Originally Posted by Guy Westcott

Yes, gravity affects time. Every object with mass pulls space time towards it (relativity, I think). This means that the more gravity there is the faster time travels, so if you go near a black hole and stay there for 5 minutes you could return to Earth 40 years after you left. This is why air-hostesses live longer, because they spend so much time away from the centre of the Earth, that time travels slower for them, so to everyone else they have a slightly longer life.

I believe time IS a dimension, exactly like the first three, and as such can be travelled along, forwards and backwards, but as a species we are unsure of how to do this. We can travel forwards in time, easily, just by going away from the Earth's core. Even jumping 1cm in the air effectively send you forwards in time, but only by an infintely tiny ammount. I also think that the idea about an object that has a limited fourth dimension is perfectly plausible.