[chicagobob]

Something I've always wondered is -- of course going back in time is a bad thing -- but is going "faster than light" necessarily going back in time? I wonder why, say, instantaneous communication across the galaxy wouldn't be possible, as long as it doesn't go back in time. (BTW: not necessarily from a physics point of view, they would say that not only can't one travel back in time, neither can you go faster than the speed of light, but I was wondering more from a paradox / time causality point of view).

[hugh3]

See my comment elsewhere in this thread, but the answer is yes but I can't explain why in anything shorter than an entire textbook on relativity. If you've "always wondered" about this, then this is the universe telling you to go and learn relativity (at least special relativity).