Who first studied variable speed of light? --- Einstein Variable speed of light is a hypothesis that states that the speed of light, usually denoted by c, may be a function of space and time. Einstein's first mentioned a variable speed of light in 1907, and he reconsidered the idea more thoroughly in 1911. ( http://en.wikipedia.org/wiki/Variable_speed_of_light ) As we know, Einstein developed his special theory of relativity, in which the constancy of light speed is a fundamental hypothesis. But I don't understand why he tried to set up the theory of variable speed of light. Does it not contradict the special theory of relativity?