Two observers on the train both standing at midpoint M'. One knows he is on a moving train and takes the embankment as his reference frame. The other observer takes the train as his reference frame.
The lightning strike occurs at A on the embankment and A' on the train and the light from the lightning strike reaches the observers on the train simultaneously.
The observer who knows he is on a moving train, and takes the embankment as his reference frame, says the light traveled from A on the embankment to reach them.
The observer who takes the train as his reference frame says the light traveled from A' on the train to reach them.
Both observers agree that there was a single lightning strike and they agree that the lightning strike reached them simultaneously but they disagree on the distance the light traveled to reach them.
The only way all this could occur is if the light from the lightning strike travels at different speeds to reach the two observers.
Edited by mpc755, : Clean up.
™ Version 4.2
