[Ghoulish Delight]

There's no supposedly about it. Time dilation (the slowing down of time for an object traveling at speed relative to an object at rest) is a central, and experimentally confirmed, component of Einstein's theory of relativity. It's what gives rise to the famed twim paradox.

It does pose some interesting issues. For example, let's assume that we satisfy ourselves with near-light speed travel. An astronaut could conceivably at those speeds reach another solar system 10 lightyears away (there are several that distance and closer). The good news: At those speeds, from the frame of reference of said astronaut, the distance will actually shrink (which is another way of expressing time dialation, I'm really still talking about the same effect), so it should take less than 10 years. The bad news...if it takes 8 years from the astronaut's perspective (16 total for the round trip), when he comes back, it will have been the full 20 years (okay, slightly longer if he's just under the speed of light).

As the distance increases, so does the gap. So there's a built in advantage and a built in disadvantage. The advantage is that the distances would be slightly more reachable than they'd appear from our perspective, allowing an astronaut to cross them in a fraction of the time that the measured distance might indicate. The disadvantage is that by the time the astronaut gets back, time on earth will have passed him by. He may have aged a couple years, while full generations have gone by at home.