A question about time travel and earth's location

I tried to search before posting, but there is a fatal error message coming up. Anyways, if time travel were suddenly possible tomorrow and I wanted to go back to 1972, wouldn’t the earth be in a different location than it is today as opposed to my “landing date”? Wouldn’t that cause the time traveler some problems? I’m sure this has been discussed, right? I would wikipedia it, because I’m sure this theory has a name, but what?


Obviously, you need a “Space Time Machine.”

I have to tell you, though, among the things wrong with real time machines, this one is just windage.


Well, it makes sense at a cursory overlook. If you go back in time 12 hours, you should be on the opposite side of the planet, since it moved while you didn’t. And if you go back six months, it should be on the opposite side of the sun with you floating in space.

But… The sun moves. The galaxy moves. Everything moves. What are you staying stationary with respect to? You can’t say “space” because of special relativity. So, any one thing is as good as anything else. You might as well say you’re stationary with respect to the Earth.

Yabbut, if anyone actually invents a genuine time machine, SR is right out the window, innit?

Reminds me of an old Superman comic, with this incredible loser villain, a punk kid who had found some magic amulet that let him just ask people for whatever he wanted and they had to give it to him. Supes managed to get him in a headlock, but the kid asked politely for Supes to just stay still and let him go, or something, and Supes decided in the process of complying to parse the statement into its separate parts, and remained absolutley motionless until the earth had moved far enough in its orbit that the atmosphere began to thin out and the kid passed out.

God, I really need to get a life.

The movie Primer offers an interesting solution to this common problem of time travel science-fiction — which is usually ignored otherwise.

In the film, the time machine is a container for a field, or volume, that is segregated from the rest of the universe. Objects can enter and exit the field at either end of its duration, the interval over which the machine is active. So, although you’re able to travel backward in time, it’s only to the moment when the machine was last turned on in the past, and the field was established. Also, it’ll take you a lousy one minute per minute to make the journey — so if you’re travelling back to a week ago last Tuesday, you’d better pack a really good lunch or two. And bring a sleeping bag.

Anyway, the “Earth moving out from under you” problem is solved, fictionally, by having the time traveller contained in the machine travelling backward, while the time machine is an otherwise ordinary object sitting in normal space-time, travelling forward.

While travelling forward in time, I find myself under the influence of a force named “gravity,” which tends to keep me relatively glued to the surface of the Earth.

Why should this force stop working when I am travelling backward in time?

(Well, maybe there is some reason, I don’t know.)


I don’t see why it would be. Lots of things which seem to be common sense do go out the window, but relativity isn’t one of them.

Back to the OP, many time machine designs are based on a spacecraft following a particular trajectory, and ending up at the end of that trajectory at an earlier time than at the beginning. Where you end up is then just a function of what trajectory you followed, just like with normal, non-time-travel trajectories.

You might be conflating two Action Comics stories from 1980. Issue #508 was the second of a two-parter in which a one-shot leftover hippie character named “Starshine” has been imbued with the powers to compel anyone to do anything as long as he adds “Please”. This was actually a minor subplot in an otherwise outstanding (and I believe award-winning) story called “The Miraculous Return of Jonathan Kent”. Superman foils him by using a robotic gag that locks itself around his mouth and the subjecting him to super-hypnotism compelling him not to use his powers again.

The next issue pits Superman against a small group of “space skeptics” that are aggressive conspiracy theorists about NASA missions and even deny Superman’s own well-publicized alien origins. It turns out they’re aliens themselves who crashed on Earth some decades earlier and, depressed about being marooned on this backwater rube planet, subjected themselves to hypnotism that made them forget their true origins as well as making them doubtful of space travel generally. Unconsciously, their mental powers are creating a yellow phantom that begins attacking NASA launches, which is what draws Superman’s attention. The phantom gets Superman into a powerful armlock and holds him, since both know that the phantom will fade if it gets too far from the aliens. Superman holds himself “perfectly still” and Earth, in its orbit, casually moves away from them, to the same effect.

I didn’t even have to leave my chair to dig out my comics. I did a search for Action Comics covers, found #508 and #509 here and typed up the summaries from memory.

I sneer at your novice geekery, grasshopper.


:: bows ::

You just have Jordie punch a subroutine into the Hiesenberg Compensator then hook it up to the deflector array.

What, without reversing the polarity of anything?

Reverse polarity only in the southern hemisphere.

You don’t move. The shifting of a person in time involves the fabric of time space being folded and unfolded around you to where and when you wish to be. It is as easy to be when and where you wish to be as to not be. This is all thanks to the spice Melange found only on the desert planet called Dune. It is by will alone that I set my mind in motion.

Jeez, Bryan, if you’re gonna ride my ass like that, at least pull my hair.

Seriously, though, you hit the nail on the head. That’s exactly what I did. I must have read those two back to back late one night and fused them subconciously.

You’d have to preserve your momentum, so if you were not subject to gravity you’d have to go shooting off with the velocity you had when you turned the time machine on.

If time travel worked by little jumps, where you’d be under the influence of gravity between time jumps, then it wouldn’t be an issue.

I’d time travel in a spaceship myself.

No problem. Looking over that set of covers, I think I can pretty much summarize from memory almost all the ones in that set (with a few rare exceptions that for some reason I didn’t buy at the time). In 1980, I was flush with paper-route money and the comics were my main entertainment. When DC upped the cover price to 50¢, in September of that year, I was at least impressed by them adding 8 pages of material. Unfortunately, the inflation continued, eventually causing the demise of the dollar comics and dollar digests.
Hmmm, I think I likes me a comic-book nostalgia thread in CS…

Modified tachyon pulse/beam. That solves everything.