Time Travel Isn’t Possible … or Is It?

Special relativity teaches us that the three dimensions of space and the solitary dimension of time are woven together like a fabric. It's impossible to think of them as separate entities, only a singular unified entity — space-time. We can't think of motion through space without being mindful of motion through time, and vice versa. Left-right, up-down, back-forth and past-future are all on equal footing.

And yet, time does seem a little different. We have complete freedom of movement within space, but we cannot avoid our future. Time seems to have an "arrow," whereas the spatial dimensions are ambidextrous. Given the unity between time and space, it leads to the obvious question: Is time travel, of any sort, possible? Under any circumstances? At all? [How Time Travel Works in Science Fiction (Infographic)]
Into the future: Sure

Oddly enough, the answer is yes! We cannot avoid moving into our futures, but we can control the rate that we move through time. This is a consequence of another lesson from relativity: Not all clocks are the same.

The speed at which you move through space determines the speed at which you move through time. In the succinct phrase: Moving clocks run slow.