There are rather no doubts that there is more matter than antimatter in our Universe, it is usually assumed that it was created during short baryogenesis (violating baryon number conservation) period of Big Bang.

This asymmetry is used as motivation to search for a fundamental difference between matter and anti-mater, e.g. violating CPT. I wanted to ask why it couldn't be explained by symmetric rules? For example:

In presence of baryon it is a bit more likely for "genesis" of baryon than anti-baryon.

In presence of anti-baryon it is a bit more likely for "genesis" of anti-baryon than baryon.

would lead to statistical symmetry breaking: the more (anti)matter there is, the more (anti)matter will be created - initial tiny random imbalance would be statistically amplified, through annihilation leading to final domination of one of them.

Analogously for life using D-sugars instead of L-sugars: during the origins, the more one type of sugars there was in the environment, the easier life of ancestors using this type of sugar - initial random imbalance should be statistically amplified to total domination.

Do we really need some fundamental asymmetry between matter and anti-matter to explain abundance of matter?

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    $\begingroup$ That's interesting. I don't know much cosmology but one obstacle I could imagine is, how do you make sure all parts of the universe end up the same under your model, instead of having patches of matter and antimatter? $\endgroup$ – knzhou Apr 18 '18 at 9:54
  • $\begingroup$ The general assumption is that just after Big Bang, the soup was so hot that it could violate baryon number conservation - finally leading to the observed asymmetry. A positive feedback should be sufficient (?) - that presence of matter (baryons, electrons) makes that it is more likely to create more baryons than anti-baryons. $\endgroup$ – Jarek Duda Apr 18 '18 at 11:04

I will turn my comment into an answer, still a hand waving one.

CP violation is a quantum mechanical phenomenon, so a phase transition you describe could not happen in a system that is dominated by classical thermodynamics. Classical thermodynamics enters the history of the universe when protons and neutrons are formed,


In classical thermodynamics patches would appear.The interactions of gravitational concentration of energies separate matter in space and there is no reason to suppose that the observable universe would be one such patch, i.e. a fine tuning would be needed. There is no observation of antimatter in the universe, checking for decay products of annihilations .

If instead of in the classical thermodynamic stage, a positive feedback exists in the quark gluon soup, when first baryon numbers appear, as it is a quantum mechanical system the transitions might be induced by a particle similar to the inflaton, ( a violon ;) ) which would then be carrying the CP violation term, and the uniformity of the present universe baryon number violation might be explained, the way the uniformity of the cosmic microwave background is explained.

In a nutshell, CP violation is a quantum mechanical observation, and in quantum mechanics interactions are carried by particles, so your "it is more likely" has to do with coupling constants and feynman diagrams.

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A positive feedback is sufficient to ensure that one type dominates locally, but not globally. Two patches that are sufficiently far apart that they don't interact during the time that these baryogenesis reactions are permitted may easily reach different endpoints, so you end up with patches of matter and patches of antimatter.

We've seen no evidence for such patches (primarily, gamma emission from annihilation reactions on patch borders), but of course the patch size could be larger than the observable universe.

A minor problem with your theory is that it doesn't mention leptons. I'm pretty sure that we need the matter / antimatter ratio of leptons to match that of baryons. Although if neutrinos are Marjorana particles then that (probably) becomes a non-issue. While there are practical difficulties in measuring the neutrino / antineutrino ratio, it would be somewhat surprising IMHO if the matter / antimatter ratio of the charged leptons isn't very similar to that of the baryons.

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  • $\begingroup$ The initial imbalance is assumed to be extremely tiny, equilibrated by later annihilation. Indeed positive feedback should also lead to regions with (tiny) domination of matter or antimatter - the question is if they are separated enough not to mix and equilibrate through annihilation in early history of Universe? Lack of mixing assumes perfect radial expansion, but on particle level they should also have random transverse momentums - diffusing and annihilating through such regions. Do you think regions of initial (tiny) antimatter domination should survive such diffusion? $\endgroup$ – Jarek Duda Apr 19 '18 at 6:28

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