Time travel used to be thought of as just science fiction, but Einstein's general theory of relativity allows for the possibility that we could warp space-time so much that you could go off in a rocket and return before you set out.
“Everything must change and you do what you can with the changes that are made. You can't stop it. You can't fight it. Everybody tries to go back to yesterday, but you can't go back to yesterday. The only time there is, is now.”