It’s likely that we can’t do time travel. But we don’t know for sure. The arrow of time comes from the increase of entropy, meaning that the universe started out organized and gets messier as time goes on. Every way in which the past is different from the future can ultimately be traced to entropy.
NYT: Sean Carroll Talks Time Travel
NYT: Sean Carroll Talks Time Travel
http://www.nytimes.com/2010/04/20/scien ... ef=science