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What percent of baryonic matter is antimatter?

  1. May 30, 2007 #1
    What percent of baryonic matter is antimatter?

    I am well aware that DM accounts for most "matter" and that there was baryon number violation and cp violation to explain the presence of matter over antimatter, but based on theory and observation, what percent of visible matter is predicted or observed to be antimatter?

    I am well aware that matter-antimatter collision are highly energetic, nonetheless if the two are kept separate, they would be indistinguishable from a distance.

    Are there stars, suns, planets, galaxies made of antimatter?
  2. jcsd
  3. May 30, 2007 #2


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    In principle there could be suns etc made of anti-matter since as you say they are indistinguishable from a distance. Observational then I don't know that we could answer the question you ask.

    In terms of the standard model of the history of the Universe I think we could all but rule out their existence from theoretical arguments however. It might seem reasonable in the universe we see today that an anti-matter galaxy could exists since it is spatially separated from other galaxies and hence would not suffer matter-anti-matter collisions. However if you run the clock backwards you find that the material that makes up that galaxy was once upon a time in thermal equilibrium with material that today makes up other galaxies, and hence would have suffered such collisions.

    If there were large domains in the early universe made up of anti-matter then in the boundaries between these and matter regions would be depleted of matter and hence be large scale inhomogeneities, which we do not observe.

    The hypothetical epoch in the very early universe where the matter and anti-matter destroy one another leaving a tiny amount of matter due to a slight symmetry break is I believe in the first fraction of a second of the universe or there abouts. The Universe then remains in thermal equilibrium for the next 300,000 years giving plenty of time to destroy via collisions with matter any anti-matter regions.

    Therefore as I say from the standard model theoretical arguments suggest that there should not be anti-matter galaxies or stars. It would be really nice to test this, since we should never trust theory completely, though as you suggest anti-matter galaxies look identical so I'm not sure how we could ever do this. If the matter/anti-matter symmetry break were to subtly change some spectral pattern that you would expect then this could give us something to work with, but I'm not aware of anything that suggests this would be the case. It would be nice though!
    Last edited: May 30, 2007
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