That's Einstein's equivalence principle: "The outcome of any local non-gravitational experiment in a freely falling laboratory is independent of the velocity o

That's Einstein's equivalence principle: "The outcome of any local non-gravitational experiment in a freely falling laboratory is independent of the velocity of the laboratory and its location in spacetime." http://en.wikipedia.org/wiki/Equivalence_principle http://en.wikipedia.org/wiki/Equivalence_principle