The Universe today is believed to be charge neutral and since nearly all the Standard Model content is protons, electrons, neutrons, neutrinos and photons; this requires #protons = #electrons. However in the early Universe, the Standard Theory of Cosmology will have neutrino decoupling at about one second and the hadrons freezing out with a mass hadron anti-hadron annihilation following shortly after. For some seconds following this we have the lepton age, electron-positron freeze out and then mass electron-positron annihilation. Given the two mass annihilations happen at different times it seems unnatural that the number of proton anti-proton pairs annihilating is exactly equal to the number of electron-positron pairs annihilating but this seems to be required for charge neutrality. Are there any explanations/clues relating to this coincidence?
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If you assume:
- The initial state of the universe was charge neutral.
- Charge is conserved.
Then, regardless of how you get there, the universe must be charge neutral. If you have an excess of positive particles of some sort, it must be balanced by an excess of negative particles of other sorts.
