This phenomenon was observed for the first time among particles called kaons—states consisting of a strange quark and a down antiquark bound together. It was previously known that the weak force could transform a kaon into an antikaon, and vice versa. The new fact that these experiments revealed was that these processes do not happen with the same likelihood in both directions. There is, in fact, a bias between matter and antimatter built into nature’s very structure. The violation of CP symmetry is exactly what is needed to satisfy Sakharov’s second condition, and this makes it is possible—at
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