What prompts me to write this is all the conjecture about time travel. Shouldn't we be a bit more down to earth about all this? All too many of us seem to generate concepts that are not even suggested by the original theories ... especially matters dealing with relativity. Remember all the baseless conjecture inspired by the Heisenberg Principle? It's still happening. The only way to go back in time is to reset all particle positions and motions within a given range to some previous state. The interactions will then sequence in the same manner as they did originally. Time as we know it will repeat. A problem occurs with edge (or surface) deterioration because of particle influence outside the given range, and this may corrupt the original sequence. This could also create an initial coflict of particles. And, particles actually entering the range from outside may corrupt it. Thus, unless the given range is inclusive of the entire universe, exact re-sequencing cannot be guaranteed. For ranges smaller than the unverse, the larger the range of reset, the longer the time required for corruption to occur. We would still be restricted to the speed of light, and this poses a limit to the range of initial reset. Obviously, to travel into the future requires that we know all the future particle positions and motions. By the way, none of this as far as I know is supported by any established theory.