baryon-antibaryon annihilation

Due to a slight asymmetry in the electroweak force, for every billion baryons that came into existence, one less than one billion anti-baryon partners were created. When the threshold for baryon creation was reached, and their thermal equilibrium was lost, the baryons and anti-baryons quickly annihilated each other producing radiation. However, one billionth of the baryons remained; this remainder is most of the matter in the universe today.

Baryon: particle consisting of three quarks held together. Familiar baryons are protons and neutrons.

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