[James C. Bennett]

Someone gave an interesting insight into the problem with time travel.

When you go into the past or future, the physical space around you isn’t still. The universe is expanding, the Sun tugs the Solar System at breath-taking speed into the Milky Way, which too is in rapid motion. One second of time travel implies a change in your physical position to such an extent that you would be over a million miles away from where you were in the “present”.

Interesting, eh?

[SamAdams76]

I've thought of the same thing. Even the rotation of the earth must come into play. For example, if I could time travel to 12 hours ago, my physical location might well be somewhere in Asia (not even considering the variables you just mentioned). So any "time travel machine" would have to also make the necessary corrections for physical location - not only in the universe but for movements in the galaxy, solar system and even the rotation of the earth (and the shifting of continental shelves).

The more you think about time travel, the more difficult and complex it becomes.

[Cboldt]

-- One second of time travel implies a change in your physical position to such an extent that you would be over a million miles away from where you were in the "present". --

Except the speed limit of "c" is on the order of 190,000 miles per second.

Plus there is the relativistic issue of choosing the supposedly stationary frame of reference. How does the time travel machine "know" that?

[aft_lizard]

I think then you should use a spaceship of some sort. With computers we should be able to calculate where in this solar system we would be and what part of the galaxy and what part of the universe, etc. By the time time travel was actually possible that would likely be the best way.

[LibWhacker]

Was watching a show on the Science Channel last week and they made the point that the dimension of time really does have all the properties of the other three spatial dimensions (except for our inability to travel at will within it).

Upon hearing this, I immediately had an “Aha!” moment with respect to the issue you guys are talking about. Of course, a physicist might say it was a “snuffle, chortle, bwahaha!” moment.

But here is my insight anyway, for your amusement:

Gravity doesn’t take a vacation on objects moving in 3-D space and it wouldn’t stop working on us if we were traveling in time either. As long as we didn’t attach a rocket to our time machine, gravity and Newton’s first law would guarantee our coordinates on the surface of the earth wouldn’t change after a trip in our Wellsian time machine and we wouldn’t materialize somewhere out in the vacuum of space.