Time travel to the future in physics
Twin paradox diagramThere are various ways in which a person could "travel into the future" in a limited sense: the person could set things up so that in a small amount of their own subjective time, a large amount of subjective time has passed for other people on Earth. For example, an observer might take a trip away from the Earth and back at relativistic velocities, with the trip only lasting a few years according to the observer's own clocks, and return to find that thousands of years had passed on Earth. It should be noted, though, that according to relativity there is no objective answer to the question of how much time "really" passed during the trip; it would be equally valid to say that the trip had lasted only a few years or that the trip had lasted thousands of years, depending on your choice of reference frame.
This form of "travel into the future" is theoretically allowed using the following methods:[6]
Using time dilation under the Theory of Special Relativity, for instance:
Traveling at almost the speed of light to a distant star, then slowing down, turning around, and traveling at almost the speed of light back to Earth[21] (see the Twin paradox);
Orbiting Earth for long periods of time (practical, but insignificant);
Using time dilation under the Theory of General Relativity, for instance:
Residing inside of a hollow, high-mass object;
Residing just outside of the event horizon of a black hole
Additionally, it might be possible to see the distant future of the Earth using methods which do not involve relativity at all, although it is even more debatable whether these should be deemed a form of "time travel":
Hibernation
Suspended animation
