With respect to time dilation, apparently Russian Cosmonaut Sergei Avdeyev, who spent 747 days (64 540 800 seconds) aboard the Space Station Mir which travels at 7600 ms-1 experienced 21 milliseconds less than colleagues on Earth. If Sergei Avdeyev considered himself stationary and the Earth travelling at 7600 ms-1 would he not have experienced 21 milliseconds more than colleagues on Earth?
How does this work? In a more idealised twin example it may be quite arbitrary as to which party is stationary so when they reunite who is older or younger?
