Time travel is possible if it does not come to the awareness of the people of that earlier time in any sort of large way. This is the time travel of the movie 'Freejack' and of 'Millenium'. Steal the person a moment before death, and drop a mannequin in its place to be burnt beyond recognition.
Now one could simply invoke MJ's sawtooth snap, or one could look for another explanation.
Reality is formed by the consensus awareness of the people of a given time. This awareness may be benefitted by verbal or TV communication, but sometimes it is even, if the psi level is high enough, is carried on an unconscious psi carrier wave. Now time travellers vibrate at a different psi frequency so their knowledge of events does not impinge on reality. However, they are able to shape reality in their immediate vicinity.
Thus a time traveller may open a gate on to a train about to derail. Gas all the passengers into unconsciusness, move the passengers to the future, replace all the bodies with gel mannequins, and depart without damaging the time stream. The train crashes, and burnt bodies are found.
Or to put it another way...in this universe if a tree falls alone in the woods, it does not make a sound because it does not exist.
I may have done this one before, if so, oops and oh well.
As I understand it, I really like MJ's theory. It's really just a common sense approach to time travel, once you understand the common sense aspect of it. I don't like it, because there's so many things I'd like to go back and change, and under his theory, I can't do that. Well, I can't do that anyway, so what difference does it make? So you could say I like it in that it makes sense, but I don't like it, in that it makes changing history impossible.
John, you should be more careful in what you say. My theory does not make changing history impossible; it makes it horribly dangerous and unlikely to be beneficial if done intentionally. For example, if you knew you were about to die anyway and you really didn't care about anyone in the universe except yourself, you could look up a few critical events in history--multi-million-dollar winning lottery numbers, clear winners of major sports events, anything on which it is legal to place a bet--then take that information back to your younger self and make him rich. You cease ever to have existed in that form, but instead he lives to be a wealthier version of you. It is almost impossible for him to make the same trip at the same time for the same reason, so he will cease ever to have existed at the moment he should have made the trip, and your history is restored only to revert to his--but you won't care, because in one of those histories you approach death believing that you've given yourself a shot at the good life, and in the other you're living that life. The rest of the world never advances a moment past your point of departure, but you never actually die, either (unless you die in the history in which you made yourself rich, which would be bad luck, really), and most of us are pretty sure that John would not be deterred from the possibility of giving himself that better life by something as unimportant to him as what happens to the rest of the universe.
Maxx, I have already looked at the problems in Millennium. To quote from that page,
To suggest that the universe has not changed merely because humans existing at the time don't know it has is extremely parochial and anthropocentric, not to mention foolish.
That's how I feel about your notion that the universe is whatever people believe it to be. I know that's a popular notion in New Age spirituality, and let me try not to offend anyone's religious beliefs here, but even on a six-day creationism view the universe existed as what it was without humans for a few days, and on a modern scientific view those few days were measured in increments that put centuries in the same class as seconds. The universe might also continue after the human race departs.
Further, if we assume that you are right, that the universe is what people believe it to be, then we need not go back more than a couple thousand years to a time when the stars and planets were supernatural beings--angels or gods--dancing on a glass-like floor that was the ceiling of the world, in which was stored great quantities of liquid water occasionally released as rain above the flat surface of the human realm. That describes the majority view of the universe as seen by our ancestors. It is different now. Now we believe that the stars are huge fusion reactors spread across unimaginable distances in a vacuum called space, and that rain falls because warm air holds it as vapor but cool air cannot hold as much so the gas liquifies and drops out of the air. According to your description of how reality works, it now really is like that because we came to believe it to be like that. The problem is, we came to believe it to be like that because some very intelligent people looked at it very closely and observed aspects of it that were inconsistent with what everyone already believed--and then at great peril to their own lives, they announced that everyone was wrong in their beliefs. It would not be possible for the world you describe to be such that everyone was wrong in their beliefs about it; whatever the majority believed to be true about the world would be what observation would demonstrate. Thus once the scientists started examining everything, they would announce that indeed the stars were heavenly beings involved in a complex dance above the shell which held back the water until the windows were opened to allow the rain to fall.
So without even beginning to think about the ramifications of someone forcing his own distinct perception of reality on his own corner of the universe, I have to exclude that description of reality that is necessary for it to work.
Now, I'm not averse to a universe which does work that way. I'm under the impression that the World of Darkness works that way, and that to be a Mage is to learn to impose your own opinion on reality. In such a universe you could alter history by imposing your beliefs about it on that history; but then, in such a universe either the stars are dancing angels and the rain is held back by the windows in the dome of heaven, or someone at some time had a probably nefarious reason to alter the reality in a huge way to make it fit a theory no one else alive had ever begun to imagine.
--M. J. Young
John, you should be more careful in what you say. My theory does not make changing history impossible; it makes it horribly dangerous and unlikely to be beneficial if done intentionally.
Which is more what I meant.
I wouldn't time travel to make myself rich. I'd go back and beat the living daylights out of some people. I wouldn't hurt them too badly mind you. If they were lucky, they might only spend a week in intensive care when I was finished. The result is the same though. Infinity loop.