Chris Ambler, a veteran of the DNS wars, throws cold water on my plans to attend MIT's upcoming time travel convention at a later date to be announced. It seems that I will also need to perfect my FTL transport in order to get back here in a reasonable time from wherever the Earth has gone, cf. Ambler On The Net, An Aside… The Future Is Now… and Then.
On the other hand, I was always under the impression that the light-speed barrier is tied to our inability to travel in time, as doing so could mean that some information had traveled faster than light. Even so, the navigation issue looks substantial.
Which actually brings me to a serious question I've wondered about for years: given the movement of the galaxy, the solar system, our galactic cluster and all the other things rushing and spinning, about how fast is everyone on Earth actually moving relative to frame of the universe's center, if there is one? I suspect that's not as meaningful a question as it feels, given what I dimly recall about theories of expansion of the universe, and the serious possibility that there is no there back there, but I'd like to know anyway.
In one sense, we do travel in time all the time. It’s just that we travel at a fairly constant rate of 1 sec/sec and we can’t alter it too much. And since 1 sec == 10^-6 m, we’re always travelling through time at the rate of 10^-6 m/sec.
There is no center of the Universe or — more correctly — every place appears to be the center of expansion. So the answer is trivially 0. Hope this helps.
Furthermore, there are issues traveling back in time to a time when time travel machines have not been invented. But one thing you have to remember is that for the most part time travel requires travel through space, so targeting a location isn’t too difficult. It just might take some time AFTER you time travel. So yeah, it might take some navigational work to hit the earth as you exit time travel state, but then you just have to find it.
While there is no center to the universe, there is a sensible “preferred rest frame”: the local frame where the cosmic microwave background is isotropic. The earth is moving at around 370 km/s relative to the CMB rest frame. Someone asked “Google Answers” a similar question:
The answer by “eiffel-ga” is pretty thorough.
Have you seen today’s APOD, which reminded me of this question?
Adam beat me to it. Here’s the archive link, in case you don’t look today: