According to Oxford philosopher Nick Bostrom, the chances are pretty good that we're currently existing not in the "real world," but instead are a vast computer simulation created by a future, further advanced version of ourselves. Yeah, crazy, I know. Basically, he argues that because computing power will advance to the point where a system could be built that could simulate every brain on earth, future "posthumans" could set up an "ancestor simulator" that would be indistinguishable from real life for the inhabitants.
I'm totally not stoned enough for this to really blow my mind, but it's a really interesting theory. While Bostrom thinks there's a 20% chance of our entire world being a computer simulation, John Tierney of the New York Times thinks the odds are closer to even. But hey, even if it's true and this is really all happening in some future nerd's PC, it's not so bad, is it? As long as the computer doesn't overheat; that'd be a really lame way to go. [NY Times]