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.
@monozuky asked the Naked Scientists: Matter and antimatter aren't 100% symmetric. i.e. CP violation. How is anti-universe, if exists, different from universe? What do you think? @monozuky, Wed, 19th Jan 2011
It depends on how universes work overall and why the asymmetry exists. Lots of people would like to know the answer to that one. In general it is expected that antimatter will have very similar properties to matter and serious attempts are being made to measure the detailed properties of anithydrogen atoms which can now be made and stored briefly in small numbers. Any small deviations in properties could be very significant. Soul Surfer, Wed, 19th Jan 2011
We may not see the annihilation boundary since the matter universe is very vast. The anti-universe existence shall answer the problem of missing antimatter after big bang. It shall have an analogy to the electric-magnetic fields. If at all we encounter the anti-universe we may annihilate and it shall remain undetected. just, Fri, 29th Aug 2014