According to inflation, all the structure that we see like galaxies, etc. originated from quantum fluctuations which were expanded during inflation. But since quantum fluctuations always create particle-anti particle pairs, doesn't that mean that at least the vast majority of matter formed would have it's corresponding anti matter within our visible universe? If this was the case wouldn't we constantly see lots of cosmic explosions from colliding masses of matter and anti-matter? Can someone please tell me where my understanding of these concepts faltering?
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1$\begingroup$ Possible duplicates: physics.stackexchange.com/q/24042/2451 and links therein. $\endgroup$– Qmechanic ♦Commented Jun 4, 2017 at 7:41
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$\begingroup$ For an alternative to the excellent answers below, see my answer to this question: physics.stackexchange.com/q/187061 $\endgroup$– Lewis MillerCommented Jun 4, 2017 at 13:17
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2 Answers
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The matter-antimatter asymmetry requires the three Sakharov conditions to be satisfied. I'll summarise that link's explanation. Unfortunately, your question isn't completely solved.
The first condition is that some interactions don't conserve baryon number (I.e. baryons minus antibaryons, baryons being three-quark hadrons such as protons and neutrons). How much asymmetry exists is an open question, as it depends on unverified conditions such as supersymmetry and grand unification.
The second condition, CP violation, has been observed since 1964. However, it's still not known how there's enough of it to explain the observed asymmetry. As with the previous condition, the Standard Model doesn't explain all of the effect, but hopefully new physics soon will.
The third condition is out-of-thermal-equilibrium thermal conditions. Early inflation would ensure this.
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$\begingroup$ so has Baryon number violation been observed in man made experiments? $\endgroup$– alexCommented Jun 4, 2017 at 7:20
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$\begingroup$ @alex Not yet (the main example we've sought is proton decay, and if it happens it's clearly rarer than some GUT models predicted), and sadly neither have supersymmetric particles. $\endgroup$– J.G.Commented Jun 4, 2017 at 7:23
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$\begingroup$ so inflation effectively requires supersymmetry to explain the structure in our universe? $\endgroup$– alexCommented Jun 4, 2017 at 7:26
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1$\begingroup$ @alex Supersymmetry is one way to fulfill the Sakharov conditions, but inflation alone causes the density distribution of the universe's structure, albeit not the fact that antimatter is rarer than matter. $\endgroup$– J.G.Commented Jun 4, 2017 at 8:09
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1$\begingroup$ My probability tables in old physics textbooks show the asymmetry in neutral kaon decay. They tell me it's not enough, but if you've got some it's not hard to believe there's more in the high energy regime. $\endgroup$– JoshuaCommented Jun 5, 2017 at 1:40
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Adding to J.G. answer, it should be noted that Baryon number violation is possible within the Standard Model. This has been shown by t'Hooft in the 70's and this involves non-perturbative effects. Necessarily so since the Electroweak Lagrangian has a global B symmetry and therefore this carries to any Feynman diagram. But this does not prevent the dynamic of the model to break B. Actually t'Hooft processes break B+L but not B-L, where L is the lepton number. The issue is then quantitative: do we get enough of B-violation? As J.G. explained, this must happen out of thermal equilibrium, so there is the added difficulty of correctly computing the dynamic. Still very much an open question.