Ok, I have a question concerning one (rather important) aspect of time travel I don't recal anyone really discussing; the Earth. Or what I'd like to know is how do we get there (forward/backward) from here...our current spacetime coordinate at the point of departure? With the most popular theories of time travel we're talking about either intersecting with another timeline (alternate reality) or actually moving backward/forward along the current timeline. However, regardless of which ever mode you want to consider, is the traveller actually physically relocating to another coordinate in spacetime? Whether you're talking about alternate realities or not, the Earth in any reality is still moving through the universe on a fairly predictable (that is if we knew how to plot it) course. Let's pause for a moment on whether or not we'll be able to travel forward/backward in time, if you take all the movements the Earth is involved in (revolution, precession, solar precession, galactic revolution, and galactic precession), let's say for simplicity's sake a sort of loopty-loop trajectory through spacetime. Wouldn't it be fair to say that time travel is rather like arriving on the Earth at some predetermined spacetime coordinate? If your object is to go back, then wouldn't your destination be some spacetime coordinate the Earth has already crossed, and how could you win such a race that has already been won? Or alternative going forward in time would equal a coordinate the Earth has yet to cross, and would you be hanging out there in space waiting for you're future Earth to catch up with you? So there you have my quandry, if anyone or perhaps Dr. Kaku would like to tackle it, I'd sure like to know someone else's opinion.