It’s actually possible to time travel…but only in one direction. Einstein found out that time is not an absolute value but is actually different for everything and everyone. His theory of special relativity states that time passes slower for objects moving quickly, as described by the equation ∆t‘ = ∆t/√(1-ß^2), where ∆t is the time experienced by a stationary object, ∆t‘ is the time experienced by a moving object, and ß is that object’s speed as a fraction of the speed of light.  So the 60 seconds you spent reading this lasted 2.13*10^-13 seconds less for that car driving by at 40 mph.

So in a fast enough spaceship, you could spend 5 years out in space and return to Earth 20 years later.

Skeptical?  This theory has been confirmed by observing the rates of certain chemical processes at high speeds, and GPS would not work without accounting for the relativistic effects of the fast-moving satellites.