Einstein's relativity tells us that time travel is possible, but you can only go *back* in time by traveling near the speed of light relative to the earth. Essentially if you were to travel really fast and really far in a space ship and then return to Earth, you would have traveled back in time.
thats incorrect. According to Einstein's theory, If you travel really fast and far time would slow down for the spaceship and its contents. Time on earth would continue as it always does. So for the space ship (relative to the spaceship), earth's time woulds time appear to be running faster than its own. Imagine earth's time in fast forward. So once the space ship returns, Earth and all its contents would have aged more than the space ship and its contents. As an example lets say 100 yrs earth time passed but for the space ship they experienced only one year (these numbers were chosen for simplicity but there one could even calculate projected time deviations). So if you think about it, your not going back in time.
Some people conceive this as "time travel" into the future. they picture a person getting in a ship and driving hundreds or thousands of years into the future. In reality, its really not science fiction. Its the way the universe works. I could talk all day about my thoughts on such but i dont have the time. I hope i explained this well, its just the tip of a great big ole iceberg.