Of all the riddles of the universe, time travel may be the most perplexing. When you travel through time, strange things start to happen. Imagine visiting yourself in the past? You could jump into the future, while aging very little. Some humans have already made the trip. See how it's all possible as this video explores and unravels the mystery of time travel.
But if Time Travel ever does exist, surely it must exist now? To have a device that does so, you can travel back to the dawn of time or to the birth of the Earth, which means it will have always existed... paradox.