The aether was a flawed experiment?

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Discussion Overview

The discussion revolves around the Michelson-Morley experiment and its implications regarding the aether theory and the speed of light. Participants explore the nature of light as a perturbation of aether, the effects of movement through aether, and the experiment's ability to measure light's speed under various conditions. The conversation includes technical reasoning, conceptual clarifications, and references to historical theories.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Historical

Main Points Raised

  • Some participants propose that if light behaves like sound waves in a medium, its speed should be independent of aether flow, while others argue that it should depend on the observer's movement through aether.
  • There is a discussion about how wind affects sound waves, with some participants asserting that sound waves are indeed affected by air movement, which raises questions about the analogy with light.
  • Participants question how much aether speed would need to be to significantly affect electromagnetic waves, with references to the Earth's rotation speed.
  • Some participants note that the Michelson-Morley experiment was designed to measure phase differences between light waves, which could indicate variations in light speed.
  • There is a claim that the Michelson-Morley experiment does not prove a constant speed of light, with references to other experiments like the Kennedy-Thorndike experiment that also aim to address this issue.
  • Participants express differing beliefs about the necessity of experiments to prove the constancy of light speed, with some asserting confidence in Maxwell's equations while others remain skeptical of the conclusions drawn from the Michelson-Morley experiment.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the implications of the Michelson-Morley experiment and the nature of light. There is no consensus on whether the experiment proves a constant speed of light or adequately addresses the aether theory.

Contextual Notes

Participants highlight the sensitivity of measuring apparatuses and the conditions under which the Michelson-Morley experiment was conducted, noting that modern devices have improved sensitivity. There are unresolved questions about the absolute motion of inertial frames and the implications of various theories on light propagation.

crx
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OK, i imagine that a few ensteiniens of you will roll eyes when they hear...aether! I was thinking about Michelson-Morley experiment and i have some questions. If light is thought to be an perturbation of aether (just like waves on water or sound waves) that their speed should be independent of any aether flow (in case that we suppose that Earth is moving through aether, i guess), just like sound waves, their direction and speed its independent of the air movement. So the experiment i guess was not adequate to show any result...
 
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crx said:
If light is thought to be an perturbation of aether (just like waves on water or sound waves) that their speed should be independent of any aether flow
But not independent of our movement through it.
If there is a fixed aether with a fixed speed of light relative to it we should see a different speed moving in opposite directions - exactly the same as the doppler effect
 
crx said:
just like sound waves, their direction and speed its independent of the air movement.
But the direction and speed of sound waves are not independent of the air movement. If this were not the case then it would be very difficult for passengers on a jet to carry on a conversation.
 
DaleSpam said:
But the direction and speed of sound waves are not independent of the air movement. If this were not the case then it would be very difficult for passengers on a jet to carry on a conversation.

So if i shoot a focused ultrasound to a target (transducer), in no moving air i will miss the target when the air between the source and target its blowing? I think yes, if the speed of the wind its considerable high relative to the speed of the sound and the source...But how much should be the aether speed (relative to the source) to have a considerable effect on an electromagnetic wave?
 
crx said:
So if i shoot a focused ultrasound to a target (transducer), in no moving air i will miss the target when the air between the source and target its blowing? I think yes, if the speed of the wind its considerable high relative to the speed of the sound and the source...
Yes. As a matter of fact, this very technique is used to noninvasively measure the speed of water in pipes.
...But how much should be the aether speed (relative to the source) to have a considerable effect on an electromagnetic wave?
Well, the speed due to the Earth's rotation is about 1000mph -- and that's enough we should be able to detect it.
 
crx said:
But how much should be the aether speed (relative to the source) to have a considerable effect on an electromagnetic wave?
That all depends on the sensitivity of your measuring apparatus. That was the whole point of the Michelson-Morley experiment. They had built a very sensitive device. Modern devices are much more sensitive, on the order of 2 cm/s or better.
 
DaleSpam said:
That all depends on the sensitivity of your measuring apparatus. That was the whole point of the Michelson-Morley experiment. They had built a very sensitive device. Modern devices are much more sensitive, on the order of 2 cm/s or better.

what do they measure?
 
cfrogue said:
what do they measure?

the phase difference between the two waves...interferometer
 
crx said:
the phase difference between the two waves...interferometer

Oh, so this does not measure the contant speed of light?
 
  • #10
cfrogue said:
Oh, so this does not measure the contant speed of light?
Yes it does, the device is constructed so that if the speed of light is not constant any difference shows up in the phase.
 
  • #11
cfrogue said:
Oh, so this does not measure the contant speed of light?

It compares the relative speed of light in the two arms - very accurately!
 
  • #12
mgb_phys said:
It compares the relative speed of light in the two arms - very accurately!

Frequency is a function of wavelength and speed. MMX measures frequency.

To decide that speed has been detemined, one would have to know the absolute motion of an inertial frame to eliminate the wavelength compression as a determining factor.

Modern Physics/Michelson-Morley Experiment
Walter Ritz's emitter theory (or ballistic theory), was also consistent with the results of the experiment
http://en.wikibooks.org/wiki/Modern_Physics:Michelson-Morley_Experiment



This rules out any conceptually coherent ballistic theory of light propagation, according to which the speed of light is the vector sum of the velocity of the source plus a vector of magnitude c. Ironically, the original Michelson-Morley experiment was consistent with the ballistic theory, but inconsistent with the naïve ether theory, whereas the Sagnac effect is consistent with the naïve ether theory but inconsistent with the ballistic theory. Of course, both results are consistent with fully relativistic theories of Lorentz and Einstein, since according to both theories light is propagated at a speed independent of the state of motion of the source.
http://www.mathpages.com/rr/s2-07/2-07.htm

Walter Ritz's emitter theory (or ballistic theory), was also consistent with the results of the experiment, not requiring aether. The theory postulates that light has always the same velocity in respect to the source.[6] However it also led to several "obvious" optical effects that were not seen in astronomical photographs, notably in observations of binary stars in which the light from the two stars could be measured in an interferometer. If this was correct, the light from the stars should cause fringe shifting due to the velocity of the stars being added to the speed of the light, but again, no such effect could be seen.
http://en.wikipedia.org/wiki/Michelson-Morley_experiment

Here is the bottom line, MMX does not prove a constant speed of light.

That is why in the early 60's, some folks began to try to eliminate Ritz's theory with experiments from moving light sources since MMX could not do that.
http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html#moving-source_tests
 
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  • #13
cfrogue said:
Here is the bottom line, MMX does not prove a constant speed of light.
True - but do you need an experiment to prove the speed of light is constant.
Don't you believe Maxwell ?
 
  • #14
DaleSpam said:
Yes it does, the device is constructed so that if the speed of light is not constant any difference shows up in the phase.

what about the Sagnac effect ?
 
  • #15
mgb_phys said:
True - but do you need an experiment to prove the speed of light is constant.
Don't you believe Maxwell ?

I absolutely believe the speed of light is a constant.
I just understand MMX does not prove it.


This is further proof, MMX cannot measure speed.

The Kennedy-Thorndike Experiment
R.J. Kennedy and E.M. Thorndike, “Experimental Establishment of the Relativity of Time”, Phys. Rev. 42 400–418 (1932).
This uses an interferometer similar to Michelson's, except that its arms are of different length, and are not at right angles to each other. They used a spectacular technique to keep the apparatus temperature constant to 0.001°C, which gave them sufficient stability to permit observations during several seasons. They also used photographs of their fringes (rather than observing them in real time as in most other interferometer experiments). Their apparatus was fixed to the Earth and could only rotate with it. Their null result is consistent with SR.
 
  • #16
crx said:
what about the Sagnac effect ?

what about it.

I understand it.
 
  • #17
cfrogue said:
I absolutely believe the speed of light is a constant.
You shouldn't believe it absolutely! :bugeye:

This is further proof, MMX cannot measure speed.
It never claimed to.
 
  • #18
Hurkyl said:
You shouldn't believe it absolutely! :bugeye:

Yes, I should.

What are the choices.

I know all of them.

It is the case, that most of physics accepts mindless detail on this matter.

I wonder what you do.

Hurkyl said:
It never claimed to.

Yes, most of physics falsely claims MMX proves a constant speed of light.
 
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  • #19
cfrogue, you are more or less correct, although I think you are exagerating. MMX and similar interferometer experiments prove isotropy of the speed of light. This is part of the speed of light being "constant" but certainly not all of it. Other experiments were required and performed. That is why the FAQ has more than one entry.
 
  • #20
mgb_phys said:
do you need an experiment to prove the speed of light is constant.
Don't you believe Maxwell?

Even if you believe Maxwell, don't you need to check to the precision that technology allows that he was right?
 
  • #21
cfrogue said:
What are the choices.
How about having a belief conditioned on available evidence?

Yes, most of physics falsely claims MMX proves a constant speed of light.
Earlier, you were talking about whether MMX measures the speed of light. Now you're talking about whether MMX proves the speed of light is constant. Make up your mind.
 
  • #22
Hurkyl said:
How about having a belief conditioned on available evidence?

Good idea.
The available evidence of a constant light speed from moving light sources plus MMX, points strongly in the direction that the speed of light is a constant.


Hurkyl said:
Earlier, you were talking about whether MMX measures the speed of light. Now you're talking about whether MMX proves the speed of light is constant. Make up your mind.
If I talked about MMX measuring the speed of light, then my wording was wrong.

I would never claim MMX can measure the speed of light.

Nor, would I claim MMX proves a constant speed of light either.

The tests of light speed from moving light sources show the speed of light cannot be speed injected with the motion of the light source.
These eliminate Ritz's emission theory. The results of Sagnac are also inconsistent with light emission theory.
 

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