Starts With A Bang #19: Is Time Travel Possible?

Is time travel possible? Of course it's inevitable in some sense, as we always move through the Universe at the "boring" rate of one second per second. But what about traveling into the future? If we go, can we ever come back? And what about back in time? Would it be possible to alter the past, or revisit a historical event as an observer? The mathematics of relativity opens the door to a lot of possibilities, but the physical Universe has a lot to say about it, too.