Chien-Shiung Wu Tests the Rule

Chien-Shiung Wu was born in China in 1912. She became an experimental physicist and later worked in the United States. Colleagues respected her skill with difficult measurements.

In the 1950s, physicists wondered whether a rule called parity always held. The rule suggested that some events should behave like their mirror images. Two theorists proposed that weak nuclear interactions might break it. They asked Wu to design a test.

Wu's team cooled radioactive cobalt to an extremely low temperature and aligned its nuclei in a magnetic field. The particles emitted by the cobalt did not leave equally in mirrored directions. The result showed that parity was not conserved in this interaction.

The experiment changed physics. The theorists received a Nobel Prize, while Wu did not share it. Her work remains a clear example of how experimental design can decide between ideas. A bold proposal needed an instrument, controlled conditions, and someone able to make nature answer.