I know that there are several experiments (conducted after Einstein's formulation of Special Relativity) that confirm to some extend Einstein's postulate that nothing can travel faster than light. But my question is what motivated Einstein to make this assumption on the first place back in 1905.
A possible answer is due to the wave-like nature of light and the fact that a moving wave-source does not change the speed of the wave as long as the frequency is constant. But is this enough?
Apparently, within the theory, if this postulate is violated, several paradoxes appear. But my question is what motivated the postulate at the first place in order to build the theory based on the assumption that the speed of light is constant in all frames of reference.
I would really appreciate any light on that, as well as any resources or quotes from Einstein himself.