Does an anti-universe exist?
Matter and antimatter aren't 100% symmetric. i.e. CP violation. How is anti-universe, if exists, different from universe?
We posed this question to Professor Andy Parker from the High Energy Physics Group at Cambridge University...
Andy - It seems unlikely. I mean, there's nothing in principle to stop you having a Big Bang that created an anti-universe rather than a universe made of matter. But what we do see is that there is no obvious place where there's a lot of antimatter annihilating a lot of matter. So if you wanted to make an anti-universe, you'd have to separate it completely from the matter one or at the point of contact there would be lots of emission of gamma rays as everything annihilates and we see no such source. So, the idea that there's a chunk of the universe which is all antimatter seems to be ruled out experimentally, at least as far as we've looked so far. Now whether there's an anti-universe hiding down some strange extra-spacial dimension is a completely different question. I'm actually looking for extra-spacial dimensions at the moment, but I don't think anyone is seriously expecting to find an anti-universe at the end of them.