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”.
The more you think about time travel, the more difficult and complex it becomes.
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?
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.
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 doesnt take a vacation on objects moving in 3-D space and it wouldnt stop working on us if we were traveling in time either. As long as we didnt attach a rocket to our time machine, gravity and Newtons first law would guarantee our coordinates on the surface of the earth wouldnt change after a trip in our Wellsian time machine and we wouldn’t materialize somewhere out in the vacuum of space.