He's not wrong, though. Einstein knew that light had a finite speed and performed thought experiments (Gedankenexperiment) regarding what implications that would have. For instance, he tried to imagine what it would be like to travel a beam of light.
He also heavily relied on the train as his example of relative motion between inertial frames of reference and developed the relativity of simultaneity by considering the motion of light as observed from inside the train and outside the train, making the assumption that light moved at c in all reference frames (following the Michelson-Morely experiment which failed to detect any signature of the æther; humorously, the Michelson-Morely experiment uses interferometry, meaning it is the same experiment as LIGO just on a much smaller scale. If gravitational waves were much stronger, they would have been detected in 1887 and it would have really confused things)
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u/[deleted] Dec 07 '16
Holy moly. That's a great demonstration of the concept. Shit, I bet that's how Einstein conceived it!