The nonconservation of parity observed in certain nuclear and atomic experiments. Parity, the proposition that nature cannot tell left from right, is upheld in experiments observing interactions among the strong and electromagnetic forces but not for those involving the weak nuclear force. In other words, for parity to be “conserved,” it would make no difference in our measurements whether we were observing an interaction among particles directly or in a mirror. For the strong and electromagnetic forces this is true but not for the weak force. The weak force, although not weaker than gravity, is the least palpable of the forces in our ordinary experience. It operates only within the nuclei inside atoms and is therefore hard to probe.