When you travel at speeds approaching the speed of light, time slows down for you relative to the outside world. If you could travel faster than the speed of light, the time dilation would technically allow you to reach your destination before you even have left, effectively traveling back in time. Unfortunately, the speed of light is the ultimate stop sign in the universe. By the rules of Einstein's Special Relativity, it takes an infinite amount of energy to accelerate a slower-than-light object to the speed of light—the faster you go, the more massive you become and the more energy it takes to accelerate your further. Traveling faster than light would require technology we don't have yet, and that is likely impossible.

Relativity does technically allow for faster-than-light particles called tachyons, but there is no evidence that tachyons exist, or that they could be used to transmit meaningful information (like you) if they did.;
, Wormholes are theoretical warps in the fabric of reality that connect two points of space-time by a shorter distance than they are separated by in the larger continuum. Wormholes could connect distant galaxies, separate universes, and even different times. Much like traveling faster than light, however, the practicalities of stable wormhole creation and travel likely make this option impossible.


Ideas in quantum physics suggest that our universe is full of wormholes—tiny ones smaller than atoms that form and collapse in the briefest instants at the level of reality's quantum foam. Harnessing and expanding one to a size humans could move through, however, might cause a feedback loop that collapses the wormhole before you could use it for time travel.
 If you really have to go back in time but haven't found a way to overcome the practical problems of faster-than-light travel or wormhole creation, you could travel forward in time to a far future out of reach of your natural lifetime. Perhaps in the future, people will have developed advanced technologies that make backward time travel possible, and you can convince them to send you back to your historical destination. Under the laws of physics, travel into the future is much more achievable than travel into the past.


Take a trip at speeds near the speed of light. Special relativity predicts that if you travel at near light speed, time will slow down for you relative to slower frames of reference. So if you spend a few years zooming away from the Earth and back, you will return to find that more years have passed on Earth than have passed for you.
Freeze yourself in suspended animation. Though the technology has hardly been perfected, it may be possible to freeze a human body and thaw it many years later unchanged and un-aged. If you could make yourself such a time capsule, you could last beyond your lifetime and awaken in an age far into the future.
Go faster than light.
Dive through a wormhole.
Travel forward and let the future figure it out.
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