Suppose that A', B' and C' are at rest in frame S', which moves with respect to S at a speed v=056*c in the +x direction. Let B' be located exactly midway between A' and C' in S', with A' and C' 10000 km apart; all are on the x-axis. At t'=0, a light flash occurs at B' and expands outward as a spherical wave. What is the magntidue of the difference in the arrival times of the flash wave at A' and C' in frame S' and S. I know for sure that in frame S', the magnitude of the difference is 0. But should it also be the same in frame S since it takes the same amount of time for the light flash to travel to both A and C, which are the same distance apart? Thanks.