Learn and Understand the Theory of Relativity

Surely, you have heard the story of the astronaut coming back
to earth, looking as young and fit as when he left, with
everybody else on earth hardly being able to walk because of
the years added to their age, as a result of the difference in
how time passed on Earth as opposed to the time passing
over the astronaut. Many would argue that this is just an
illusion, when in fact, although not literally true, there is a
scientific explanation for this: indeed, you must have guessed it
by now, Einstein...