• Question: How do we know that, in the Big Bang, antimatter and matter didn't go off at different directions and that we are just living on the matter side?

    Asked by eigenvector to Arttu, Ceri, James_M, Monica, Philip on 20 Jun 2011.
    • Photo: James M Monk

      James M Monk answered on 20 Jun 2011:

      We don’t know for sure, I guess, but we have good reasons for thinking that could not be the case. The main reason is that there would be regions where the matter and anti-matter overlapped, which would be producing a lot of gamma rays that we could see.

      Maybe it might be possible to construct a model in which all of the anti-matter was swept beyond the visible horizon during inflation, but that would be a very weird model.

    • Photo: Arttu Rajantie

      Arttu Rajantie answered on 20 Jun 2011:

      This is an interesting question. The problem with matter-antimatter asymmetry in the universe is that our universe seems to contain only matter, and practically no antimatter at all. In the early universe there would have been a lot of both, and when the universe cooled down they annihilated each other. There must have been just a little bit more matter than antimatter, so that it was left over when all antimatter had gone.

      The idea that overall there is the same amount of matter and antimatter in the whole universe, and our universe just happens to be in a region with matter excess is an interesting one, and detailed models of this type have been studied. Currently we do not know enough about the law of nature at very high energies to know for sure what the correct explanation is, but hopefully the LHC will help us with that.

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