<Li> Experiments to test emission theory demonstrated that the speed of light is independent of the speed of the emitter . </Li> <Li> Experiments to test the aether drag hypothesis--no "aether flow obstruction". </Li> <P> Special relativity uses a' flat' 4 - dimensional Minkowski space--an example of a spacetime . Minkowski spacetime appears to be very similar to the standard 3 - dimensional Euclidean space, but there is a crucial difference with respect to time . </P> <P> In 3D space, the differential of distance (line element) ds is defined by </P>

Who are some to which two theories do lines 1-2 refer