Does the train embankment thought experiment of Einstein really demonstrate relativity of simultaneity?

Question

The title of the question have been changed as the second part of the question might have referred to a duplicate question. Yet the edits are rejected with no additional reason! The closure of this question hence seems to me to be a political decision to enforce censorship and restrict free discussion. Is this good for science?

Einstein concludes that “according to Einstein [16, p25-26] “the observer will see the beam of light emitted from B earlier than he will see that emitted from A .” He concludes “Observers who take the railway train as their reference-body must therefore come to the conclusion that the lightning flash B took place earlier than the lightning flash A .”

In 1 the viewpoint of Einstein is questioned:

“This demonstration suffers from a serious flaw. Since the train is moving at constant speed, it constitutes an inertial frame and therefore according to the light speed invariance postulate, light speed within the train is constant in all directions. Therefore the two light beams that move toward observer O’ travel at the same speed within the frame of the train and since they travel the same distance will meet at observer O’ in the train just as they did with the observer O on the embankment. It follows that the observer on the train, according to the theory, perceives the lightning strikes to be simultaneous just as the observer on the embankment. This contradicts relative simultaneity described above in the thought experiment by Einstein and used by almost every textbook writer on the subject to demonstrate the phenomenon.”

In [2] an Absolute Lorentz transformation (ALT) is proposed that

“has similar kinematics to special relativity yet maintains absolute simultaneity in the context of a preferred reference frame.“

In [3] the concept of RoS is shown to be in conflict with the principle of relativity.

1. https://www.researchgate.net/project/Relative-Simultaneity-Does-Not-Exist

2. https://journals.plos.org › article › jo...Implications of an Absolute Simultaneity Theory for Cosmology ...

3. https://vixra.org/abs/1805.0273

Answer 1

“[...] Therefore the two light beams that move toward observer O’ travel at the same speed within the frame of the train

Yes.

and since they travel the same distance will meet at observer O’ in the train just as they did with the observer O on the embankment.

They would if they were emitted at the same time, but they weren't emitted at the same time. That's the whole point. Einstein's argument is:

• With respect to the ground frame, you can show that the beams reach O' at different times.

• Therefore, with respect to the train frame, the beams reach O' at different times, because it's the same person and the same experience.

• If they were emitted at the same time in the train frame, they would reach O' at the same time, which is a contradiction. Therefore, they were emitted at different times in the train frame.

This guy is almost making Einstein's argument, except that he assumes there is no relativity of simultaneity when he assumes that the beams were emitted at the same time in the train frame. Of course if you assume that then you get a contradiction, because there is relativity of simultaneity.

Answer 2

The relative nature simultaneity follows inescapably from the assumption that the speed of light is the same in all interval reference frame, and that has been confirmed in countless experiments.

There are many papers on the Internet that purport to refute SR. Life is too short to read all of them, but all of those I have had the time to study properly have had a common denominator, which is that their author misunderstands the very theory they aim to refute.

In the case of the first paper you cite, the author supposes that two light flashes meet at the observer O and and the observer O' who is somewhere else at the time, in other words that the same event happens in two different places at once. Indeed, if we extend the thought experiment to have n different trains moving at different speeds on parallel tracks, the logic of the author requires that the same event occurs at n different places. Also, as @benrg points out, the author implicitly assumes from the outset that the emissions of the two beams were simultaneous on both the train and the platform, which is directly incompatible with the theory he thinks he is illustrating.

In the third paper you cite, the author utterly misunderstands the point of Einstein's thought experiment. He goes on to mention a second observer on the train at M'' who is not at the centre of the carriage but towards the rear, and who is passing directly alongside the observer on the platform when that person sees the two rays of light meet. Thus, the author argues, the emission of the light could appear to have been simultaneous to the observer at M'' on the train- there he fails to notice that that would require the speed of light to be anisotropic on the train and to be anisotropic in the opposite direction in a second train observing the experiment when heading in the other direction.

The second paper you cite is a much more learned piece of work, far too long for me to assess properly, but I did note that it mentions that the 'Alternative Lorenz Transform' theory which the author explores assumes there is a preferred reference frame, and the author points out that coincidentally the experimental evidence suggests that the Earth is the preferred reference frame! In fairness the author goes on to speculate that there might be other local preferred reference frames each being centred on a massive body such as the Earth. Fine. I will suspend judgement until someone finds experimental evidence to the support the supposition.