Time Travel to the Past will never be possible

"Very clever" Thank you. :) Re: Point 1 "Of course, I meant the ability to physically travel backward in time to a previous date." For now I will merely note that my opponent has conceded the semantics arguments. Rather than belabor the point, however, I will proceed to arguments of substance. Re: Point 2 "My first argument as to why this would never be possible is because it presupposes that the past is in constant existance as a physical thing (as opposed to a memory) which is not logical. When things move into the past they are no longer there physically. This lack of a physical realm makes it impossible for people to physically go there because it no longer exists." My opponent makes a valid point. He assumes that time is a measurement of a state of transitions, from one point to the next … that the universe is like a puzzle, that is rearranged, and that the period of the shift between each rearrangement is the measure of time. Of course, if this is the case, then the past is, in theory, just one particularly complex arrangement … one that is unlikely, but that could possibly, come again. In addition, there is the possibility that the universe expands, collapses, and then expands again, like an entropy ridden rubber band. [1] If that is the case, then everyone could find themselves traveling to the past at some point in the collapse towards re-expansion. [2] "As Stephen Hawking questioned, if time travel to the past is possible then why have we not experienced time-traveling tourists to our time? Why were there not reports of out of place observers at different historical moments?" Maybe there are, or maybe fears of altering causality have prevented them from visiting in an interactive form. Perhaps they would ‘visit' using self-created temporary micro-universes, existing in a parallel state outside of any sense of dimensions, and of which we are unaware. [3] Who knows? The technology would clearly have to be enormously advanced. Because it is impossible to say that we have been visited, it is best to say that evidence suggests that time travel is impossible. It does not, however, preclude it. "My opponent has already conceded that effecting past events is impossible (by his admission that the grandfather clause does exist)" Careful now – I never stated that the grandfather clause exists, just that even if you use it, it would be irrelevant to the debate. Re: Point 4 "To believe otherwise would be to believe that versions of ourselves live on forever in the past but this is not possible as one thing cannot occupy two points in space at the same time. Since space and time are connected in spacetime, it is not possible for a version of ourselves to exist in the past as well as exist in our present." While it is not possible for two things to occupy the same point in space-time, it is possible for another thing to displace an object in space, as we do whenever we move. Assuming that this displacement occurs as a consequence of our movement through time (albeit forward) there would seem little reason to expect a different result if we went backward. Therefore it is possible for a time traveler to displace, say, past air molecules, but, of course, in doing so we would change the pattern of the past and affect causality. This being the case, we would only experience the past for an infinitesimally small moment before either it branched off into a parallel universe or was altered to a different state than the ‘original' past. [1] http://en.wikipedia.org... [2] http://en.wikipedia.org... [3] http://www.npr.org...