Einstein's train-lightning scenario doesn't demonstrate relativity

  • #26
vanhees71
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No. In Einstein's scenario, the two light-strokes happen (in the rest frame of the train) at different times.
I think, it's important to clearly define which of the many train scenarios we are discussing. There are many in the literature!

There are at least three that come to my mind:

(a) two light signals are sent from the front and the rear of the train simultaneously to the observer at restin within the train located in the middle of the compartment.

(b) two light signals are sent from the front and the rear of the train simultaneously to the observer at rest on the platform.

(c) a (spherical) light wave is sent from the observer in the middle of the compartment. Then you can discuss when the signal reaches the front and rear end of the train from the point of view of the observer in the train the one at the platform.
 
  • #28
vanhees71
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Ok, but then it's clear that the observer ##M'## (moving with the train) observes the signal from B before the signal from A, while the signals reach ##M## (at rest on the embarkment) simultaneously. That's also very clearly written by Einstein.
 
  • #29
That's also very clearly written by Einstein.
A little bit problematic for understanding may be, that he used the same letters ##A## and ##B## for events and positions:
Einstein said:
But the events ##A## and ##B## also correspond to positions ##A## and ##B## on the train.
Source:
https://en.wikisource.org/wiki/Rela..._I#Section_9_-_The_Relativity_of_Simultaneity

Proposal for naming: For event ##A##, position in frame ##S## is called ##a## and position in frame ##S'## is called ##a'## ...

Ok, but then it's clear that the observer ##M'## (moving with the train) observes the signal from B before the signal from A, ...
Yes. Einstein concluded correctly from this:
Einstein said:
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##.
 
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  • #30
vanhees71
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Events are independent of the coordinate system. So event A and event B has a frame-independent meaning. Only the their space-time coordinates change under a Lorentz transformation.
 
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