(I heard this in a movie and I think it’s pretty cool.)
A man is born in 1955. Today, the 14th of August, 2017, he is 18. How is this possible?
At the risk of giving the obvious answer(s),
or, almost equivalently,
- He’s been in suspended animation / stasis for 44 years.
- He’s been travelling in space for $n+44$ years at such (relativistic) high speed that only $n$ years have passed for him during his trip, so he’s aged only $n$ years. (And he’s spent only $18-n$ years on Earth.)