An Observer Sees Two Spaceships, S₁ and S₂, Each Having

Essay

An observer sees two spaceships, S₁ and S₂, each having the same length in its own rest frame, traveling toward each other along parallel lines from opposite directions, with equal speeds relative to the observer. As seen by this observer, the two spaceships have the same length and, when they are next to each other, the nose of one coincides with the tail of the other, and vice-versa. However, as seen by passengers on either one of the spaceships, the other spaceship is shorter than their own, so if the tail of the other spaceship is in line with the nose of their spaceship, the nose of the other spaceship cannot be lined up with the tail of theirs. How can you explain this discrepancy?