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[Anti] Matter In The Early Universe - Over Complicated?

  1. Mar 27, 2009 #1
    Is it possible that particle physics is over complicating theories about why all the matter in the early universe didn't annihilate, even though equal amounts of matter and antimatter existed? Is it possible that inflation happened quickly enough that antimatter and matter were blown clear of each other, and were too far away from each other to re-attract and annihilate?
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  3. Mar 28, 2009 #2
    Yes, there are peculiar models in which matter and antimatter repel each other. There are even models in which matter attracts antimatter but antimatter repels matter. Many ideas, all speculations... Why would you need them if the standard model tells you there must be an asymmetry between what we call antimatter and matter ? Is it not to best investigate whether simple things which we have established can explain the observed asymmetry ? Although we do not have a general agreement on what produced this asymmetry, there are already many models predicting it without modifying fundamental principles. In any case, exotic scenarios are investigated as well, such as scalar-tensor gravitational theories, although there main motivation is not matter-antimatter asymmetry.
  4. Mar 28, 2009 #3


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    I don't see how this would explain what we see today. If they didn't annihilate, then where ARE the other half? These antimatter of equal amount to our matter should still be around and should be plainly observed. We know how to detect them, and we can detect signatures of their presence. There should be planets made of them the same way we have for matter.

    So where are they?

  5. Mar 28, 2009 #4
    How do we know that say, a distant galaxy is not anti-matter? (I'm not suggesting that one is at all, just wondering what detection matters we actually have) Neutrino emissions from beta decays that shower us from that direction? I can't think of much else, maybe pion +- shower ratios or other particle shower rations from known stellar/galaxial reactions.
  6. Mar 28, 2009 #5


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    As we look around us, we see many galaxies interacting with one another, including collisions that leave one another tidally distorted. If an antimatter galaxy (with intergalactic antimatter dust and gases) collided with a normal galaxy, we'd be in for a pretty big show. The absence of such observations suggests that either antimatter galaxies do not exist or (highly unlikely) that they repel galaxies made of normal matter. Experimenters at CERN intend to test the Weak Equivalence Principle using cold neutral antihydrogen to determine if the gravitational infall rates of matter and antimatter are the same. If the infall rates are not the same, that would be an interesting result.
  7. Mar 29, 2009 #6

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    It is possible that there are antimatter galaxies very far away, and the sort of interaction that Turbo-1 describes is hard to see because it gets swallowed up in the diffuse x-ray background. However, in such a case we would expect to see anti-helium and anti-iron nuclei in primary cosmic rays, and every such for them has come up empty. These are the most stringent limits we have.
  8. Apr 13, 2009 #7
    The PAMELA satellite experiment (Payload for Antimatter Exploration and Light-nuclei Astrophysics) recently reported a measurement showing that the anti-proton to proton flux ratio in cosmic rays is about 2 x 10-4 .
    See attached PDF.

    Attached Files:

  9. Apr 13, 2009 #8

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    Antiprotons are not anti-helium or anti-iron nuclei.
  10. Apr 14, 2009 #9
    Correct. No antihelium was seen. In fact the antiproton yield (see my reply #7) is consistent with antiproton production by very high energy (mostly ordinary proton) cosmic rays colliding with interstellar gas. So no real evidence for antigalaxies yet.
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