The promise of time travel has long been one of the world's favorite scientific "what-ifs?" Hawking explores all the possibilities, warping the very fabric of time and space as he goes. From killing your grandfather to riding a black hole, we learn the pitfalls and the prospects for a technology that could quite literally, change everything. Written by
Did You Know?
Near the end of the episode, when they are traveling on their hypothetical time travel ship, the narrator says they travel farther than possible. After two years they are traveling at 50% the speed of light. After another two years, they pass the nearest neighboring star, Alpha Centauri. Alpha Centauri lies about 4.25 light years distant. It would be impossible to pass it after only 4 years even if they started off at the speed of light. See more