Quoting from Wikipedia: "Time dilation would make it possible for passengers in a fast-moving vehicle to travel further into the future while aging very little, in that their great speed slows down the rate of passage of on-board time. That is, the ship's clock (and according to relativity, any human travelling with it) shows less elapsed time than the clocks of observers on Earth. For sufficiently high speeds the effect is dramatic. For example, one year of travel might correspond to ten years at home. Indeed, a constant 1 g acceleration would permit humans to travel through the entire known Universe in one human lifetime. The space travellers could return to Earth billions of years in the future. A scenario based on this idea was presented in the novel Planet of the Apes by Pierre Boulle." From my understanding of time dilation, this is an incorrect interpretation of its effects. Observer A's clock on earth would experience a slowing of the clock on Spaceship B (traveling close to speed of light) as it moves away from A. However, should B turn around and come back towards A with same speed, A would then experience that B's clock is speeding up the same amount. Hence, when spaceship lands, A and B clocks would show the same time. This would make the notion of time travel into the future by boarding a fast spaceship that travels with speeds close to speed of light an impossibility. Time dilation is not about actual slowing of the passing of time on an object traveling close to speed of light, but the about the slowing of THE EXPERIENCE of that time that a relatively stationary object has. If that is the case, then roundtrips must cancel out this effect, making travel into the future a logical impossibility no matter what kind of propulsion we can invent for spaceships.