[Guille]

The universe can't ahve a centre because that would mean there is a point of reference and so the whole work of relativity is partly wrong (at least is wrong in all events including an observer in the centre of the universe, but even in those events not ioncluding it, as some are in perpendicularity with the point they might also have to change in theory). Actually, the universe miht have a centre, but if it has one we must re-invent special relativity. No obsevations have reached far enough to tell if there is a centre or if a tall the universe is spherical.