Special Theory of Relativity

Galilean transformations imply that all physical laws remain identical in uniform motion. If the Galilean transformations are inserted into Maxwell's equations, they do not remain identical [Problem:1]. Moreover, Maxwell's theory concludes that a disturbance in the electromagnetic field travels at the same speed (speed of light) in all directions even if the source of the disturbance is moving. Michelson-Morley's (M-M) experiment shows that velocity addition theorem does not work for light [Problem:2]. In order to solve the two problems, Lorentz devised a set of transformations. Under Lorentz transformations Maxwell's equations remain identical, and the length contraction (required by the transformation) account for the null result in the M-M experiment. Einstein said, all physical laws are identical under: not Galilean, but Lorentz transformations. And that's it.