Captain Ray, on the Galactic Explorer, sets off bright signal lights at the two ends of his spaceship so that they are seen as flashing simultaneously by General Kay, who is watch the ship go by. General Kay concludes that she was next to the midpoint of the ship at the instant when the lights flashed in her reference frame. This can only happen if Captain Ray, at the center of the Galactic Explorer,
A) sees the lights flash simultaneously in his coordinate system.
B) sees the bow (front) light flash before the aft (rear) light.
C) sees the aft (rear) light flash before the bow(front light.
D) can calculate that the light flashes reach General Kay so that the flash from the bow light reaches her before the flash from the aft light.
E) can calculate that the light flashes reach General Kay so that the flash from the aft light reaches her before the flash from the bow light.

Question

Quizplus · Accepted Answer

According to the theory of relativity, if two events (such as the flashing of lights) are simultaneous in one frame of reference (General Kay's), they are not necessarily simultaneous in another frame of reference that is moving relative to the first (Captain Ray's on the Galactic Explorer). Since General Kay sees the lights flash simultaneously while she is at the midpoint of the ship, it means that in Captain Ray's moving frame, the light from the bow (front) must have been emitted earlier than the light from the aft (rear) to account for the time it takes light to travel to the midpoint from each end of the ship, given the ship's motion relative to General Kay.

Captain Ray, on the Galactic Explorer, Sets Off Bright Signal