This is Sergei Vasilyevich Avdeyev. He is a time traveller.
Albert Einstein’s special theory of relativity states that the faster you travel, the slower time runs.
Sergei Avdeyev spent 748 days on the Mir space station travelling at an average speed of 17,000mph so for him time is about 20 milliseconds behind everyone else on Earth.
Put another way, Sergei Avdeyev is 20 milliseconds younger than he would have been if he had never travelled in space.
Are you sure he’s 20 milliseconds younger. Wikipedia says that he’s 20 millisecounds older, (supported by Gott, J. Richard (2002). “Time Travel in Einstein’s Universe”. p. 75).
You have considered special relativity but what about general relativity. “clocks at lower potentials in a gravitational field — such as in close proximity to a planet — are found to be running slower.”(wikipedia)
Time travels slower the faster you go. Therefore if you travel quicker than everyone else you are younger than everyone else.
“…if you travel quicker than everyone else you are younger than everyone else.”
Not quite. Sam is correct about there being some effects from both special and general relativity being at play but he was wrong about wikipedia (or it’s been corrected) in that the difference from the speed is GREATER than the difference due to gravity and thus they do age slower.
However, someone at sea level ages slower than someone on top of Everest, even though the mountain climber is moving FASTER, because in this case the effect from the difference in gravity is greater than the difference from speed (the speed of the ISS is over 40,000mph, or almost double that of someone on the equator, and the gravitational difference is on the order of 6% less, where-as the difference in both gravity AND speed is around 0.1% for the mountain climber.)