Einstein's postulates of special relativity 1 The same laws of electrodynamics and optics will be valid for all frames of reference for which the equations of mechanics hold good 2 light is always propagated in empty space with definite velocity c,which is independent of the reference system that we choose.1 The same laws of electrodynamics and optics will be valid for all frames of reference for which the equations of mechanics hold good 2 light is always propagated in empty space with definite velocity c, which is independent of the reference system that we choose. Einstein’s postulates of special relativity