Apparently, and I don't really understand this, a Russian scientist claims time travel could indeed be possible! He says we might be able to cross the galaxy in an instant without breaking the laws of physics. He believes there are natural 'wormholes' in space, created by the tremendous forces after the 'big bang' and that these could act as shortcuts across the cosmos. It's all a bit beyond me but if it is theoretically possible, then presumably other civilisations could be using this 'galactic subway' to visit us. Just a thought.
If you dispense with
the distinction between space and time, as required by Einstein's theories,
and think of them as a single continuum called space-time then this makes
more sense. There is nothing to dictate that space-time should be flat
- it could be folded. Imagine a piece of paper with an ant in the exact
centre of one half who wants to get to the exact centre of the other half.
If the paper is flat then he (or she) has no choice but to walk half to
the length of the paper to the destination point. However, if (a) the
paper is folded in two (with the ant on the outside!) and (b) a kindly
(book?) worm has bored a hole right through both sheets then all the ant
has to do is walk the short distance to the wormhole pass through to the
other side and then walk the short distance to the destination point,
thus saving him (her) self a lot of travel. If, instead of paper, the
sheet is composed of space-time then 'the other side' could be anywhere
in the universe, at any time, depending upon how the continuum is folded.