Chien-Shiung Wu’s 1956 experiment showed that parity is not conserved in weak nuclear interactions.
Wu tested a prediction made by Tsung-Dao Lee and Chen-Ning Yang, who proposed that the weak force might distinguish left from right. She cooled radioactive cobalt-60 nuclei to very low temperatures and aligned their spins in a magnetic field. The emitted electrons favored one direction, demonstrating parity violation.
The result overturned the assumption that mirror-reflected versions of weak nuclear processes behave identically. Lee and Yang received the 1957 Nobel Prize in Physics for the theoretical proposal, while Wu’s decisive experimental contribution was not included in the award.
Wu was born in China and built her career in the United States. She also worked on the Manhattan Project and became known as the “Queen of Nuclear Research.”