Does time travel exist? I guess the most pertanant answer is that none of us really know. Although we speculate, we cannot be for sure. As for whos grandfather invented the paradox, it really dosen't matter. Sometimes when we don't know the answer to a future question we resort to going back to the past where we find a more comfortable train of thought. Now, my theroy is: To travel through time in a singular dimention seems not to be very likly. First we must realize that there is really no physical time, only what we percieve as a really nice way to chart our memories. I believe that many people are under the impression that once you hit the speed of light everything around you dissappears and you move to a place already prefaceted in the future, this really can't be true though. Like I said earlier, time is a perception, and with this in mind I would believe that no matter what happens after you hit the speed of light(which I wouldn't know what would happen) your perception of time would be the same. Also if you will remember from basic science class its not what rotates around what that determines the perception of time passage, but how fast what you are on is rotating that does, so most likely other persons perception of time passage wouldn't change if you somehow created a craft to transport you at light speed. This is just my opinion and it is subject to criticism. I don't believe myself to be "right", but this is the only way my mind can grasp time travel. Thank you for your time. P.S.- Wormholes are a different story though.