Yeah, that's the sort of thing that can make you a little crazy, if you think about it too much.
It's something that computer scientists like to point out. The basic idea, as I understand it, goes like this:
- A sufficiently sophisticated computer could run a simulation of the Universe.
- There are potentially lots of computers out there running simulated Universes.
- There is only one real Universe.
- Therefore it is more probable that we are living in a computer-simulated Universe than that we're living in the real one.
- Sleepless nights ensue.