We know that time travel is possible, at least in the forward direction. In this recently released TEDEd video, educator Colin Stuart imagines where and when it might take us, while exploring the science behind time travel and time dilation.
Stuart teamed up with director Franz Palomares and animation artist Godfrey Hibbert to provide this wonderfully lucid explanation of Einstein's general theory of relativity (one of my favorite theories, on account of its surprising conceptual simplicity), time dilation and time travel.
One thing the video doesn't touch on is another form of time dilation known as gravitational time dilation. Also postulated by Einstein, gravitational time dilation shows that objects placed near objects with very strong gravity experience time slower than those further away.