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

[thwle]

Where did you get the idea that anybody made the assumption that any two methods for measuring distance would yield different results?

That IS the MMX.

 

[ghwellsjr]

That IS the MMX.

I suppose your linked paper makes that claim? I tried to understand that paper but gave up. Can you point to a specific quote to support the idea that anybody believed that two different methods to measure a distance would produce different results?

 

[Buckleymanor]

Beg pardon! There is a difference between comparing light phase and comparing light speed.

There was neither comparison nor measure of light speed in MMX.

As you allready stated.

OK. If there had been a phase shift, a time difference could have been inferred.

I can't see why the assumption from this can't be drawn,(there was no phase shift) that the speed of light at the observation point is the same, irrespective of it's speed.
Though you go on to state.

There was not and would not have been even if frequency changed.

Which I am not quite sure about what you are saying.

 

[Dale]

Question: Why at the end of page 378, and at the beginning of page 379, the writer claims: " ...The fundamental measurement of one kind of interval is not to be reduced to that of the other with the aid of postulated constancy of the velocity of light, as would for example..." - Without naming the reason for that restriction...?

He actually did mention the reason for the restriction, but it was rather subtle. In the introduction Robertson said that he wanted to determine "the degree to which postulate can now be replaced by observation". So he could not use light-clocks since those rely on the second postulate.

 

[Dale]

Is this paper concerned with both of Einstein's postulates or just the first one?

Both. By using the form of the metric ds² = -g0²c²dt² + g1²dx² + g2²(dy² + dz²) Robertson is not assuming either postulate.

Instead he is making a general theory without those postulates and then simply looking to experiments to set the undetermined parameters of the metric (or equivalently the coordinate transformation).

 

[TrickyDicky]

If the interpretation of Lorentz of the MMX were correct (that the experiment frame was moving wrt the ether absolute rest frame and it was experiencing length contraction and time dilation), it would indeed prevent any experiment from succeding measuring a different speed of light than c regardless the motion of the light source (that is actually the case, to this day no experiment has been able to falsify this claim of special relativity). In this sense Einstein and Lorentz interpretation would reach the same predictions and by Ocam's razor the ether would be superfluous.

But could another approach be used to solve this, since measuring the speed of light seems a dead end, perhaps measuring the doppler shift of the Earth with respect to the vacuum?

 

[thwle]

As you allready stated.

I can't see why the assumption from this that the speed of light at the observation point is the same irrespective of it's speed.
Though you go on to state.

Which I am not quite sure about what you are saying.

What! ?

Let me try again: MMX consists of
(1) a rotatable stone slab on which two orthogonal folded paths are laid out, (two measuring sticks.)
(2) a light source ("argand lamp")
(3) a half silvered mirror at the common endpoint of the two paths to split and recombine the light beam at the beginning and end, respectively, of the round trip along each path.
(4) a telescope to observe the interference pattern in the recombined beam.

(2), (3) and (4) constitute a radar ranging measurement of the measuring sticks, except that rather than a count of wavelengths along the two paths only a count of differences between the two paths is observed. That being zero. It appears that the two methods of length measurment may be equivalent.

I conjecture that the dimensions of a material measuring stick, being dependent on the spacing of its atomic constituents, is dependent upon the forces between those constituents, which (if the forces be propagated or communicated between atoms at light speed) would always establish spacing determined (in effect) by radar ranging.

I hope this clears things up.

thwle

 

[lugita15]

My point is that if Maxwell had the foresight of Einstein's hindsight, he would not have proposed an experiment to measure the speed of the surface of the Earth through the absolute stationary ether because he would have realized that his equations predicted that it was unmeasureable.

I would disagree with that. I don't think Maxwell would have considered it significant that there exists a set of transformations which leave his equations unchanged. In fact, the whole reason he proposed experiments to measure the motion of the aether is because he believed that the aether frame was the only frame in which his equations were exactly correct.

 

[ghwellsjr]

Both. By using the form of the metric ds² = -g0²c²dt² + g1²dx² + g2²(dy² + dz²) Robertson is not assuming either postulate.

Instead he is making a general theory without those postulates and then simply looking to experiments to set the undetermined parameters of the metric (or equivalently the coordinate transformation).

Did I misunderstand the purpose of the paper? I thought it was to change the nature of the first postulate so that it was backed up by experimental evidence and no longer just an unsupported postulate.

 

[ghwellsjr]

That IS the MMX.

I suppose your linked paper makes that claim? I tried to understand that paper but gave up. Can you point to a specific quote to support the idea that anybody believed that two different methods to measure a distance would produce different results?

I must appologize here. You did not provide a link to a paper. I did a search on "emmision theory" earlier and found a paper that I thought you had linked to. Sorry.

But I'm still wondering where you got the idea that anybody at the time of MMX thought that two different ways of measuring a distance would give two different results. Can you provide some evidence for that?

Here is a post of yours:

They expected to demonstrate further against emission theory by detecting the velocity of the Earth, but that depended on assumptions that light traveled at a fixed speed relative to a frame of reference (ether) and (unstated) that measuring stick length is not equivalent to radar ranging (not by that name, of course.)

Here you say that they did not state that they believed that the two methods of measuring length were not equivalent, so if they didn't state it, why do you think they believed it?

And then there's this post:

MMX consists of
(1) a rotatable stone slab on which two orthogonal folded paths are laid out, (two measuring sticks.)
(2) a light source ("argand lamp")
(3) a half silvered mirror at the common endpoint of the two paths to split and recombine the light beam at the beginning and end, respectively, of the round trip along each path.
(4) a telescope to observe the interference pattern in the recombined beam.

(2), (3) and (4) constitute a radar ranging measurement of the measuring sticks, except that rather than a count of wavelengths along the two paths only a count of differences between the two paths is observed. That being zero. It appears that the two methods of length measurment may be equivalent.

What non-null result do you think Michelson and Morley expected?

 

[ghwellsjr]

If the interpretation of Lorentz of the MMX were correct (that the experiment frame was moving wrt the ether absolute rest frame and it was experiencing length contraction and time dilation), it would indeed prevent any experiment from succeding measuring a different speed of light than c regardless the motion of the light source (that is actually the case, to this day no experiment has been able to falsify this claim of special relativity). In this sense Einstein and Lorentz interpretation would reach the same predictions and by Ocam's razor the ether would be superfluous.

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.

But could another approach be used to solve this, since measuring the speed of light seems a dead end, perhaps measuring the doppler shift of the Earth with respect to the vacuum?

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

 

[ghwellsjr]

My point is that if Maxwell had the foresight of Einstein's hindsight, he would not have proposed an experiment to measure the speed of the surface of the Earth through the absolute stationary ether because he would have realized that his equations predicted that it was unmeasureable. But I'm not complaining, Maxwell was the most brilliant scientist of the 19th century in my opinion and hindsight is always better than foresight.

I would disagree with that. I don't think Maxwell would have considered it significant that there exists a set of transformations which leave his equations unchanged. In fact, the whole reason he proposed experiments to measure the motion of the aether is because he believed that the aether frame was the only frame in which his equations were exactly correct.

I totally agree with your last sentence but it is at odds with the sentence before it because the Lorentz Transform is how we determine that if a set of equations is correct in one frame, it is correct in all frames. Of course, I'm assuming that Maxwell would have known the significance of the transform.

 

[Born2bwire]

I totally agree with your last sentence but it is at odds with the sentence before it because the Lorentz Transform is how we determine that if a set of equations is correct in one frame, it is correct in all frames. Of course, I'm assuming that Maxwell would have known the significance of the transform.

It's significant to note that Maxwell only lived for another 15 years after he published his treatise (dying in the late 1870's). His original work was very complicated and used cumbersome quarternions. It wasn't until after his death that the field theory and the classic four equations were derived. In addition, experimental work on electromagnetic waves (other than light) did not really take off until after his death as well. Hertz did his famous experiments in the 1880's. Really, I would say that the 1880's is one of the big decades for electromagnetics because that was the decade where electromagnetic experimentation really started and we begin to see the empirical proof of Maxwell's Equations for electromagnetic waves. In the following decade of the 1890's, Lorentz, Poincare and others developed the Lorentz Transformations and then it was in the early or mid 1900's that Einstein published his work.

So given the historical context I do not think one would think any less of James Clerk Maxwell for missing these things since he did not live long enough to see theorists really flesh out his work and for experimentalists catch up with his theories.

 

[ghwellsjr]

So given the historical context I do not think one would think any less of James Clerk Maxwell for missing these things since he did not live long enough to see theorists really flesh out his work and for experimentalists catch up with his theories.

Thanks for that additional historical context and I agree with what you say about Maxwell as I pointed out earlier here:

My point is that if Maxwell had the foresight of Einstein's hindsight, he would not have proposed an experiment to measure the speed of the surface of the Earth through the absolute stationary ether because he would have realized that his equations predicted that it was unmeasureable. But I'm not complaining, Maxwell was the most brilliant scientist of the 19th century in my opinion and hindsight is always better than foresight.

 

[Dale]

Did I misunderstand the purpose of the paper? I thought it was to change the nature of the first postulate so that it was backed up by experimental evidence and no longer just an unsupported postulate.

Not exactly. He just scrapped both postulates, made a completely general theory, and checked to see what restrictions experiments placed on the parameters of the general theory.

 

[TrickyDicky]

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

Noone seriously would want to abandon SR in its restricted range of application, that's why is called "special" or "restricted" relativity. But we all know we don't live in a "special relativity" world, ours is not Minkowski spacetime.
And some physicists (such as Nobel winner Bob Laughlin in his book "A different universe" in a chapter called The Fabric of Spacetime) claim that in a way Einstein re-introduced a form of ether with GR or the concept of empty space as a medium or substance.
It has also been said here that Maxwell believed that the ether frame was the only frame in which his equations were exactly correct. If we follow Lorentz here this would mean that the ether frame, that is the absolute rest frame, is the only frame where his tranformations hold exactly.

 

[thwle]

I'm still wondering where you got the idea that anybody at the time of MMX thought that two different ways of measuring a distance would give two different results. Can you provide some evidence for that?

The evidence is that the null result is the necessary conseqence of the equivalence and they didn't expect the null result.

 

[thwle]

What non-null result do you think Michelson and Morley expected?

They expected the interference pattern to shift.

 

[ghwellsjr]

Noone seriously would want to abandon SR in its restricted range of application, that's why is called "special" or "restricted" relativity. But we all know we don't live in a "special relativity" world, ours is not Minkowski spacetime.

I didn't know that. I thought I lived in a special relativity world. But if what you are saying is that we don't live in just a special relativity world, we also live in a general relativity world, then I would agree with you.

And some physicists (such as Nobel winner Bob Laughlin in his book "A different universe" in a chapter called The Fabric of Spacetime) claim that in a way Einstein re-introduced a form of ether with GR or the concept of empty space as a medium or substance.

I don't believe anything in GR provides for an absolute ether rest frame.

It has also been said here that Maxwell believed that the ether frame was the only frame in which his equations were exactly correct. If we follow Lorentz here this would mean that the ether frame, that is the absolute rest frame, is the only frame where his tranformations hold exactly.

This doesn't make any sense. The Lorentz Transform is a set of equations that don't know anything about any absolute rest frame. They always "hold" (whatever that means). The issue is whether another set of equations are modified by the LT or remain the same. Maxwell did believe his equations would only work correctly in an absolute rest frame but that has nothing to do with whether or not his equations would come out of the LT in exactly the same form that they went into the LT. Newtonian equations do not come out the same when subjected to the LT so we know they are not frame independent. The fact that Maxwell's equations come out the same means that they apply equally well in any reference frame, not just in an absolute ether rest frame.

 

[Buckleymanor]

What! ?

Let me try again: MMX consists of
(1) a rotatable stone slab on which two orthogonal folded paths are laid out, (two measuring sticks.)
(2) a light source ("argand lamp")
(3) a half silvered mirror at the common endpoint of the two paths to split and recombine the light beam at the beginning and end, respectively, of the round trip along each path.
(4) a telescope to observe the interference pattern in the recombined beam.

(2), (3) and (4) constitute a radar ranging measurement of the measuring sticks, except that rather than a count of wavelengths along the two paths only a count of differences between the two paths is observed. That being zero. It appears that the two methods of length measurment may be equivalent.

I conjecture that the dimensions of a material measuring stick, being dependent on the spacing of its atomic constituents, is dependent upon the forces between those constituents, which (if the forces be propagated or communicated between atoms at light speed) would always establish spacing determined (in effect) by radar ranging.

I hope this clears things up.

thwle

Some, though how do you go about providing evidence of your hypothesis.
It's ok to say the two measurements may be equivalent but if you try to measure one with the other you end up with a null result.
How do you show your stick is longer in one direction to another.

 

[ghwellsjr]

They expected the interference pattern to shift.

But how do you think they expected the interfence pattern to shift? Do you mean it should shift as they rotated the apparatus? Do you mean that it should shift at a constant rate? Do you mean that it shift shift back and forth between two values? Or do you mean that it should only shift as the Earth rotated on its axis and/or revolved around the sun?

 

[TrickyDicky]

I didn't know that. I thought I lived in a special relativity world.

Are you sure? Do we live in a uniform translatory motion universe? According to Einstein's 1905 paper that is the situation in which the first postulate of relativity should rule. Have I read this wrong?

I don't believe anything in GR provides for an absolute ether rest frame.

Ok, but did you read the chapter in the book I mentioned? I think it is in Amazon's preview.

Maxwell did believe his equations would only work correctly in an absolute rest frame but that has nothing to do with whether or not his equations would come out of the LT in exactly the same form that they went into the LT.

I didn't say that. What I said is that if we were to follow Lorentz ether theory, it would make sense that Maxwell equations happen to be Lorentz symmetric, since according to his theory+ the above mentioned Maxwell belief, it is the logical outcome.

 

[thwle]

Some, though how do you go about providing evidence of your hypothesis.
It's ok to say the two measurements may be equivalent but if you try to measure one with the other you end up with a null result.
How do you show your stick is longer in one direction to another.

I don't understand why you say "but", It seems to me "because" would go better -- the null result is the evidence.

Your last sentence baffles me, I have no idea what you mean.

 

[thwle]

But how do you think they expected the interfence pattern to shift? Do you mean it should shift as they rotated the apparatus? Do you mean that it should shift at a constant rate? Do you mean that it shift shift back and forth between two values? Or do you mean that it should only shift as the Earth rotated on its axis and/or revolved around the sun?

On Page 336 (the fourth page of the paper by Michelson and Morley): "If now the whole apparatus be turned through 90 degrees, the difference will be in the opposite direction, hence the displacement of the interference fringes should be 2Dv^2/V^2. ..."

 

[ghwellsjr]

On Page 336 (the fourth page of the paper by Michelson and Morley): "If now the whole apparatus be turned through 90 degrees, the difference will be in the opposite direction, hence the displacement of the interference fringes should be 2Dv^2/V^2. ..."

OK, yes, now I see what you are saying and I agree, they did expect the "radar" method of distance measurement to give a different result than the rod method. In fact, you could say that if they had extremely high precision, they could have done their experiment with just one rod/radar measurement but using two at right angles enables them to get by with less precision. I guess that distinction (two versus one) is what made it difficult for me to see what you were saying but now that I see it, it seems obvious and I can't really understand why I didn't see it the first time you suggested it.

However, I am not agreeing with your statements about emmision theory. I'll post about that later.

 

[thwle]

OK, yes, now I see what you are saying and I agree, they did expect the "radar" method of distance measurement to give a different result than the rod method. ... It seems obvious and I can't really understand why I didn't see it the first time you suggested it.

However, I am not agreeing with your statements about emmision theory. I'll post about that later.

Great!

Honestly, I don't know what to make of emission theory myself. MMX is consistent with it but it raises many questions and I read that other experiments than MMX cast doubt on it.

Thanks

 

[harrylin]

I referred to the paper as I wrote my post.

Yes, emission theory was out of favor, but not disproved. They expected to demonstrate further against emission theory by detecting the velocity of the Earth,

Here you do again not refer to their paper - it's not a coincidence that you don't cite from it (emphasis mine):

"emission theory [..] failed to account for the fact proved by experiment [..].
[...] first, the ether is supposed to be at rest [..] The experimental trial of the first hypothesis forms the subject of the present paper."

but that depended on assumptions that light traveled at a fixed speed relative to a frame of reference (ether) and (unstated) that measuring stick length is not equivalent to radar ranging (not by that name, of course.)
They failed to detect motion of the earth. It seems to me that shows either that emission theory had some truth to it or that there is a greater correspondence of the two methods of length measurement than they had supposed.

See above: emission theory was already disproved. For many people one logical conclusion remained.

Regards,
Harald

 

[harrylin]

If the interpretation of Lorentz of the MMX were correct (that the experiment frame was moving wrt the ether absolute rest frame and it was experiencing length contraction and time dilation), it would indeed prevent any experiment from succeding measuring a different speed of light than c regardless the motion of the light source (that is actually the case, to this day no experiment has been able to falsify this claim of special relativity). In this sense Einstein and Lorentz interpretation would reach the same predictions and by Ocam's razor the ether would be superfluous.

But could another approach be used to solve this, since measuring the speed of light seems a dead end, perhaps measuring the doppler shift of the Earth with respect to the vacuum?

If the theory is right than the PoR cannot be broken, ether or no ether. However:

- Einstein argued in 1920 that the fact that light propagates in space (like a wave) already solved it (a point he had failed to recognize in 1905) and that the properties of space as determined by GRT settled the issue. [Google Einstein ether 1920; he elaborated on that in 1924]

- Ives argued something similar in 1938 when his Doppler experiment established that moving clocks positively suffer retardation by the Lorentz factor due to their speed (a non-null result), which seems to imply the reality of the Lorentz contraction in view of the Kennedy-Thorndyke[sic] experiment. [Google Ives-Stillwell as well as Kennedy-Thorndike]

 

[thwle]

Here you do again not refer to their paper - it's not a coincidence that you don't cite from it (emphasis mine):

"emission theory [..] failed to account for the fact proved by experiment [..].
[...] first, the ether is supposed to be at rest [..] The experimental trial of the first hypothesis forms the subject of the present paper."



See above: emission theory was already disproved. For many people one logical conclusion remained.

Regards,
Harald

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.

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 ... "

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.

 

[roineust]

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.