specificaly mentioned then what is it you are you trying to communicate.

 

[harrylin]

Hello all and Buckleymanor, for understanding the Fitzgerald contraction it can be enlightening to check out the paper which probably gave him that idea. You can find it here:

http://en.wikisource.org/wiki/Motion_of_Electrification_through_a_Dielectric

Note in particular the section on "Complete Solution ..." and eq.29.

 

[thwle]

harrylin wrote: "It's an indirect demonstration of Lorentz contraction - based on our assumption that light propagation is fully unaffected by its motion wrt the source.]

thwle replied: "Hmmm. What does that mean?" [Because thwle doesn't understand the difference between motion of light and propagation of light.]

thwle also wrote:
"Either:
(1) MMX demonstrates that speed of light relative to the MMX apparatus was the same in every direction.
or
(2) MMX demonstrates that solids undergo Lorentz contraction as they move relative to the frame of reference in which the speed of light is the same in every direction. "
[Because MMX involves no clocks thwle thinks time dilation arguments are irrelevant and that contraction is all that remains to explain the null result.]

harrylin's claimed he understood thwle, but thwle continued to doubt that harrylin did -- or that Buckleymaster did -- though ghwellsjr clearly understood thwle at least in part after at first resisting and finally expressed surprise that he had been unable to see thwle's point sooner.

thwle got to feeling a little frustrated and rashly promised to demonstrate that a unique frame or reference in which light proagates at the same speed in all directions not only exists but is discernable from other frames of reference.

Now, thwle has had the audacity to perform on his promise: See the new thread "Absolute Rest" under special and general relativity.

 

[thwle]

harrylin wrote: "It's an indirect demonstration of Lorentz contraction - based on our assumption that light propagation is fully unaffected by its motion wrt the source.]

thwle replied: "Hmmm. What does that mean?" [Because thwle doesn't understand the difference between motion of light and propagation of light.]

thwle also wrote:
"Either:
(1) MMX demonstrates that speed of light relative to the MMX apparatus was the same in every direction.
or
(2) MMX demonstrates that solids undergo Lorentz contraction as they move relative to the frame of reference in which the speed of light is the same in every direction. "
[Because MMX involves no clocks, thwle thinks time dilation arguments are irrelevant and that contraction is all that remains to explain the null result.]

harrylin claimed he understood thwle, but thwle continued to doubt that harrylin did -- or that Buckleymaster did -- though ghwellsjr clearly understood thwle at least in part (after at first resisting) and finally expressed surprise that he had been unable to see thwle's point sooner.

thwle got to feeling a little frustrated and rashly promised to demonstrate that a unique frame or reference in which light proagates at the same speed in all directions not only exists but is discernable from other frames of reference.

Now, thwle has had the audacity to perform on his promise: See the new thread "Absolute Rest" under special and general relativity.

 

[Dale]

But thwle is wrong in his analysis.

 

[PhilDSP]

Hello thwle, I'd like to add some comments.

Either:
(1) MMX demonstrates that speed of light relative to the MMX apparatus was the same in every direction.
or
(2) MMX demonstrates that solids undergo Lorentz contraction as they move relative to the frame of reference in which the speed of light is the same in every direction.

As I think Harald implied, it might be on pretty shaky logical ground to make very limiting inferences from a null result. My take on your point (1) for instance is that really, what was demonstrated was that the apparent phase of the light wave was the same in every direction. There are additional steps required to actually prove that the apparent velocity was the same. (I'm thinking in terms of Wave Mechanics here)

Please tell me what you think of my reasoning in my previous post (here quoted):

"I also think the equivalence [of radar ranging and measuring stick measuring] stands to reason: If the forces between atoms in a solid are communicated at the speed of light, then they would be equivalent. Only if the forces were instantaneously communicated would they be different as calculated by Michelson and Morley."

Think of a Hydrogen molecule. What communication of forces between the two hydrogen atoms determines the distance between them? What is the speed of that communication and relative to what frame of reference is that speed? Isn't this interaction between atoms rather like echo ranging?

We should remember that any medium apart from a pure vacuum is dispersive. That means the effective speed of EM propagation is slowed compared with c. So any inter-atom and inter-molecule force changes are not in step with light propagation and are different for each piece of the MMX apparatus.

 

[thwle]

But thwle is wrong in his analysis.

Can you be specific?

 

[thwle]

Hello thwle, I'd like to add some comments.



As I think Harald implied, it might be on pretty shaky logical ground to make very limiting inferences from a null result. My take on your point (1) for instance is that really, what was demonstrated was that the apparent phase of the light wave was the same in every direction. There are additional steps required to actually prove that the apparent velocity was the same. (I'm thinking in terms of Wave Mechanics here)

The phase going in was the same (at the half-silvered mirror beam-splitter). The phase coming out remained the same before during and after rotation. Necessary conclusion the path lengths in wavelengths could not have changed except by the same number of wavelengths. The path lengths had been set up "equal" (within a few tenths of a millimeter), so it remains uncertain whether the number of wavelengths along the paths was unchanged or did change. I tend to believe the path lengths in wavelengths was constant.

We should remember that any medium apart from a pure vacuum is dispersive. That means the effective speed of EM propagation is slowed compared with c. So any inter-atom and inter-molecule force changes are not in step with light propagation and are different for each piece of the MMX apparatus.

Do you think "dispersive medium" is an appropriate description of interatomic spaces within molecules?