Rov
The point is that the Universe itself is expanding.
It's not that stars and galaxies are rushing away from the centre of a big explosion - the very fabric of the universe is expanding.
A typical analogy is raisins in a lump of dough - as the dough rises the raisens are all acrried away from each other.
How do we know this?
Well the speed is proportional to the distance. Closer galaxies are receding slower than more diistant ones.
There is more space between the distant galaxies to expand and so they are moving away faster.
This is why it looks to every galaxy as if they are the centre.
What is it expanding into depends on the shape of the universe. We are not talking a simple 3 dimensions here.
It might be flat and infinite or it might be finite but without boundaries
If you imagine a Universe where if you travelled as far as you could in any direction you came back to where you started - that would be a 4 Dimensional Torius (ring doughnut)
A bit like this
http://www.youtube.co...tMu_Q&feature=related