<Li> The laws of physics are the same for all observers in uniform motion relative to one another (principle of relativity). </Li> <Li> The speed of light in a vacuum is the same for all observers, regardless of their relative motion or of the motion of the light source . </Li> <P> The resultant theory copes with experiment better than classical mechanics . For instance, postulate 2 explains the results of the Michelson--Morley experiment . Moreover, the theory has many surprising and counterintuitive consequences . Some of these are: </P> <Ul> <Li> Relativity of simultaneity: Two events, simultaneous for one observer, may not be simultaneous for another observer if the observers are in relative motion . </Li> <Li> Time dilation: Moving clocks are measured to tick more slowly than an observer's "stationary" clock . </Li> <Li> Length contraction: Objects are measured to be shortened in the direction that they are moving with respect to the observer . </Li> <Li> Maximum speed is finite: No physical object, message or field line can travel faster than the speed of light in a vacuum . </Li> <Li> The effect of Gravity can only travel through space at the speed of light, not faster or instantaneously . </Li> <Li> Mass--energy equivalence: E = mc, energy and mass are equivalent and transmutable . </Li> <Li> Relativistic mass, idea used by some researchers . </Li> </Ul>

Who proposed the concept of all motion is relative