[sometimes]

Aren't we waiting for the light from the other side of the visible universe outer limits to reach us, consequently we can't know what's out there for certain. Also if the universe is expanding, it seems sensible that matter on the outside is moving fastest away from us, (hence red shift?), there must be a point where matter is travelling so much faster than us we can't see it as it's travelling at the speed of light?
We can move backwards and forwards in three different dimensions, unfortunately we can only travel through time at a constant rate in one direction relative to us as individuals, not necessarily each other.
Of course there is no 'before the big bang' since time didn't exist before it.

A supplementary question, has the centre of the universe been identified? If so where is it?