The way I've always seen it, the 88mph is simply a critical point. below that, there's no action, but when you reach it, everything happens instantly. So at 79.99mph, Marty is in his own time travelling at good clip. And there is no 88.01mph, because the reaction has taken place before that and sent him instantly through time, where he starts to slow down again. The "distance" in time is immaterial, all the energy goes into reaching that critical point, breaking the barrier, so to speak. Once you breach it, you can go anywhere.

As to the Earth being there when you arrive, well there's a trickier question. I have considered it myself, and even considered writing a short story about it once. A kind of "oops, forgot to take that into consideration" story. And you don't even need to give it an hour, considering that we are moving at thousands of kilometers per second. Even a millisecond would be enough to throw us off the face of the Earth.

But then I thought about it some more. It all centers around relativity. The problem all centers around the idea that the jump is discontinuous, that the time traveller keeps his current velocity and vector when he jumps, and so the Earth moves out from under him, so to speak. But then, what is he maintaining that velocity relative to? Is it the cosmic background radiation? The local group? Does he break with everything when he jumps? I have a hard time picturing it, though that's probably just my poor grasp of physics. [img]/phpBB/images/smiles/icon_smile.gif[/img]

So I can see a couple of ways around it. In the first one, when the time traveller jumps, he keeps the velocity connection he has with the universe. He continues to "stay with the Earth" as he moves through time, even though that jump is instant. It's more like an instant fast forward than a discontinuous jump. Although I can see problems with this model too (What happens when an object moves through the space occupied by the moving time machine? Why doesn't the passenger age as well?, etc.).

Or perhaps, and more likely, the time machine itself is able to take the spatial considerations into account as well. You've created a machine that's able to move through time, surely it's powerful enough to compensate for the movements of the universe as well.

In short, it's only a movie. If time travel didn't work ouf in that universe, it would be a very short and uninteresting story (New title: Marty goes Boom!).

Now, let's not get started on the time-paradox question, ok?

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<font size=-1>[ This Message was edited by: David Hall on 2002-07-27 03:00 ]</font>