Time Travel Troubles

Why time travel is unlikely to ever be seen outside fiction

What am I talking about? Well, if we consider time to be an additional dimension in which we can move, then our biggest problem when moving in that dimension is dealing with the energy we have invested in our current motion.

Let's take an example. Say you're travelling along in a train, and you decide to travel 5 seconds into the past. You slip backwards, maintaining your physical position and motion. Suddenly the train you were riding on is 5 seconds back down the track (it's a short train). There's no train underneath you anymore, so you tumble to the track, at whatever speed the train was travelling at, quite possibly breaking a few bones as you land on the track. As you lie there, dazed and hurting, the train catches up and runs you over.

Or does it? Hang on a minute, the earth is rotating, remember? In five seconds, you would move westwards slightly more than 2 degrees of longitude. (Or to be more precise, the planet will not have rotated that far.) That's a substantial distance, unless you're very close to one of the poles at the time. Let's hope the ground where you land is at the same elevation, or you could end up in mid air or buried in rock.

No, wait, Earth is rotating around the sun, too, pretty fast, by all accounts. Where would that put us? If we're on the trailing edge, and we move back a sufficiently small period of time, that could put us in the center of the world. More likely, though, we'd be out in space, trying real hard to breath, and worrying about getting one hell of a sunburn on one side.

Then again, perhaps we wouldn't have to worry about the sunburn. Since the whole solar system is rotating around the center of the galaxy, a 6-year time travel might leave us more likely to get an alpha-centauriburn, but then since our entire galaxy is moving as part of our galactic cluster, and the galactic cluster is part of a continually expanding universe, the chances are pretty good that our eventual position would just be out in the middle of nowhere.

And I'm not talking about "Back of Bourke" type nowhere, this is real nowhere, the kind where all you can see, in the short period of time before you suffocate, freeze and/or explosively decompress, is a bunch of distant galaxies.  Suddenly, travelling in time doesn't sound like such a good idea.