Originally posted by elfmotat
Into the future: Yes, special relativity allows it. If you travel near the speed of light, time slows down for you while it continues at its regular rate for everyone else.
Into the past: No. The only way I can think of would be a wormhole, and those would require about the energy of an entire star to produce. They would also produce paradoxes like the grandfather paradox, and feedback would cause them to be destroyed before they could be put to any use.
Now for us to wait for the noobs who have no idea what they're on about...