May 31, 1912 – Birth of Chien-Shiung Wu, “The First Lady of Physics”

Keep that title in mind: first LADY – it plays a large part in this amazing story.

Chien-Shiung Wu (May 31, 1912 – February 16, 1997) was born in China, leaving home at age 11 to compete for a place in a boarding school with classes for teacher training; she was ranked ninth among around 10,000 applicants.

After graduating at the top of her class in 1929, she studied in a university, first majoring in mathematics but later transferring to physics. She was encouraged to pursue her PhD abroad in the U.S., and eventually settled on the University of California at Berkeley. (She originally intended to study at the University of Michigan but heard that women were not allowed to use the front entrance of the student center – they had to use a side entrance.)

Wu applied for a scholarship at the end of her first year at Berkeley, but there was prejudice against Asian students, and Wu was instead offered a readership with a lower stipend. Nevertheless, Wu carried on with both her education and with research. She did work on beta decay, a subject on which she would become an authority. She also investigated, using the cyclotrons at the UCLA Radiation Laboratory, the production of radioactive isotopes of xenon produced by the nuclear fission of uranium.

Chien-Shiung Wu

Wu completed her Ph.D. in June 1940. In spite of impressive recommendations, she could not secure a position at a university (Asian and female: two strikes against her), so she remained at the Radiation Laboratory as a post-doctoral fellow.

As Scientific American reported:

While many of her colleagues at Berkeley had been recruited for the war effort, Wu was not asked to join, despite her considerable knowledge of atomic physics. Neither was she asked to remain on at Berkeley in a more permanent role. It was an unfortunate reality that Wu encountered discrimination for being female at a time when most of the top American universities still refused to accept women, either as students or professors. During wartime, she also faced significant ethnic racism.”

Wu was however able to join the Manhattan Project’s Substitute Alloy Materials (SAM) Laboratories at Columbia University in March 1944,The role of the SAM Laboratories, headed by Harold Urey, was to support the Manhattan Project’s gaseous diffusion (K-25) program for uranium enrichment.

In September 1944, Wu helped solve a problem encountered at the newly commissioned B Reactor at the Hanford Site. Physicist John Archibald Wheeler suspected that a fission product, xenon-135, was causing difficulties. Physicist Emilio Segrè, who had worked with Wu at Berkeley, remembered Wu’s work on the radioactive isotopes of xenon. When Enrico Fermi told him about the Hanford reactor problem, Segrè said, “Ask Miss Wu.” Wu had an unpublished paper on xenon-135 and handed over a draft to help fix the problem. Her work demonstrated that xenon-135 was indeed the culprit, and the problem was solved.

Physicist Emilio Segrè, an integral member of the Manhattan Project at Los Alamos as head of the group focused on radioactivity

After the end of the war in August 1945, Wu accepted an offer of a position as an associate research professor at Columbia. In 1949, Wu’s husband Luke Yuan, also a physicist, joined the Brookhaven National Laboratory, and the family moved to Long Island. Wu remained at Columbia for the rest of her career. She became an associate professor in 1952, a full professor in 1958, and the Michael I. Pupin Professor of Physics in 1973.

Of all her accomplishments, Wu is best known for conducting the “Wu experiment” in 1956, which contradicted the hypothetical law of conservation of parity. The discovery of parity violation was a major contribution to particle physics and the development of the Standard Model of physics.

Chien-Shiung Wu in 1958 at Columbia University

As Scientific American explains:

Simply put, parity states that nature does not favor right or left. If you watch a girl throw a baseball through a mirror, the laws of physics will be the same both for the girl and for her mirror image.”

But in 1956 renowned theoretical physicist Richard Feynman floated an idea to his colleagues: What if the parity rule were wrong? Fellow theoreticians Tsung Dao Lee of Columbia and Chen Ning Yang of the Advanced Institute for Study in Princeton believed the “law” could in fact be wrong but did not know how to test it.

Lee approached Wu for advice. Wu immediately got to work designing experiments to test the law of right-left symmetry. At last, on January 9, 1957, Wu and her team were successful.

The next day, The New York Times heralded the “shattering of a fundamental concept of nuclear physics” on its front page. As Maia Weinstock writing in Scientific American pointed out:

The parity results were so spectacular that they garnered a Nobel Prize that very same year, but not for Wu. In October 1957, the Nobel Committee announced that Lee and Yang had won the physics prize ‘for their penetrating investigation of the so-called parity laws which has led to important discoveries regarding the elementary particles.’

Wu was bitterly disappointed. It was not the first time theorists would win a Nobel while a key experimentalist who did the crucial work to back them up did not.”

Chien-Shiung Wu, 1963

Wu garnered a number of other honors, however, including the 1975 National Medal of Science and the 1978 Wolf Prize in Physics (the latter is considered the second most prestigious award in the sciences, after the Nobel Prize). But as the author of an article in The New Inquiry observed:

The popular historical narrative of the Manhattan Project presents it as a masculine, western enterprise, fitting the image of the young, white, male soldier on the battlegrounds of the two world wars. Yet the work of Wu, among many others, shows that the narrative was more complicated than that. Women, non-white, and non-Western people made vital contributions to the Manhattan Project and the physics underlying it. They disappeared from the history of the project as it was used to reinforce the image of the US as the leading Western superpower, both politically and scientifically. The forgotten history of Wu is one where state politics meets gender politics to the detriment of our understanding of scientific development.”