A curious number that appeared in the above discussion was the few parts in 10⁹ asymmetry initially between matter and antimatter (or equivalently, the ratio 10⁻⁹ of protons to photons in the present universe). What is the origin of such a number—so close…

…universe is referred to as matter-antimatter asymmetry, and its cause remains a major unsolved puzzle for cosmology and particle physics. One possible explanation is that it involves a phenomenon known as CP violation, which gives rise to a small but significant difference in the behaviour of particles called K-mesons and…

…that the observed imbalance or asymmetry in the matter-antimatter ratio may have been produced by the occurrence of CP violation in the first seconds after the big bang—the violent explosion that is thought to have resulted in the formation of the universe.