SR is based on the postulate that all physics experiments yield the same results regardless of inertial reference frame? What was Einstein's basis for this assumption? What thought process did he go through to come to that conclusion? How could he know the speed of light was the same regardless of inertial reference frame when he did not have the experimental apparatus at the time to know? People have said that the measurement of e0 and mu0 are the same in all reference frames, so therefore the speed of light must be the same in all reference frames. I am not entirely convinced by this statement.