All of the "theories" on time travel that I have seen in this forum are sadly lacking any originality. The very first lesson of time travel is that time is field dependant. Time outside our universe flows at a different rate than time within our universe does. Next, the big picture. As our universe expands, so does the change in it's temporal constant. In other words, the rate of flow of the time stream today is different than it was five billion years ago, and is different than it will be five billion years from now. Next, when considering the possibility of time travel, the potential traveler must not only consider temporal coordinates, but spacial coordinates as well. For unlike the Sci-Fi version of time travel, where the entire universe would have to go backwards in time. A single subset of the universe will not affect the whole, therefore while a time traveler may change his temporal profile and appear in the past or future (relatively speaking) the rest of the universe has/or will move move onward. So not allowing for the combined motions of the universe might find the traveler inphasing into something solid or simply floating in space. Next, the ludicrous time paradox's (nothin' funnier.) The hubris that the universe would care if the time line as altered is staggeringly hillarious. First, for someone to go backwards in the temporal stream and create a causality effect that would affect them later, thereby preventing them from initiating the causality effect in the first place shows a gross lack understanding in temporal mechanics. For this to happen, the temporal stream for the entire universe would have to be looped back in on itself creating a bigger mess than "What if I shot my grandpa?" would ever make. By the way, in case you were wondering, for the time traveler it dosen't matter if the timeline is changed, since indirect personal causality no longer applies after leaving the time stream. Which also brings me to another one of my favorites, "Time travel can't be possible or else we would have been visited by travelers." Since changes in the timeline don't affect the traveler indirectly, they become free agents to change whatever they want in the localized temporal stream, and you would never know it. They could be all around you, and since they have no great fear of causality, a time traveler could be a co-worker, a student, a neighbor, someone walking down the street, in fact a time traveler could be anywhere doing anything and again you would never know it.