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Antimatter's role in the architecture of the universe

  1. Oct 8, 2009 #1
    An airport. A plane to catch. A magazine with an eye-catching cover. A quick flip through the pages then off to the plane. All the elements were there for a deep and critical understanding of the role of antimatter in the formation of the Universe. Or not.

    The facts as told by the journalist.

    Matter and antimatter formed in equal quantities.
    Some of it was annihilated pretty swiftly, but by no means all.
    The matter, clinging together by gravity, formed the long tendrils of galaxies, dust clouds, and stars.
    The antimatter, shunning gravity (the anti-apple falls upwards), spread out to create the immense voids, pushing the matter into large scale web-like structures.
    This was supposed to explain inflation, the large scale structures in the Universe, and the difficulty in locating the anti-matter.
    It was also supposed to remove any need for dark matter and dark energy.
    Nice shopping list.
    Is this yet another journalist on science-inducing steroids or is there any physical basis for what I read in 30 seconds?
     
  2. jcsd
  3. Oct 8, 2009 #2

    Wallace

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    No. Anti-matter behaves exactly the same way as matter in relation to gravity (the apple still falls down). We understand the origin of the web-like structure of the Universe, and it is not caused by anti-matter.
     
  4. Oct 8, 2009 #3

    DaveC426913

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    False, as Wallace points out.
     
  5. Oct 8, 2009 #4
  6. Oct 8, 2009 #5

    Vanadium 50

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    This is not known. It's not excluded that some galactic clusters/superclusters are matter and others are antimatter.

    This is not correct.
     
  7. Oct 8, 2009 #6
    There is more matter (p+e-) then antimatter because of CP violation (Sakharov mechanism if I remember correctly). So you suggest that parameters of the Standard Model, like CP violating phase, vary from place to place????????????
     
  8. Oct 8, 2009 #7

    DaveC426913

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    Elsewhere on PF it has been argued that there would be some pretty stong evidence if there were other systems made of antimatter, notably:
    - a lot of hard radiation at the matter-antimatter interfaces, and
    - Earth-based detection of anti-matter cosmic particles.

    While it's not ruled out, I think we agreed that it would be pretty difficult to swallow.

    OK, maybe not completely destroyed. Any and all contact would result in annihilation and release of gamma radiation. On a grand enough scale with enough mixing, we'd have a universe where there's be lot of gamma radiation and little matter.
     
  9. Oct 8, 2009 #8

    Vanadium 50

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    The CP phase in the CKM matrix is too small to generate an asymmetry as large as a 100% matter universe would suggest.
     
  10. Oct 8, 2009 #9

    Vanadium 50

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    The annihilation radiation at the interface gets lost in the diffuse x-ray background if it's sufficiently distant. ~100 Mpc sticks in my mind as a ballpark estimate.

    Earth-based detection of anti-matter cosmic ray particles is worthless. You get antiprotons, but these can and are produced in hadronic showers in the upper atmosphere. You need to see antinuclei, and there is presently only one measurement I am aware of that went into space to do this: AMS.
     
  11. Oct 8, 2009 #10

    DaveC426913

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    Whether or not it is easy or hard to do, it is my understanding that, generally, scientists are agreed that there are not large quanitites of anti-matter out there, that there are not whole galaxies made of antimatter.

    Are you claiming this is not the general understanding?
     
  12. Oct 8, 2009 #11
    it is too small so it creates only a small disbalance of matter over antimatter (about 10^-8). So it is small but big enough to create the matter we see.
     
  13. Oct 8, 2009 #12

    Vanadium 50

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    Yes. I am claiming, in fact, that the whole motivation of the AMS experiment is that we simply don't know if there are distant antimatter galaxies.

    Now, I would expect people to be surprised if it was discovered that there were antimatter galaxies. But not shocked.
     
  14. Oct 8, 2009 #13

    Astronuc

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    I believe the idea behind AMS was to get above earth's atmosphere in order to remove the antimatter which is generated in the earth's atmosphere by virtue of high energy proton-proton collisions. This way, the detected antimatter in theory has extra-galactic (outside the Milky Way) origins.
     
  15. Oct 8, 2009 #14

    Wallace

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    Vanadium, sorry but your hypothesis would violate any kind of Big Bang scenario. The early universe (say the first few hundred thousand years, before and including re-combination) was extremely homogeneous, so it would not have been possible to have isolated, separate matter and anti-matter regions. If some region was made of only antimatter, the boundary between it and the bordering matter part (bearing in mind that the Universe is quite dense at this stage) would have annihilated, leaving a gaping hole and leaving a tell tale sign in the CMB (as observed by WMAP and other probes). The pre-recombination universe was opaque, so the extra inhomogeneous heating that would be produced in such a scenario would have resulted in a markedly different anisotropy power spectrum. That is before you try and explain why CP violation varies with space...

    As Astronuc pointed out, the anti-matter thaT various missions have been looking at recently is that made in high energy processes in stars and AGN. This is not 'primordial' anti-matter, but trace amounts produced by astrophysical processes.

    You're going to want to provide some references if you want to keep speculating on your personal theory ;)
     
    Last edited: Oct 8, 2009
  16. Oct 8, 2009 #15
    If one matter particle were to come into contact with one anti-matter particle , they would annihilate each other instantly. I probably should have said our universe as we know it now would not exist , for radiation rather than matter would make up all or most of the universe just like it did at the early stages of the big bang , when there was equal amounts of matter and anti-matter.
     
  17. Oct 8, 2009 #16

    Vanadium 50

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    Actually, it's not. I've been trying to trace back to the first papers that point this out, but it seems like it was so obvious, nobody bothers to cite it. As far back as Cohen, Kaplan and Nelson in 1990 it's treated as intuitively obvious. If you'd like to see the statement in print, see e.g. slide 10 of http://www.fnal.gov/orgs/utev/talk-slides/B_movie_fermilab.ps" [Broken].


    Yes, AMS can look at extra-galactic antiprotons. But the thing they are really shooting for is to find anti-nuclei. There is no known process in matter galaxies that produce antinuclei, so even one anti-helium or anti-iron nucleus would settle the issue.

    The annihilation rate is not as large as you think. Annihilation is only one of many ways an electron and positron can interact - for example, an electron and positron can scatter off each other without annihilation. This is, in fact, the way that this evades cosmological problems (and the motivation for Sakharov to write his famous paper). What I don't know is whether this is consistent with baryon acoustic oscillations.

    Note that I am not arguing that there are antimatter galaxies: I'm arguing there is a limit at which we are unable to tell.
     
    Last edited by a moderator: May 4, 2017
  18. Oct 8, 2009 #17

    Astronuc

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    Yes - I should have clarified anti-matter in general, but I believe the orginial goal with AMS-01 was to distinguish between cosmic anti-protons as opposed to local anti-protons, and the bonus would be anti-matter nuclei. It flew briefly on the Shuttle - so didn't have a lot of collection time.

    I attended a presentation by Samuel C. C. Ting back in 2005 where he described AMS-02. It was supposed to be installed in ISS, but the last I heard, it's been postponed until 2010 (and that's probably tentative). :grumpy:
     
  19. Oct 8, 2009 #18

    Vanadium 50

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    AMS-01 didn't have the sensitivity to push much past the limit where we already know from other measurements that everything is matter. Flight time is a big reason for this - the shuttle doesn't stay at orbit for more than a couple of days.

    AMS-02 is in big trouble. It's shuttle mission was canceled, and Prof. Ting has been relentlessly lobbying Congress to get them to require NASA to reinstate it. I don't know how successful he has been: the signals seemed mixed when I was paying attention to it. If it manages to fly, though, it will be ~1000x more sensitive than AMS-01. This is about what it takes to definitely settle the issue one way or the other - at least for the visible universe.
     
  20. Oct 9, 2009 #19

    Wallace

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    Vandium, it's got nothing to do with the level of CP violation, it is about spatial homogeneity. The production of matter and anti-matter in the homogeneous primordial soup, followed by annihilation, happens the same everywhere, unless you postulate that the laws of physics vary from place the place. It doesn't matter what the details of the asymmetry is, what matter is that there is any asymmetry (which leaves matter left over) and that whatever matter is left over is at uniform density everywhere.

    We do know that there cannot be anti-matter galaxies because of the evidence from WMAP that the early Universe was almost perfectly homogeneous. What you are saying violates the entire standard model of cosmology.
     
  21. Oct 9, 2009 #20

    Vanadium 50

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    Remember, I am not arguing that there are antimatter galaxies. I am arguing that there is relatively little direct observational evidence against them at large distances. This was, in fact, the motivation of AMS.

    I brought up CP violation to address the suggestion that CKM CP violation was large enough to cause the baryon asymmetry. It's been known for >= 20 years that it's not. One can wiggle out of this in many ways, including distant antimatter galaxies. This isn't my favorite option (I would be interested in seeing if the PMNS matrix could do it, once those parameters are measured) or probably anyone's favorite option.

    I am certainly willing to believe that cosmological observations made since the AMS proposal disfavor or even exclude the possibility of distant antimatter galaxies. I brought up BAO in my last message. I would like to see a more quantitative argument, though. In particular, there is a perception on PF that matter and antimatter immediately annihilate, when in fact this is not true. They can interact, thermalize, and not destroy each other, which will increase homogeneity. That means the argument becomes quantitative. I'd like to see that.
     
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