Since time travel is being brought up I want to clarify how it works.
As some have mentioned time travel to the past is not possible. Time travels only in one direction and that direction is forward. Time travel to the future though is definitely possible. However, it works a bit differently than what you might normally expect. The concept was explained well by Einstein in his Special Theory of Relativity. Here he established the concept of time dilation. Time dilation is best explained with frames of reference. Imagine someone in a spaceship and someone observing the spaceship from the Earth. If the person inside the spaceship travels close to the speed of light (say 80% of it) to a nearby star and the trip takes them 5 years from Earth's frame of reference 8.33 years would have passed. So that means if we had both people, the one on Earth and the one on the ship be 30 years old, once the person on the ship returns they would be 35 while the one on Earth would be 38 or so. Or in other words, 8 years have passed on Earth by the time the person on the spaceship returns when compared to the 5 that did for the traveler. This difference of course is further increased the closer you travel to the speed of light. It is important to note that anything other than massless particles cannot travel at the speed of light.
For those curious the mathematical formula itself is:
t' = (t / sqrt(1-(v^2/c^2)))
t' would be the person on Earth's time
t would be the person on the ship's time
v would be velocity
c is the speed of light = 3.0 * 10^8 meters/second