This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
For thirty years, physicists had treated parity, the idea that nature cannot tell left from right, as one of the bedrock symmetries of the universe, alongside the conservation of energy and momentum. By 1956, that confidence had run into a genuine puzzle. Two particles, called tau and theta, appeared identical in mass and lifetime but decayed into final states of opposite parity, a contradiction only possible if parity itself could fail.
Tsung-Dao Lee and Chen-Ning Yang took the puzzle seriously in a way few others did. Reviewing the experimental record that summer, they found that parity conservation had actually been tested directly in the strong and electromagnetic interactions, but never in the weak interaction responsible for radioactive beta decay. Their October 1956 paper did not claim parity was violated; it asked, carefully, whether anyone had actually checked, and proposed several experiments that could.
Chien-Shiung Wu, a Columbia University experimentalist already recognized as one of the finest beta-decay physicists in the world, took up the challenge. Working through the end of 1956 with a team from the National Bureau of Standards, she cooled radioactive cobalt-60 to a fraction of a degree above absolute zero inside a magnetic field, aligning the nuclear spins well enough to measure which direction their decay electrons preferred. If parity held, the electrons would fly off equally in both directions. They did not. Far more emerged opposite the direction of nuclear spin than along it, and a confirming experiment on muon decay, completed within weeks, put the result beyond reasonable doubt.
The 1957 Nobel Prize in Physics went to Lee and Yang alone, for the theoretical insight; the committee had no mechanism for including the experimentalist who supplied the proof. Yang came to regard that as a mistake. He later told a Nobel Committee chairman that Wu's cobalt-60 result was Nobel-class work in its own right and that she should have shared the prize. The imbalance is still debated among historians of science, and it has become one of the field's clearest examples of how a theoretical prediction and the experiment that tests it can be inseparable in substance while being treated very differently in credit.