Ther was an experiment where scientists built two ultra precise clocks. One of them stayed on earth while the other was sent to space orbiting the earth at much higher speed than the one left behind. Once the clock from space was returned scientist observed that time on the clock in space progressed slower relative to the on the one from earth.

Which proves Einstein's predictions based on General Theory Of Relativity.

This is being considered when e.g. sending probes to Mars.