Moving objects appear shorter than when at rest!
All observers agree:
- Each of the two conductors at the ends of the train each sees a pole next to his end of the train at the moment he sees a flash
But they do not agree that this was at the same time.
- Since we define the length by measurement of positions at the same time, the length must change for different observers
- To a person on the ground:
- Everything about the train appears to contracted in the direction of motion - the people on board, the atoms, . . .
- The “gedanken experiment” can also be reversed!
- The a person on the train, everything on the ground appears contracted to them!