I am a little surprised by your answer.

M and S appear to be able to say something about the speed of light. To S, the lightning strikes happen the same distance away and light arrives at the same time. So light travels the same speed over the same distance both directions. To M, the lightning strikes happen the same distance away but arrive at different times. This could appear to suggest light did not travel the same speed each way.

But you seem to recognize that within SR, in M's frame, light travels the same speed in either direction. In other words, the train example doesn't exclude SR.

Yes, sure, why would it? It was conceived by Albert Einstein to illustrate the relativity of simultaneity in Special Relativity. It is consistent with Special Relativity since it does nothing other than illustrate what Special Relativity predicts.

OK, so why not take the train and wrap it around a disk so the lightning strikes are next to each other? The lightning strikes are emitters in a Sagnac device. M is the interferometer. In M's frame, the light from different directions arrives at different times. That would appear to make a fringe shift and the Sagnac effect in M's frame.

So if you accept that it's possible to understand M's frame for the train via SR, why couldn't it also be possible to understand M's frame for the Sagnac loop a similar way?

In the train example, Mary, riding the train, observes the two light arrival events at different times. Susan, standing along the tracks, observes the two light arrival events at the same time. That's because Susan is at rest with respect to the locations of light departure and both light signals arrive after t = L / c such that

  t₊ - t_- = L / c - L / c = 0.

In Sagnac's experiment the observer in the loop frame is at rest with respect to the location of light departure. So her name is Susan Sagnac. Like Susan Tracks, Susan Sagnac sees the two light arrival events at the same time:

  t₊ - t_- = L / c - L / c = 0.


Unfortunately for relativists, in reality, as shown by Georges Sagnac, Susan Sagnac sees a fringe shift, showing her that the two light arrival events occur at different times.

Also, there are certain effects that relativity explained, so if you did reject relativity, you would need some other way to explain these effects.

At this point, we are discussing the question whether Special Relativity is falsified by Sagnac's and Wang's experiments. And I don't need to explain any such effects to show that Special Relativity is indeed falsified.

M rev around E

So now you are basically saying "But SR followers say that the theory isn't falsified when it's falsified."

And you're basically saying SR is falsified because an opponent of SR says it's falsified, when it's not.

It's not been my idea to compare Sagnac's experiment and the train example. It's been your idea. Now, after I have shown that the comparison refutes your position, you seem to want to quickly forget it.

If you accuse me of incorrect application of the theory, please substantiate your accusation.

I haven't forgotten the train example at all. And you've agreed already that the train example doesn't refute SR.

You are the one claiming an experiment falsifies a theory. It is your duty to prove that it's a falsification. Part of doing that is to show that you are applying the theory correctly - otherwise you're just falsifying a straw-man.

Sagnac is not a recent experiment. If it were recent, I could understand some debate over interpretation. But SR explained it over a century ago. There were SR explanations of the effect even before Sagnac's experiment. It's not as if nobody ever thought about it before.

Why wouldn't I? Doesn't the mathpages.com author take that for granted too? Don't "most physicists" use mirror interferometers taking that for granted? Didn't you take that for granted when asking for a comparison of the train example and the Sagnac experiment?

Einstein synchronization is a convention for synchronizing clocks at different places by means of signal exchanges. How could that apply to Sagnac's interferometer? Both beams start at one and the same place.

The pulses go in different directions the same distance. Observer M receives these pulses at different times. Does that really sound synchronized from M's perspective?

Why are you asking for the moving frame? Isn't none of the frames special in Special Relativity?

I'm asking about the moving frame because I thought we were talking about the moving frame. Are you talking about something different now?

If Special Relativity is falsified at low speeds, then Special Relativity is falsified.

Granted, but I don't see why you felt the need to say this.

And you're basically saying SR is falsified because an opponent of SR says it's falsified, when it's not.

No, not true. I say that it's falsified because Sagnac's experiment falsified it. Sagnac presents "Proof for the Existence of a Luminiferous Ether", and Einstein calls the luminiferous ether superfluous in his 1905 paper, and presents a theory which contradicts the existence of the luminiferous ether.

On the other hand your strange and incomprehensible reasoning is, that Einstein's Special Relativity could not be falsified by Sagnac as long as Struthio did not show how to explain the "discrepancy in the precession of the orbit of the planet Mercury".

I haven't forgotten the train example at all. And you've agreed already that the train example doesn't refute SR.

Yes, the train example is consistent with Special Relativity and does not refute Special Relativity. It's the Sagnac experiment which falsifies Special Relativity. And your recommendation to compare the train example with the Sagnac interferometer illustrates the falsification:

In the train example, the bolts arrive at Susan's place simultaneously and at Mary's place one after the other. In the Sagnac experiment, the detector shows that the beams arrive one after the other for every observer.

Sagnac is not a recent experiment. If it were recent, I could understand some debate over interpretation. But SR explained it over a century ago. There were SR explanations of the effect even before Sagnac's experiment. It's not as if nobody ever thought about it before.

The fact that you can't understand history is just a declaration concerning you're own ability to deal with reality. You can't use it in place of an explanation how Sagnac's result could be consistent with Einstein's idea that the speed of light is constant in all reference frames.

Sagnac simply disproves Einstein's postulate, and your comment is: That's impossible because then my understanding of how the science establishment works is wrong.

The pulses go in different directions the same distance. Observer M receives these pulses at different times. Does that really sound synchronized from M's perspective?

The question is nonsense. M knows that both beams are split from one of the same beam at the light source. He can reduce the radius of the loop to decrease the fringe shift, which, in the limit, shrinks to zero.

Just had a post Christmas day read of this thread. A 5 month delay with a reply has to be a record. Just to bring us all up to date with this most interesting debate, can I ask is it now about Einstein's Special Theory of Relativity? Is someone saying it has been falsified and the other saying it has not?
Thanks lads.