An interesting (IMO) theory related to Albert Einstein's famous Theory of Relativity. Einstein discovered that light is observed moving at the same speed no matter what speed the observer is moving. This led to an interesting paradox; If you are 'standing still' and measure the speed of a light ray coming at you, you will measure it at about 300,000 kilometers a second. However, if you are travelling at 1/2 the speed of light and measure a ray of light coming at you, you will still measure it's speed at 300,000 K/sec. Through these realizations, Einstein discovered that the closer you get to the speed of light, the slower percieved time moves. This was later proved correct when 2 cesium clocks were syncronized on Earth and then one was taken on a space shuttle mission. At the end of the mission after the shuttle landed, the times were compared and the clock that was in space travelling at 20,000 miles an hour was slightly behind the clock that remained on Earth.

I wonder what it would be like to actually travel at close to (remember E=MC^2 so you could never travel at light speed) the speed of light... that would be trippy. You would have travelled YEARS in earth time, your great-great grandchildren would be dead, but you have only been travelling a couple of minutes...