Ford: Is time travel even possible?
McKay: Well, according to Einstein's general theory of relativity, there's nothing in the laws of physics to prevent it. Extremely difficult to achieve, mind you. You need the technology to manipulate black holes to create wormholes not only though points in space, but time.
Sheppard: Not to mention a really nice DeLorean.
McKay: Don't even get me started on that movie!
Sheppard: I liked that movie!