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Is there a reason to believe there is more matter than anti-matter ?

  1. Jan 28, 2014 #1

    I keep reading about that the universe is supposed to be composed of only matter. And that this matter was an excess amount compared to anti-matter after the big bang. So most of the matter and anti-matter annihilated each other and some matter was left over.

    My question is: What is the reason to believe that everything we can observe in the universe is composed of matter ? What is wrong with assuming that a far away galaxy is entirely composed of anti-matter (such that the amount of matter in the universe is equal to the amount of anti-matter achieving perfect symmetry in this respect) ? Anti-matter would appear to us the same way as matter and since it is not globally charged and therefore doesn't attract each other electro-magnetically (which would be the only difference between matter and anti-matter) I don't see any problem with this idea.
    This way the problem of baryon-asymmetry could be completely avoided.
    It turns out in this link there are some explaination and also the one I suggested here. So it seems the only reason not to believe it is that there are no seen sources of gamma-radiation where matter and antimatter come into contact. But on the other hand galaxies are drifting appart making it more and more unlikely for such event to appear. Also if they would touch (like ages ago lets say) they would create lot's of gamma radiation virtually pushing the 2 clusters of matter and antimatter appart, wouldn't they ?

    Any thoughts on this ?
    Last edited: Jan 28, 2014
  2. jcsd
  3. Jan 28, 2014 #2


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    This question has been asked by many people, but there are strong observational arguments against distant galaxies being made of antimatter. Galaxies contain significant quantities of gas in addition to stars. If some galaxies or galaxy clusters were made of matter and some were made of antimatter, then at the boundaries where they meet the matter gas and antimatter gas would be interacting and annihilating. This would create a flux of characteristic gamma rays, and we don't see these gamma rays. So we're pretty confident that all of the galaxies that we see are made of matter. This link gives more detail.
  4. Jan 28, 2014 #3
    from the article:
    Coming up with an explaination to this doesn't seem very challenging: As I suggested as soon as these clouds collide they start to annihilate at the border, releasing huge amounts of gamma-radiation which should push matter as well as antimatter away and therefore separating the clouds (also attractive forces between the clouds would have been merely gravitational as I'd assume atoms/anti-atoms respectively have formed by then). Where is the problem here ? I mean at least this appears more reasonable than changing one of the most fundamental rules that particles can only be created as pairs of particle/anti-particle (as far as I know there hasn't been a single observation of violating this behaviour ever).
  5. Jan 28, 2014 #4


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    You don't have clouds of matter and antimatter, you initially have a cloud that contains both. Before you need a mechanism to not allow already separated clouds to not fall into each other, you need a mechanism that will separate matter and antimatter.

    Plus, your mechanism will be easily observable, see phyzguy post.
  6. Jan 28, 2014 #5


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    There are several problems with what you say:

    (1) The radiation pressure of the emitted gamma radiation would not be nearly enough to "push the gas out of the way". Try calculating it.

    (2) Galaxies and galaxy clusters are in constant motion. In your model, there would be a huge pulse of gamma radiation as matter and antimatter galaxies first interact. Why are none of the matter/antimatter galaxy pairs in the universe in the process of interacting and producing this pulse of radiation?

    (3) It's not true that no violation of matter/antimatter symmetry has been observed. CP violations, which lead to this type of symmetry have been observed. The problem is that the observed CP violation is not large enough to explain the observed matter/antimatter asymmetry. This is called the "Strong CP Problem". But it is probably just that the standard model of particle physics is incomplete, and we have not yet understood all of the CP violating physics.
  7. Jan 28, 2014 #6


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    You need to show how the weak (and we know they are weak) gamma pressure can overcome the much stronger (by ORDERS of magnitude) space-charge attraction between the matter-antimatter. Simply dismissing it via hand-waving argument will not work. This is where quantitative estimates must be made.

    Not only that, you must also show how such isotropic radiation can produce spatial segregation of matter and antimatter. This is neither trivial nor obvious.

  8. Jan 28, 2014 #7
    concerning (1): I'm probably not capable of calculating it, so I'd need to trust your words here. It didn't seem so far off to me because a similar radiation force prevents e.g. the sun from collapsing in which the radiation should not nearly be as great as for annihilation reactions.

    concerning (2): there certainly would be a huge gamma radiation source from this, but I'd think that things have settled by now, so it is not really observable anymore. I mean how often do galaxy super clusters collide now ?

    concerning (3): I'll look into cp-violation thingie...
  9. Jan 28, 2014 #8
    If they have formed atoms there would be no charge attraction, only gravitational, isn't it ?
  10. Jan 28, 2014 #9


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    What do you mean by "now"? When we look out at the universe, the further away something is, the further back in time we see. So we don't see a snapshot in time, we see a whole history, and we can view galaxies and galaxy clusters all the way back to their early formation. We see many clusters in the process of colliding. The Bullet Cluster is one famous example of two colliding clusters, but there are many others.
  11. Jan 28, 2014 #10


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    Atoms form VERY late in the nucleosynthesis of the universe. Unless you have a different revisionist view of the timeline for cosmology, there is a period where you have these bare matter-antimatter floating around due to the high temperature/energy. Why do you think the quark-gluon plasma (or fluid) was so important to create and study at the collisions in RHIC?

  12. Jan 28, 2014 #11
    Ah okay, I wasn't aware we can actually still observe colliding clusters. That sounds like a serious problem to my idea ;)

    Okay, I thought that at such high energies, way before atoms could emerge, particles would have two much energy to annihilate - or better say an annihilation would follow an new pair creation right away.

    Well thank you for your insight and patience with my non-scientificly backed arguments. I think I understood why this idea is unlikely true. :)
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