Question: How does the theory of relativity?

Jim Barrett answered on 11 Mar 2016:

The theory of relativity says a bunch of different stuff, but it all comes down to two facts; You can’t travel faster than light and you wouldn’t be able to tell the difference between standing on earth or being in an elevator in space.

From these two facts alone we can work out that people age slower when they move really quickly, and we can understand how gravity works even in crazy situations (like when 2 black holes collide)