Wu announced results of her cobalt-60 experiment, the first definitive experimental proof that parity is violated in weak nuclear interactions.
In January 1957, Chien-Shiung Wu announced the results of an experiment she had conducted with a team at the National Bureau of Standards, using ultra-cold cobalt-60 atoms aligned in a magnetic field. The experiment demonstrated conclusively that beta particles emitted during radioactive decay were emitted asymmetrically—a direct violation of the previously sacrosanct law of conservation of parity, which held that physical processes should look identical in a mirror-reflected universe.
This result experimentally confirmed the theoretical prediction made in 1956 by physicists Tsung-Dao Lee and Chen-Ning Yang, who had proposed that parity might not be conserved in weak nuclear interactions. Wu's meticulous, technically demanding experiment—which required cooling cobalt-60 to near absolute zero to align nuclear spins—provided the definitive empirical proof their theory required.
The announcement sent shockwaves through the physics community, overturning a fundamental assumption about the symmetry of nature. Later that year, Lee and Yang were awarded the Nobel Prize in Physics for the theoretical prediction, a recognition many physicists and historians have since argued should have included Wu, whose experimental work was indispensable to proving the theory. Her exclusion remains one of the most cited examples of gender bias in the history of the Nobel Prizes.
Wu's experiment is now considered one of the most important physics experiments of the twentieth century, fundamentally reshaping theoretical and experimental particle physics and establishing her reputation as one of the most skilled experimentalists of her generation.