Question

Two babies are born in a moving train, one in the compartment adjacent to the engine and other in the compartment adjacent to the guard. According to the train frame, the babies are born at the same instant of time. Who is elder according to the ground frame?

Answer 1

Here, the train is in a moving frame and the clocks of the moving frame are out of synchronisation.
If L₀ is the rest length separating the clocks and v is the speed of the moving frame, then the clock at the rear end leads the one at the front by L₀v/c².

Thus, the baby adjacent to the guard cell is elder to the baby adjacent to the engine.