In its heyday in the 1950s and 60s, the K meson was a spectacular source of profound surprises. Its “strange” longevity gave us the first hint of flavor conservation in the strong interactions, and eventually the concept of quarks as the carriers of these hadronic flavors. Its decay into states of opposite parity freed us from rigid adherence to mirror symmetry Then the neutral kaon was seen to oscillate wondrously between states of opposite strangeness, and finally, in 1964, one of its decay modes yielded up the last great surprise. It provided us the only example we have to this day of CP violation. We had known since 1957 that P (parity inversion) was not an inviolate symmetry of nature. Now the last hope for mirror symmetry—invariance under the combined operation of P and C (charge conjugation)—was also dashed.

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