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Wu, Chien-Shiung free

(31 May 1912–16 February 1997)
  • Sara Diaz

Wu, Chien-Shiung (31 May 1912–16 February 1997), nuclear physicist, was born in Liuhe, China, to Wu Zhongyi and Fan Fuhua. Wu Zhongyi participated in the 1911 Chinese Revolution and advocated for women’s equality. He founded a school for girls in Liuhe, where Chien-Shiung received her early education. He also encouraged her to study science. In 1922 Chien-Shiung went to Soochow Girls School in Suzhou for high school. There she followed in her father’s footsteps by studying science and engaging in revolutionary activities. In 1930 she began studying at National Central University in Nanjing and continued her political activism. After she earned her bachelor’s degree in 1934, she was accepted to graduate school in physics at the University of Michigan at Ann Arbor.

In 1936 Chien-Shiung Wu arrived in San Francisco and met Chia-Liu “Luke” Yuan, a Chinese graduate student in physics at the University of California at Berkeley, whom she would later marry. In the weeks before she was to start at Michigan, she explored Berkeley. She became convinced that it was a better place than Michigan to continue her studies because it was more inclusive to women and there were fewer Chinese students, giving her the opportunity to immerse herself in U.S. culture. Enrolling at Berkeley in 1936, Wu was able to work with famous physicists such as Robert Oppenheimer and the future Nobel Prize winners Ernest O. Lawrence (1939) and Emilio Segrè (1959).

World War II presented Wu with many scientific opportunities, but the 1937 Japanese invasion of her homeland isolated her from family. In fact Wu was unable to safely return to China until 1973. After she earned her doctorate in 1940, Wu stayed at Berkeley as a researcher. Enrico Fermi turned to Wu for advice while he was developing the uranium enrichment process that would fuel the atomic bomb. As the war progressed, anti-Asian sentiment grew and Berkeley refused to employ foreigners. In 1942 Wu married Luke Yuan and the couple moved to the East Coast. Wu took a teaching position at Smith College, but women’s colleges generally lacked adequate research facilities. Ernest Lawrence recommended Wu to several research universities, and Wu was offered a research position at Princeton at a time when women were not yet admitted as students. Eventually the increasing urgency of the war overcame anti-Asian and sexist biases, and in 1944 Wu was recruited by Columbia University to work on uranium enrichment and radiation detectors for the Manhattan Project. After the war Wu stayed at Columbia for the rest of her career, receiving a regular faculty appointment in 1952. Her only son was born in 1947, and in 1954 she became a U.S. citizen.

At Columbia, Wu made her greatest contribution as an experimental physicist. In 1956 the theoretical physicists Tsung-Dao Lee and Chen-Ning Yang consulted with Wu as they developed a theoretical explanation for the “Tau-Theta Puzzle.” The puzzle arose when scientists observed that recently discovered subatomic particles with identical properties, called τ and θ mesons, decayed into pions at different rates. This violated the law of parity in weak interactions. Wu directed Lee and Yang to relevant literature and participated in their brainstorming. Lee and Yang proposed that the law of parity, which had been experimentally established for strong and electromagnetic forces, was not, in fact, a law for weak forces. They published a mathematical proof of their theory. But because the assumption that physical systems behave symmetrically was deeply cherished by physicists, their theory was widely dismissed. Wu was also skeptical of Lee and Yang’s proposal, but she quickly designed a test to experimentally establish whether parity is conserved in weak interactions. The experiment used radioactive cobalt-60 and had not been performed before because it required equipment not widely available. Wu commuted between New York City and Washington, D.C., to collaborate with the scientists Ernest Ambler, Raymond Hayward, Ralph Hudson, and Dale Hoppes at the National Bureau of Standards (NBS), where the equipment was available. Work began in June 1956. By 27 December 1956 the experiment indicated that parity is not conserved in weak interactions. In an interview for the book Particular Passions: Talks with Women Who Have Shaped Our Times (1981), Wu explained that “The test was to take radioactive cobalt 60, place it in a magnetic field, supercool it, and watch where its electrons went. . . . [A] majority of tens of thousands of electrons emitted by the cobalt every second were ejected primarily in one direction—the one opposite the direction in which the nucleus of each atom was spinning” (Gilbert and Moore, p. 69).

The results of Wu’s experiment with cobalt confirmed that parity is not conserved in weak interactions and proved Lee and Yang’s theory correct. Wu was a cautious experimentalist and wanted to ensure the results were replicable before going public, but news of her findings quickly spread through the physics community. She shared her preliminary findings with physicists at Columbia on 4 January 1957. Two physicists, Leon Lederman and Richard Garwin, conducted an experiment using another model and confirmed her results. On 15 January 1957 a press conference was held to announce the discovery to the world. The significance of Wu’s experiment was so far-reaching she was featured on the front page of the New York Times. Lee and Yang won a Nobel Prize for their theoretical work on the Tau-Theta Puzzle later that year.

Many scientists and historians have argued that Wu should have been awarded the Nobel Prize along with Lee and Yang and cited gender bias as the reason for her exclusion. Others have argued that the rules established by the Nobel Committee, which limit the award to three people, led to Wu’s exclusion because of her collaboration with NBS scientists. Wu won nearly every other major prize within the physical sciences for her design of the parity experiment, such as a Research Corporation Award (1958), a Comstock Prize (1964), a U.S. National Medal of Science (1975), the Wolf Prize in Physics (1978), and numerous others. In 1973 she was appointed the first Michael I. Pupin Professor of Physics at Columbia, and in 1975 she was elected the first woman president of the American Physical Society. Later in her career Wu conducted research on sickle cell anemia, retiring from the Columbia faculty in 1981. She died in New York City.

Chien-Shiung Wu made significant inroads for women in science. She was often referred to as the “Queen” or “First Lady” of physics, honorifics that she eschewed. Though it is unclear if her exclusion from the Nobel was based on gender bias, Wu did experience discrimination during her career. She spoke out about gender bias and always defended women’s place within the laboratory. As Wu once quipped, “There is only one thing worse than coming home from the laboratory to a sink full of dirty dishes, and that is not going to [the] laboratory at all.”

Bibliography

Wu’s papers are located at the Columbia University Archives and at the Chien-Shiung Wu Memorial Hall, Southeast University, Nanjing, China. For a firsthand account of her life and the famous nonconservation of parity experiment, see Wu’s short oral history in Lynn Gilbert and Gaylen Moore, Particular Passions: Talks with Women Who Have Shaped Our Times (1981). For a short-form biography of Wu, focusing on her experiences as a woman in science, see Sharon Bertsch McGrayne, Nobel Prize Women in Science: Their Lives, Struggles, and Momentous Discoveries, 2d ed. (1998). The final quotation comes from a tribute to Chinese-American Nobel Prize winners in Chinese American Forum, April 1998, which included Wu’s accomplishments. A full-length biography that examines Wu’s childhood in China is Tsai-Chien Chiang, Madame Chien-Shiung Wu: The First Lady of Physics Research, trans. Tang-Fong Wong (2014). An obituary appeared in the New York Times, 18 Feb. 1997.