Experiment 7: Mrs. Einstein is standing in a field and she sees two simultaneous flashes of lightning. Mr. Einstein is on a railroad car moving to the left with velocity v.

Question: What will Mr. Einstein see?

Answer: Mr. Einstein will see the light flash on the left first since he is moving toward that light and away from the flash on the right. Thus, he will not agree that the flashes of light occurred at the same time. In fact, from his perspective, Mrs. Einstein is the one that is moving, and he will say that it is only because of her movement that she happened to perceive both flashes of light as happening simultaneously.