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B Antiparticles and Cosmology

  1. Jun 8, 2018 #1
    There is an assumption in cosmology say that there is another universe Composed of antiparticles?
    I mean that the atom composed of positron rather than an electron, anti-proton rather than a proton and anti-neutron rather than a neutron.
     
  2. jcsd
  3. Jun 8, 2018 #2

    phinds

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    No, there are highly speculative theories regarding that kind of thing but no such assumption.
     
  4. Jun 9, 2018 #3

    mathman

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    The problem that has not been solved is why matter exists? Big bang led to a lot of energy, where photons can split into matter and antimatter pairs. Why is there an excess of matter?
     
  5. Jun 9, 2018 #4

    Grinkle

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    A boring (because I think its untestable) proposal might be that its anthropic.

    The early universe was infinite in extent, there are many post-expansion regions where complete annihilation took place and some regions where either anti-matter or matter (by chance) pre-dominated. We can only exist in one of those areas, and we will name the region where we exist as "matter", not "anti-matter", because we can't completely shed the human pre-disposition to believe we are special.

    Are there models that eliminate such conjecture by showing that large areas of either matter or anti-matter occurring by chance in an infinite universe are not possible?
     
  6. Jun 9, 2018 #5

    mathman

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    It seems highly unlikely, since these particles are created in pairs, so it is hard to see how they could separate on a large scale.
     
  7. Jun 9, 2018 #6
    believe me, I don't know
     
  8. Jun 9, 2018 #7

    PeterDonis

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    According to our best current model, the Big Bang happened at the end of inflation, and the reheating process that took place then put lots of energy into all of the Standard Model particles, not just photons. The current matter in the universe was not created by photons creating matter-antimatter pairs; it is what's left over after all of the particle-antiparticle pairs that could annihilate as the temperature went down, did annihilate. The reason we still have matter in our universe is that, when that annihilation took place, there was an excess of about one part in a billion of particles over antiparticles; so about one matter particle for every billion photons remained after the annihilation was complete.

    The unresolved question is where that one part in a billion excess of matter particles came from: was it put there by the reheating process that took place at the end of inflation? (And if so, why?) Or did it develop because there are high energy processes, not currently included in our Standard Model of particle physics, that favor matter over antimatter instead of being symmetric between them? (And if so, what are those processes and how can we extend our models of particle physics to incorporate them?)
     
  9. Jun 9, 2018 #8

    PeterDonis

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    As stated in my previous post, your underlying assumption here, that the matter in our current universe was created as particle-antiparticle pairs from photons, is not correct.

    We don't know enough about whatever process created the one part in a billion excess of matter in our universe to tell whether it is possible that there are other "universe" regions which had an excess of antimatter over matter instead.
     
  10. Jun 10, 2018 #9
    The propositions put forth in posts #4 and #7 are not borne out by observations of the microwave background radiation.
     
  11. Jun 10, 2018 #10
    The Universe obviously has a baryon asymmetry, but what about the conservation of charge? Is there an equal amount of plus/minus charge in the Universe?
     
  12. Jun 10, 2018 #11

    PeterDonis

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    Please give more details and references; I don't understand what you are referring to here.
     
  13. Jun 10, 2018 #12

    PeterDonis

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    As far as we can tell, yes, the universe (or at least the part that we can observe) is electrically neutral.
     
  14. Jun 10, 2018 #13

    DAH

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    Hi
    If the early universe created one more anti-matter in a billion over matter, then would stars, planets and life still evolve with opposite charges within atoms?
     
  15. Jun 10, 2018 #14

    phinds

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    Exactly. We would just call it matter since as has already been pointed out, the distinction is arbitrary anyway.
     
  16. Jun 10, 2018 #15
    Well, the distinction is arbitrary up to interacting with stars, planets and life of opposite charge; exchanging space probes, trading cards and letters, and handshakes leads to annihilation... :)
     
  17. Jun 10, 2018 #16

    phinds

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    No, we would call whatever world we lived in matter and the other stuff anti-matter, just like we do now. It's just words. The anti-matter would, as you say annihilate with our matter.
     
  18. Jun 11, 2018 #17
    If there were areas where annihilations didn't take place they would show up as anisotropies in the microwave background radiation that just aren't there. Similarly, if there were a vast number of annihilations leaving a small excess of matter particles, the gamma radiation left from the annihilations would show up as a higher radiation excess than observed as the radiation of recombination.
     
  19. Jun 11, 2018 #18

    PeterDonis

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    Do you have references to support these claims? You appear to be saying that our best current model of the universe is wrong. You need to back up such a claim with strong evidence.

    In particular, are you aware that the ratio of photons to baryons has been measured and is about a billion to one? (That is the basis for my statement in post #7 that the excess of matter over antimatter was about one part in a billion.)
     
  20. Jun 11, 2018 #19
    There are slight anisotropies in the CMBR. There has been much publicity about analysis of results from the Wilkinson Microwave Anisotropy Probe (WMAP) and Planck mission that show both expected and unexpected anisotropies in the CMB map. If we would look at the Universe far from our location, we would not see the same concentric cell structure, or a non-homogeneous Universe. There's still much debate regarding this subject, but the CMB map does indeed correlate with plane of the Earth orbiting the Sun. (There's about 250 million light years space between every shell in this picture). If you take a look at the distribution of quasars in the universe there seems to be a "quasar spherical void" roughly one billion lightyears in radius around us. How to interpret these observations? That is not up to me, but they are significant measurements not to be ignored.
     
  21. Jun 11, 2018 #20
    How about "accretion rates onto SMBHs in galaxy centers drastically decreased as galaxy mergers become much rarer"?
     
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