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Time isn't a "thing" that actually exists, it's a measurement. Time is another way
of measuring distance: how long does it take to get from here to there. Once we have
devised some unit of measurement, a mile for instance, we can then figure out some way
to measure how long it takes to cover that distance by devising units of time.
What we're measuring is distance as a variable. We start here, move, measure how far
we've gone and then calculate how long it took. The measure of distance is
real because we have reference points, the measure of time is wholly artificial and
arbitrary. Time is a product of the human mind that has no corresponding object in
reality, kind of like unicorns.
Any measurement of time is one of duration and that only makes sense to entities making measurements (us). A point in time is really a point in space. Since space has been expanding since the Big Bang (see This) so every point in space has likewise been expanding. The effect is that everything keeps getting farther apart. The distance between objects is greater now than it was at any earlier time. Time is only another measurement of that change in distance. To experience some earlier configuration of the universe, we don't really travel through time; we have to move into space that no longer exists. Since the Big Bang would've accelerated everything away from the initial point of its expansion, the only way to experience an earlier configuration would be stop or reverse that acceleration. If any point in the expanding space could be frozen in its motion relative to the absolute motion of the expanding universe, it would also stop time. If that point resumed it's motion, the time since it stopped until it resumed its motion would be how far back in time it had traveled. Time travel is movement through space. Since space itself is moving, time travel is only possible by stopping movement relative to the expanding space. To get to some particular point in time, one must also know where in space that time was at that time. Merely stopping motion in relation to the surrounding universe isn't enough in this case. It will also be necessary to stop one's motion, in a particular direction! This mean a kind of negative acceleration. One would have to calculate every motion for the entire history of the time since the event in question. It's like unraveling the exact path through the accelerating space and then reversing that path back to the time one wishes to visit. Time travel is just another form of space travel. The calculation to accomplish all this will be hugely difficult since the various motions through space of any object are subject to all manner of influences (see This). It should be obvious from all this that there are no time-paradoxes possible in time travel. Since one can only access some earlier time by a kind of anti-acceleration through non-existent (or at least, no longer existing space), it follows that the current existing space will not exist in the time traveled to. Whatever changes a time traveler makes will create a new future that will exist in parallel to the time he came from. These futures will exist in completely different regions of space and time, each inaccessible to the other. For a time traveler to return to the time he (or possibly, she) came from, it will be necessary to not only match the speed of the acceleration of the universe in current time (the past), but to exceed that rate of expansion. Since at any one instant in time and space the rate of expansion is at the speed of light, the time traveler will have to exceed that if he (she) is going to return to the space-time he came from. Traveling into the past may be possible but getting back again probably isn't since it requires moving into space-time that doesn't yet exist. Once in some past time, the time traveled from becomes the future which can only be reached by exceeding the speed of light. A "worm hole" (a straight line through curved space) might work if you can find one (see This). |
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