I read these questions and answers and it made me curious.

Baryon asymmetry

Why do we believe baryon asymmetry?

Why does matter-antimatter asymmetry only refer to baryon asymmetry?

How does inflation get rid of initial Baryon asymmetry (if any)?

None of these answer my question:

  1. Is Baryon asymmetry over, or is it still going on in the observable universe? How do we know that no new matter is being created by pair creation and baryon asymmetry? Or is the amount of matter in the observable universe constant?

1 Answer 1


Baryon number violation, one of the requirements for baryon asymmetry, only occurs at any significant rate in the Standard Model at high temperatures, much higher than are known to exist in the universe.

We know experimentally that any other processes that violate baryon number must be quite rare and/or occur only in extreme conditions, since we have not yet observed any.

Theoretically, black holes violate baryon number conservation. Black holes don't have a baryon number, and so when a baryon falls into a black hole, its baryon number is lost. If you consider a neutron star collapsing into a black hole and what happens afterwards, its pretty easy to convince yourself that baryon number can't possibly be conserved.

  • $\begingroup$ wow thanks. Do you say that black holes might be creating matter? $\endgroup$ May 2, 2018 at 19:46
  • 2
    $\begingroup$ @ÁrpádSzendrei No, not likely. Black holes are created overwhelmingly from baryonic matter, so if anything, they are destroying matter. And current black holes are far too cold to produce baryons- a solar mass black hole would take more than $10^{10}$ years to emit one proton's worth of energy as Hawking radiation. $\endgroup$
    – Chris
    May 2, 2018 at 20:02

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