On the International Day of Women and Girls in Science, Chien-Shiung Wu, a Chinese-born American physicist, will be commemorated with a U.S. Postal Service (USPS) stamp for her significant contributions in nuclear physics during her 40-year career. More specifically, Wu’s experiment on parity violation that had a monumental impact on particle theory and floored physicists at the time, reports Adrian Cho for Science.
Before Wu brought her innovative skills to physics, she pursued graduate studies in physics at the University of California at Berkeley in 1936 under Ernest Orlando Lawrence, a nuclear scientist. Lawrence was awarded the Nobel Prize in 1939 for inventing the cyclotron. After receiving her Ph.D., she became the first woman hired as a faculty member in Princeton University’s physics department, according to the U.S. Embassy in Georgia. She later left Princeton for Columbia University in New York.
In 1956, Tsung-Dao Lee and Chen-Ning Yang, two theorists, wrote a paper proposing that parity may not remain symmetrical in conditions where particles decayed. They recruited Wu to consult on their experimental design, reports Science.
In physics, it was thought that nature did not distinguish left from right, and everything was completely symmetrical. Therefore, it should apply in at a subatomic level as well. This theory is known as parity, reports Jennifer Ouellette for Gizmodo in 2015. For example, if our world had a mirror image, it would be identical.
While this is true in electromagnetic interactions and strong interactions, the 1956 experiment showed that parity conservation was not true when radioactive decay was involved. Decaying particles were not always symmetrical, and left from the right could be distinguished.
Wu and her colleagues discovered parity violation through experiments involving cobalt-60, a radioactive isotope that Wu suggested for use in the experiments, Science reports. Lee and Yang were awarded the Nobel Prize in 1957 for this experiment, also known as the “Wu experiment." Despite the experiment later bearing her name, Wu did not receive the Nobel prize for her contributions to the groundbreaking find.
“It was an incredibly important experiment, and she was an amazing scientist,” says particle physicist Melissa Franklin at Harvard University to Science
Other contributions Wu made to science include aiding the Manhattan project during World War II through experimentation on uranium enrichment and studying molecular changes to hemoglobin related to sickle cell anemia later in her career. Wu received numerous awards and honors throughout her life, including having an asteroid named after her and the National Medal of Science in 1975.
Wu’s postage stamp illustrated in egg tempera paint, features her in a traditional black and white qipao, against a lapis lazuli background, according to the U.S. Postal Service. William Gicker, the director of stamp services at USPS, tells Science that they want to feature more stamps involving scientific figures and hope that this engages the viewer to ask more questions about who they were and the work they contributed to science.