Some people think it is infinite other people think that it our universe is just part of it perhaps one small bubble that burst out of somewhere else a little scum on the bath of infinite universes. Other people think our universe is not big, (not really, really big) but a hypercube or hyper something else and if you move far enough you will see the back of your head going the other way. Or maybe it all ends in a mirror, all round us, that just makes it look as though it goes on for ever like those lifts with mirrors all round where you can see how bad you look from the back.
In our world of three dimensions of physical space:
- up/down
- left/right
- forwards/backwards
http://en.wikipedia.org/wiki/hypercube
Multiverse