You want a headache? Try to understand this.
The theory of relativity says that as you approach the speed of light, time slows down. Note: You cannot reach the speed of light. (c=speed of light=299,792.458 km/s)
Ok, so say you wanted to take a trip from Earth, to the star Vega. This distance is 25 light years. Pretty big distance right? Wrong. Believe it or not, it would not take 25 years to get there if you are traveling close to the speed of light. This is because time slows down as you approach the speed of light.
If your were traveling at a velocity of .999c (99.9% of the speed of light), the distance between the Earth and Vega would actually contract to about 1 light year. The time it takes to travel this distance at that speed would be about 2 years.
What's really interesting about this? While you are traveling that distance, at that speed, what seems like only 2 years to you, would be 50 years to someone on Earth.
As said before, the closer you get to the speed of light, to slower time gets for you.
What does all this mean? It means that theoretically, it is possible to travel to other solar systems within only a few years.
It also means that time travel is actually possible in the forward direction. To make it to Vega and back would only take you 4 years, but the Earth would age 100 years.
Now then, if it were possible to reach 99.9% of the speed of light now, we could send someone to the year 3013, and it would only take them 40 years to get there. That's 1000 years, and it would only take 40 years to get there.
Now I have to go take a test over some of this. (not the time travel, just the theory of relativity)