Everyone knows that paradox. In true we can say who person is standing,so If we say that the person in earth is standing,then the clock of astronaut will run slower. Else,if we say that astronaut is standing and that earth is moving,we see the clock of earth's person to run slower. So in true when astronaut come back to earth,he will not bigger from other but they will have the same age. Then what other strange happened?? I heard about a gravitational force,when speed of astronaut change. Can you explain more?