7.5+ Boxcar with a bomb. A railroad boxcar has a clock mounted on its front wall and a clock mounted on its rear wall, and a package at its very center. Each clock is attached to a flashlight aimed at the package, and each flashlight is programmed to flash momentarily when its clock strikes noon. Within the package is a bomb set to explode if it gets a light signal from one flashlight or from the other, but not if it gets a signal from both. The boxcar travels down a track at high speed. Susan analyzes this situation from the boxcar's frame: "The two flashlights flash simul- taneously, the two light signals travel the same distance, and the two light signals reach the package simultaneously. Therefore, the bomb does not explode." Roth analyzes this situation from the Earth's frame: "The two flashlights flash simulta- neously, but the bomb is moving away from the rear (left-hand) light signal and toward the front (right-hand) light signal. The front light signal thus has less distance to travel, so it arrives at the package first. Therefore the bomb does explode."

7.5+ Boxcar with a bomb. A railroad boxcar has a clock mounted on its front wall and a clock mounted on its rear wall, and a package at its very center. Each clock is attached to a flashlight aimed at the package, and each flashlight is programmed to flash momentarily when its clock strikes noon. Within the package is a bomb set to explode if it gets a light signal from one flashlight or from the other, but not if it gets a signal from both. The boxcar travels down a track at high speed. Susan analyzes this situation from the boxcar's frame: "The two flashlights flash simul- taneously, the two light signals travel the same distance, and the two light signals reach the package simultaneously. Therefore, the bomb does not explode." Roth analyzes this situation from the Earth's frame: "The two flashlights flash simulta- neously, but the bomb is moving away from the rear (left-hand) light signal and toward the front (right-hand) light signal. The front light signal thus has less distance to travel, so it arrives at the package first. Therefore the bomb does explode."