(Fair warning: There's no real, hard physics in this. It's just a thing I thought of, thinking about time travel, because, you know, that's a thing I do sometimes.)
Time Travel sounds like a good idea, right? You step into a box, that box shifts to a time that is different from this time, presumably at a rate other than the usual one second per second rate of time travel we have so far enjoyed. Right? And then, you step out of the box, and what?
Well, think of this: Let's suppose you have magic technobox that will transport you one minute into the past. OK, not hard to imagine. Sounds good, maybe even easy. So, you step into the box, you set the controls, and the box moves only through time, sixty seconds ago. You step out of the box, and into the airless void of space, right? Because the Earth is sixty seconds ago. You hang, suspended outside the box, and, if you took a pretty deep breath and have good sunscreen, you could then watch as the Earth slams into you at about 67,000 MPH.
Oh, wait, you say. That's not nearly fast enough. That's just the Earth's velocity relative to the sun
. By moving back in time, you get to worry about being slammed at the Earth's velocity relative to Everything,
maybe?. Well, sure, but that number is much harder to find, what with it having no meaning from my point of view, on Earth, and what with it not actually being possible, so far as I know, to stop entirely, relative to the Universe, and things all having different velocities, and so stopping relative to them meaning different things, but the point
is, you'd get sixty seconds of triumph followed by a very short career as ashy paste, wouldn't you?
So, does moving backward in time mess with your velocity relative to the sun (or to any other given point of reference)? It seems like there would be two answers: yes and no. If yes, you'd be slammed more softly, so yay for that, although the out in space thing is still a problem. If no, then the above scenario, paste, etc.
So, if no, and you maintain your original velocity relative to Earth, what if you travelled forward in time just a little? Maybe two seconds, instead of the usual one? Wouldn't that put the Earth, moving at just under 30 kM/S, about 30 kilometers further along than you? So, you'd be thirty kilometers back on the orbit of the Earth, which has a very small chance of being OK, and a huge chance of being very uncomfortable, and occupied variously by rock, magma or nothing at all. You would, though, not be paste. You'd just be, potentially, a little bit dead.
That's my thing. Time travel sounds like a blast, but unless we simultaneously develop non-spacial matter transportation and very, very smart computers, it doesn't seem practical, if only because we are, more or less, standing on a ship, moving at ridiculous speed. It's a big ship, but it's still going really fast.