The laws by which the states of physical systems undergo change are not affected, whether these changes of state be referred to the one or the other of two systems of coordinates in uniform translatory motion.
2. Second postulate (invariance of c)
As measured in any inertial frame of reference, light is always propagated in empty space with a definite velocity c that is independent of the state of motion of the emitting body.
Alternate Derivations of Special Relativity
The two-postulate basis for special relativity outlined above is the one historically used by Einstein, and it remains the starting point today. However Hendrik Lorentz and Henri Poincaré derived their version of the theory from Maxwell's equations and the principle of relativity. The Minkowski space formulation is also used. As Einstein himself later acknowledged, the derivation tacitly makes use of some additional assumptions, including spatial homogeneity, isotropy, and memorylessness. in 1910 and many others in subsequent years) that special relativity follows from just the relativity... Read More