Einstein's Train Thought Experiment

[Doc Al]

Let me put this way,
1. Observer moving with velocity v and source of signal from the front and rear are stationary from stationary reference. Observer is stationary with his own reference and source of signal is moving at velocity -v. These two are identical. This doesn't talks about speed of signal so invariance of c is not required.

Why do you think the speed of the source is relevant?

Make it simple. Set it up like this: There are giant flash bulbs at each end of the train. Now the source of each flash moves with the train, so the speed of the source is zero with respect to the train observer.

The setup is the same: The bulbs flash at the same time according to the track observer.

Now what?

 

[Nugatory]

2. Simultaneity of the observer in the train breaks because of c+v and c-v in his frame. Here v is the prime variable for break down of simultaneity and not c. If v goes to zero observer will receive the signals simultaneously. Here also c is irrelevant, only condition is c in c+v and c in c-v must be same. Since c+v and c-v is on the same frame. Frame invariant condition is not required for this.
...
Can someone explain which one of these three points are wrong in classical sense. And why frame invariance of speed of light affects required.

#2 is predicted by Newtonian mechanics, but is demonstrably false (google for "Michelson-Morley experiment") and also is not predicted (but not precluded) by the laws of electricity and magnetism (google for "Maxwell's equations", look at the derivation of $c$ there).

You are right about what happens when $v$ goes to zero... But that's going to be true of all theories.

 

[duri]

#2 is predicted by Newtonian mechanics, but is demonstrably false (google for "Michelson-Morley experiment")

If I interpret Michelson-Morley experiment in other way. There is no relative motion between source and observer in observer's frame. So, I can't expect changes in fringe pattern what ever angle the table is rotated. Assumption of ether flowing with velocity v is what demonstrated as incorrect.

Take for example ripple in the water. It doesn't matter observer moves or water container moves, as long as water doesn't flows waves would reflect back at same time. Only in case of water flows, wave reflects at different time. Its all about relation between medium and energy moving through the medium. In case of light since there is no medium, relative velocity is not possible to define between wave and medium. Light has to travel at same speed in vacuum. This also given by electromagnetic properties of vacuum.

I got some understanding while replying this. But I got new confusion too, If medium velocity is the key factor (which is not the case for light in vacuum). How inertial frame comes into picture.