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Big bang vs antimatter

  1. Dec 28, 2014 #1
    Hi
    My question is about absence of equal antimatter in our universe: If charge and energy is conserved, then this means there was matter before big bang that crunched and created more particles. The charge before and after big bang is conserved; just when two protons are accelerated toward each other and the result of their collision is three protons and an antiproton, one proton and an antiproton annihilate to conserve charge,mass, baryon no etc. so hasn't similar thing happened in Big Bang where antimatter was annihilated with some of the matter (again to conserve charge, energy, etc) and some more matter was left over?

    Thanks
     
  2. jcsd
  3. Dec 28, 2014 #2

    mfb

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    Charge and energy are conserved within the evolution of our universe, this does not have to apply to the beginning (independent of how exactly that looked like).
    Overall, the net electric charge in our universe is extremely close to zero as the number of protons and the number of electrons is very similar. You don't need to violate charge conservation to get a matter/antimatter asymmetry.
    The mechanism that produced the observed asymmetry is unknown - the known differences between matter and antimatter are too small to explain the amount of matter we see.
     
  4. Dec 28, 2014 #3

    Doug Huffman

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    The general topic is baryogenesis, the generic term for the hypothetical physical processes that produced an asymmetry (imbalance) between baryons and antibaryons produced in the very early universe. The baryonic matter that remains today, following the baryonic-antibaryonic matter annihilation, makes up the universe.
     
  5. Dec 28, 2014 #4

    Chalnoth

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    Baryogenesis conserves both charge and energy. Basically, there are an equal number of protons and electrons in our universe.

    What isn't conserved during baryogenesis is baryon number, a number which is conserved* under the strong and weak nuclear forces.

    * Well, it isn't conserved perfectly. But the tiny deviations aren't enough to explain the matter/anti-matter asymmetry we observe.
     
  6. Dec 29, 2014 #5

    Chronos

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  7. Dec 29, 2014 #6

    mfb

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  8. Jan 1, 2015 #7

    Garth

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    While discussing this problem it might be opportune to again refer to the Dirac-Milne universe model which solves the problem a different way; i.e. by proposing there is no asymmetry between matter and antimatter.

    My own interest in the theory is yet again there is a claim that the "linear evolution of the scale factor with time which directly solves the age and horizon problems of a matter-dominated universe" produces a concordant model.

    BTW Happy New Year Everyone!!

    Garth
     
  9. Jan 1, 2015 #8

    Chalnoth

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    Doesn't fit the CMB, though.
     
  10. Jan 2, 2015 #9

    Garth

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    That is the question though, might it fit?

    Several authors claim that the linearly expanding model does fit the CMB power- or possibly might be made to, as the standard model has been, fit by appropriate addition of DM and DE.
    Cosmology of the Dirac-Milne Universe - Indico
    And http://[URL [Broken]] A Concordant “Freely Coasting” Cosmology[/URL]
    It also provides an explanation for the low multipole anomaly as described in the 2013 Planck results.
    Angular Correlation of the CMB in the R=ct Universe
    [/PLAIN] [Broken][/PLAIN] [Broken]

    [/PLAIN] [Broken][/PLAIN] [Broken]Obviously a lot more work is required here before a definitive answer can be given, however, given the fact that the model does not need Inflation, can explain the low power anomaly and resolves a possible age problem in the early universe, perhaps the model ought to be re-examined.
    [/PLAIN] [Broken][/PLAIN] [Broken]
    Garth
     
    Last edited by a moderator: May 7, 2017
  11. Jan 3, 2015 #10

    Chalnoth

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    A model with equal amounts matter and anti-matter doesn't fit with the fact that the CMB exists.
     
  12. Jan 3, 2015 #11

    Garth

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    Why?
    I thought the whole point of the model was that if antimatter is supposed to present a negative active gravitational mass then the universe will be composed of separated (mutually repulsive) domains of matter and antimatter. Each domain of hot plasma in the pre-recombination period contributes to the CMB whilst the combined effect of many domains does not gravitationally affect the evolution of the scale factor which therefore assumes the form of the Milne or empty universe.

    I know the theory has problems, which doesn't? But in the present era of 'precision cosmology' where we know precisely what we don't know perhaps more attention ought to be paid to it.

    In answer to the OP question about absence of equal antimatter in our universe my personal favourite borrows from Wheeler and Feyman's idea that a positron is an electron going backwards in time.

    Thus the baryon asymmetry is coupled to the arrow of time; a matter universe expands forward in time from the BB whilst an anti-matter universe expands backwards in time. They might even be the same universe!!;)

    Garth
     
  13. Jan 3, 2015 #12

    mfb

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    I hope AEgIS settles that question soon.
    As 99% of the mass of nucleons comes from QCD and not the mass of valence quarks, those models were never well-motivated anyway.

    We know we had a rough antimatter/matter symmetry early on in the universe, otherwise we would not have so much energy in photons now.
     
  14. Jan 3, 2015 #13

    Vanadium 50

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    It's settled. AEgIS is an experiment in the category of "a direct measurement substantially weaker than indirect constraints". If antimatter fell up, a) you would be able to make a perpetual motion machine (let light fall down, convert it to an e+ e- pair, lift that up, annihilate it, and let the light fall down - lather, rinse, and repeat) and b) because nucleons contain antiquarks, you would see a composition-dependent gravitational interaction, strongly constrained by Eotvos-type experiments.
     
  15. Jan 3, 2015 #14

    Garth

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    When do we expect the first results from AEgIS?
    Good points, that's why I added a wink!

    Garth
     
  16. Jan 3, 2015 #15

    Garth

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    Confirmatory experiments are still welcome - perhaps we still have something to learn!

    Garth
     
  17. Jan 3, 2015 #16

    PeterDonis

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    Do they? Mesons are quark-antiquark pairs, but AFAIK nucleons (as opposed to antinucleons) are composed of three quarks; for example, a proton is two up quarks and a down quark. No antiquarks.
     
  18. Jan 3, 2015 #17

    Chalnoth

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    At the time the CMB was emitted, our universe was uniform to one part in 100,000. A universe with separate domains of non-relativistic matter and anti-matter couldn't ever get anywhere nearly that uniform in density.
     
  19. Jan 3, 2015 #18

    Vanadium 50

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    Yes, they do. They do not contain valence antiquarks, but they contain antiquarks. Valence quarks are simply the difference between the quarks and antiquarks. It is difficult to impose a difference in gravitation between matter and antimatter without it showing up as a difference in attraction between nuclei and electrons, and that in turn manifests as a composition dependent reaction to gravity.

    As far as the CMB, I am not 100% sure that one couldn't get to this level of uniformity even with separate matter and antimatter domains. I remember talking to de Rujula about this maybe 15 years ago. You certainly cannot get this way if there are large gaps between matter domains and antimatter domains (large = larger than the gaps within the matter domain) but it wasn't clear (at least at the time) that you couldn't make this work. Have there been calculations/simulations since then?

    One can always solve this another way - the visible universe is matter, and "over there somewhere" past the horizon is a region of antimatter. I don't think this is excluded, but it is certainly not satisfying.
     
  20. Jan 3, 2015 #19

    PeterDonis

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    Ah, ok. Yes, I was only talking about the valence quarks.
     
  21. Jan 3, 2015 #20

    Garth

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    In agreement with what Vanadium 50 said, from the Introducing the Dirac-Milne universe paper
    I personally do not much like the Dirac-Milne universe except as an answer to the OP question.

    Garth
     
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