The mirror M 2 is partially silvered allowing a fraction of the laser light to escape. Laser arrangement for testing the isotropy of the speed of light. The beams from two lasers, A and B , are combined by the partially silvered mirror P and observed at the detector. Lightning strikes the ground at both ends of a moving train. According to a ground based observer, O g , the strikes are simultaneous.
Lightning strikes the ground at both ends of a moving train.
According to a ground based observer, O g , the strikes are simultaneous. L moving to the right. Worldlines of front and back are shown as light solid lines. In the train frame it reaches the ends simultaneously. A light flash expands as a sphere in every direction and lengths, d , transverse to the direction of motion are unaffected by the relativity of simultaneity.