Chien-Shiung Wu
The Experiment That Broke a Law of Physics
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The audiobook traces Wu's journey from her childhood in China through her education at Stanford and Berkeley. It covers her work on the Manhattan Project, her early experiments with beta decay, and her eventual move to the United States. Chapters detail her research into the weak force and conserved vector current, leading up to her groundbreaking parity violation experiment.
This detailed account reveals how Wu's meticulous work shaped modern physics. Her story includes her role in World War II, her academic rise, and her later advocacy for science education. Anyone interested in scientific discovery and the often-overlooked contributions of women in science will find this biography essential reading.
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Chien-Shiung Wu was born in Liuhe, a town in Taicang, Jiangsu province, China, on May 31, 1912. She was the second child of Wu Zhong-Yi and Fan Fu-Hua. In her family, the generation name Chien was used as the first part of each child’s name, followed by the phrase Ying-Shiung-Hao-Jie, meaning "heroes and outstanding figures." That meant she had an older brother named Chien-Ying and a younger brother named Chien-Hao.
Wu's father, Zhong-Yi, supported her love of science by filling their home with books and newspapers, and he was an engineer who also took part in the 1913 Second Revolution while living in Shanghai. After the revolution failed, he moved to Liuhe, where he became a local leader, leading a militia that fought bandits. He also started the Ming De School for girls and served as its principal. Wu’s mother was a teacher who believed in education for both boys and girls.
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Wu attended the Ming De School for her early learning, where she developed into a quiet but curious child. Her family was well-off, yet she preferred staying indoors rather than playing with other kids. Instead, she listened to the new radio for both entertainment and education. She was drawn to poetry and Chinese classics like the Analects, as well as Western books about democracy that her father shared at home. He would read scientific journal passages aloud to her, not children’s tales, helping her learn to read through his lessons.
Wu left her hometown in 1923 at the age of eleven to attend the Suzhou Women's Normal School No. 2, a boarding school fifty miles from home. The school offered both regular high school and teacher training programs, and introduced science subjects that sparked a growing passion in the young Wu. Admission to the teacher training track was more competitive, as it provided free tuition and board and guaranteed employment upon graduation. Though her family could have paid for the regular program, Wu chose the more selective option and ranked ninth among around ten thousand applicants.
In 1929, Wu graduated first in her class and entered National Central University in Nanjing. Under government rules, teacher-training students had to teach for a year before advancing, but this requirement was only formal in Wu’s case. She took a teaching job at a public school in Shanghai, where the principal was the well-known philosopher Hu Shih. Wu had actually studied under Hu earlier at National China College, and she remembered how impressed he'd been when she finished a three-hour test in less than two hours, sitting front row to catch his attention. Later, when Wu was in the United States, Hu would visit her, and she came to see him as a second father.
From 1930 to 1934, Wu studied at National Central University, starting with mathematics before switching to physics. During this time, tensions were high between China and Japan, and student protests were growing. Wu became involved in political activity and was elected by her peers as one of their leaders. Her colleagues thought her academic excellence might shield her from punishment. She took part in demonstrations, including a sit-in at the Presidential Palace in Nanjing, where she and other students met Chiang Kai-shek.
After finishing her degree, Wu spent two years doing advanced work in physics and teaching at Zhejiang University, then joined the Institute of Physics at the Academia Sinica as a researcher under Gu Jing-Wei, a female professor who had earned her PhD from the University of Michigan. Gu encouraged Wu to pursue her own doctorate overseas and became a key influence in her life. Wu was accepted into the University of Michigan with financial help from her uncle, Wu Zhou-Zhi. In August 1936, she traveled to the United States on the SS President Hoover with her friend Dong Ruo-Fen, a chemist from Taicang. Her parents and uncle saw her depart from the Huangpu Bund. Although her family lived through the Second World War, she wouldn't return to visit them until many years later, during trips to China in the 1970s.
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Chien-Shiung Wu and Dong Ruo-Fen arrived in San Francisco, where Wu decided to study for her graduate degree after visiting the University of California, Berkeley. There she met physicist Luke Chia-Liu Yuan, a middle-class grandson of Yuan Shikai, who had briefly ruled as emperor of China. Wu later teased him about this background, since her own father had once opposed Yuan Shikai. Yuan showed her the Radiation Laboratory, where Ernest O. Lawrence was director. Lawrence would go on to win the Nobel Prize for Physics in 1939 for inventing the cyclotron particle accelerator.
Wu was shocked by the sexism she encountered in America, especially when she learned that women weren’t allowed to use the front entrance at Michigan. She decided then to study at Berkeley instead, drawn not only by its more liberal atmosphere but also by its advanced facilities, including the first cyclotron built by Ernest Lawrence. Her plans to study at Michigan fell through, and she enrolled at Berkeley after being accepted by Raymond T. Birge, the head of the physics department, even though the academic year had already started. At Berkeley, she joined classmates like Robert R. Wilson and George Volkoff, and found close friends in postdoctoral student Margaret Lewis and Ursula Schaefer, a history student who stayed in the U.S. rather than return to Nazi Germany.
Wu missed Chinese food and wasn’t happy with the meals at Berkeley, so she often ate at the Tea Garden with friends like Schaeffer. There, she got free meals not on the menu, thanks to her friendship with the owner. At the end of her first year, she applied for a scholarship, but department head Birge showed bias against Asian students. Instead, Wu and Yuan were offered readerships with lower pay. Yuan later won a scholarship at Caltech. Still, Birge respected Wu’s abilities, which helped her enroll even though the academic year had already begun.
Wu made fast progress in her Berkeley studies and research, working closely with Italian physicist Emilio Segrè, whom she became his favorite student. She studied beta decay including xenon important for nuclear weapons, with Segrè calling her talented and popular. Nobel laureate Luis Alvarez said he knew this graduate student named "Gee Gee," who was the most talented and beautiful experimental physicist he had ever met. Segrè compared Wu to Marie Curie, saying she was more worldly, elegant, and witty. Lawrence described Wu as the most talented female experimental physicist he had ever known. When it came time to present her 1940 thesis, it had two parts: bremsstrahlung electromagnetic radiation from charged particles slowing down, and radioactive Xe. She used beta-emitting phosphorus-32, an isotope made easily in the cyclotron that Lawrence and his brother John H. Lawrence were testing for cancer treatment and as a tracer. This marked Wu's first work with beta decay, a subject she would later become an expert on.
Wu’s work on the production of radioactive isotopes of xenon, created through the nuclear fission of uranium using cyclotrons at the Radiation Laboratory, became the second part of her thesis. Her research impressed her committee, which included Ernest Lawrence and J. Robert Oppenheimer, whom Wu fondly referred to as "Oppie." Oppenheimer was so convinced by her expertise in neutron absorption cross sections that he believed Wu understood everything about the topic. This knowledge would later prove essential when she joined the Manhattan Project.
Wu earned her doctorate in June 1940, and was honored with membership in Phi Beta Kappa, the prestigious academic society in the United States. Despite recommendations from Lawrence and Segrè, she was unable to obtain a faculty position at any university. As a result, she continued her work at the Radiation Laboratory, taking on the role of a postdoctoral fellow. Then, with the outbreak of the Second World War, her path took a new turn.
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Chien-Shiung Wu and her husband Yuan were married on May 30, 1942, at the home of Robert Millikan, who was both Yuan’s academic supervisor and the president of Caltech. Neither of their families could attend because of the war in the Pacific. After the wedding, they moved to the East Coast, where Wu became an assistant professor at Smith College in Northampton, Massachusetts. Yuan worked on radar for RCA. Wu found the job unsatisfying since it only involved teaching with no research opportunities. She asked Lawrence for help, and he wrote letters recommending her to several universities. Smith responded by promoting her to associate professor and raising her salary. Eventually, she accepted a position at Princeton University in New Jersey, where she became the first woman ever hired into the physics department’s faculty, teaching navy officers.
In March 1944, Chien-Shiung Wu began work at the Manhattan Project’s Substitute Alloy Materials (SAM) Laboratories, located at Columbia University. She stayed in a dormitory on campus and traveled back to Princeton each weekend. The SAM Laboratories, led by Harold Urey, supported the gaseous diffusion program known as K-25, which was designed to enrich uranium. Wu collaborated with James Rainwater in a team directed by William W. Havens Jr., whose responsibility was developing radiation detector instrumentation.
In September 1944, Chien-Shiung Wu was contacted by Colonel Kenneth Nichols of the Manhattan District Engineer’s office. She had been frustrated by her lack of professorships and offered to help with the project. At first, she was assigned to build instruments that would check radiation effects from the reactor. Later, she was called in for a more important role. The newly built B Reactor at the Hanford Site had begun shutting down and starting up on its own. John Archibald Wheeler and Enrico Fermi suspected a fission product, Xe-135, might be acting as a neutron poison. Then Emilio Segrè recalled Wu’s 1940 PhD thesis on xenon isotopes and told Fermi to "ask Ms. Wu."
After Fermi contacted Wu, Segrè visited her dorm room with Nichols and took the typewritten draft she had prepared for the Physical Review. The suspicions that Fermi and Wheeler had voiced were confirmed: Wu’s work unknowingly showed that Xe-135 was indeed responsible for problems in the B Reactor, as it had an unexpectedly large neutron absorption cross-section. Wu, concerned that her findings might help other nations develop weapons during the war, waited several months before submitting a full study with Segrè in November 1944. That paper was published just months before the atomic bombs were used the following year.
Wu used her work with radioactive uranium to help create the process for producing enriched uranium at the Oak Ridge facility, which was key to making the atomic bombs. She also helped develop new Geiger counters. Later in life, like many scientists involved in the project, she distanced herself from the Manhattan Project because of its destructive power. In 1962, she advised the Taiwanese president Chiang Kai-shek not to build nuclear weapons. Still, she took comfort in knowing her family was safe in China. When asked about her role years later, she said, “Do you think that people are so stupid and self-destructive? No. I have confidence in humankind. I believe we will one day live together peacefully.”
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After the war ended in August 1945, Chien-Shiung Wu joined Columbia University as an associate research professor. She stayed at Columbia for her entire career. In 1952, she was named associate professor, making her the first woman to achieve tenured status in physics at a university.
In November 1949, Wu conducted an experiment based on the conclusions of the Einstein–Podolsky–Rosen thought experiment, which described quantum entanglement as "spooky action at a distance." She was the first to prove the existence of entanglement using photons, observing angular correlation in their behavior. Her findings confirmed calculations made by Maurice Pryce and John Clive Ward regarding the quantum polarizations of two photons moving in opposite directions. Specifically, Wu’s work provided the first major confirmation of quantum mechanics as it applied to the EPR paradox.
In the 1970s, she conducted a key experiment that tested Bell's inequalities, one of the first of its kind. The results confirmed what quantum mechanics had suggested: the theory does indeed violate Bell's inequalities. This work stood as an important step in understanding the strange behavior of particles at the quantum level.
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After WWII, Wu received a letter from her family, but plans to visit China were interrupted by the civil war leading to Mao Zedong's communist takeover. She wouldn't return to China until decades later to meet her surviving uncle and younger brother. Though Wu did not support Mao, she also did not particularly respect deposed president Chiang Kai-shek or his wife Soong Mei-ling, finding Soong class-conscious while Chiang was too complacent with foreign affairs, willing to let Soong handle diplomatic issues. Still, Wu decided to lend support to the Republic of China or Taiwan, as her teacher Hu carried close ties with the old republic. Due to the war, many were displaced, and younger students would leave for the United States, while scholars in America could not return home. She missed China deeply, often going with Luke to buy fabric to make her own qipao, which she wore under her lab coat as a way to remember the country.
In 1947, Wu became a mother to her son Vincent Yuan Wěichéng, who would later follow in his parents' footsteps by becoming a physicist and attending Columbia University. By 1949, as the Chinese Civil War ended, she joined the Brookhaven National Laboratory and moved with her family to Long Island. She regularly traveled to Brookhaven, then returned weekends to Manhattan, where she worked as Columbia's first female physics professor. After the communists took control of China that same year, her father urged her not to return. Because her passport was issued by the Kuomintang, traveling became difficult—Swiss authorities did not recognize it. Her friend Wolfgang Pauli sometimes had to help secure special visas for her to enter the country. Eventually, she decided to stay in the U.S. With support from Columbia's Charles H. Townes, Wu became a U.S. citizen in 1954.
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After World War II, Chien-Shiung Wu continued her work on beta decay, building on Enrico Fermi’s theory from 1934. A different experiment by Luis Walter Alvarez had seemed to challenge that theory, so Wu decided to repeat it and check the results for herself. By 1949, she had fully confirmed Fermi’s ideas, showing exactly how beta decay operates—particularly in the creation of electrons, neutrinos, and positrons. According to Fermi’s model, most of the electrons should emerge from the nucleus at high speed.
After examining earlier experiments, Chien-Shiung Wu suspected that uneven copper(II) sulfate films caused electrons to lose energy. She adjusted an older solenoidal spectrometer, adding detergent to create a thin, even layer. Her work showed previous differences were due to experimental error, not theoretical problems. She proved electrons moved much slower than thought, matching Fermi's predictions. By examining past research materials, Wu demonstrated the issue was methodological, not theoretical. This established her as the leading expert on beta decay, with her findings later shaping modern physics.
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At Columbia, Wu knew the Chinese-born theoretical physicist Tsung-Dao Lee personally. In the mid-1950s, Lee and another Chinese theoretical physicist, Chen Ning Yang, began to question a hypothetical law of elementary particle physics called the "law of conservation of parity." One example highlighting the problem was the puzzle of the theta and tau particles—two apparently differently charged, strange mesons that were so similar they would ordinarily be considered the same particle. But different decay modes resulting in two different parity states were observed, suggesting that Θ+ and τ+ were different particles, if parity is conserved.
Lee and Yang studied existing experimental results and concluded that parity was conserved in electromagnetic and strong interactions. That’s why scientists expected it would also hold true for the weak interaction, even though no one had actually tested it. Their theoretical work suggested otherwise, and they devised a plan for testing parity conservation in the lab. Wu, with her skill in designing experimental hardware and setting up procedures, told Lee she could carry out the experiment.
Wu decided to conduct her experiment using a sample of radioactive cobalt-60, cooling it down to extremely low temperatures with liquid gases. Cobalt-60 decays by emitting beta particles, and Wu had expertise in that area. The cold temperatures were essential to minimize the movement of the cobalt atoms. She also applied a steady magnetic field across the sample to align the spin axes of the atomic nuclei in the same direction. For this work, she needed access to the facilities of the National Bureau of Standards in Maryland, where she traveled with her equipment to carry out the experiments.
Lee and Yang's theoretical work predicted that beta particles from cobalt-60 atoms would be emitted in an asymmetric pattern, which would mean the law of conservation of parity was wrong. Wu’s experiment confirmed this—parity is not conserved in weak nuclear interactions. Her results showed that the Θ+ and τ+ particles are actually the same, now known as the kaon, K+. Colleagues at Columbia quickly replicated her findings in different experiments. When their results appeared in two papers in the same issue of a physics journal, other labs around the world also confirmed the discovery through many different tests.
The discovery of parity violation changed particle physics and helped shape the Standard Model, which depends on ideas about symmetry and when particles break it. Her work showed that weak interactions behave differently from the other forces, a finding that led to broader CP violation. Otto Frisch, who discovered fission, said people at Princeton often called her experiment the most important since the Michelson–Morley experiment that inspired Einstein’s theory of relativity. The AAUW called it the solution to science’s biggest riddle. This breakthrough helped explain why our universe is made of matter rather than antimatter, by showing how matter-antimatter imbalance could develop after the Big Bang.
Lee and Yang received the Nobel Prize for Physics in 1957, a recognition that went against the usual pattern of the prize being given to experimentalists. Their theoretical work laid the groundwork for understanding parity violation, but the experimental proof came from Wu, whose contribution was left out of the Nobel recognition. Yang and Lee later attempted to support Wu’s nomination for a future Nobel Prize and acknowledged her in their speeches. After their deaths, an examination of the Nobel archives revealed that Wu had been nominated 23 times between 1958 and 1974 by 18 different physicists. A 1988 Nobel laureate, Jack Steinberger, referred to the omission as the Nobel committee’s biggest error. It wasn’t until 1978 that Wu received public recognition for her role, when she was awarded the inaugural Wolf Prize.
Wu’s friend Wolfgang Pauli, who had helped discover the Pauli exclusion principle, was certain that parity was true and was deeply shocked by the results. He, like many other physicists, had lost a big bet against the outcome. Later, he wrote to his Princeton colleague John M. Blatt about the discovery: “I don't know whether anyone has written you as yet about the sudden death of parity. Miss Wu has done an experiment with beta-decay of oriented Co nuclei which shows that parity is not conserved in β decay... We are all rather shaken by the death of our well-beloved friend, parity.” Pauli became even more puzzled when he learned that Wu was not awarded the Nobel Prize. He believed he had predicted the result through dream analysis done by Dr. Carl Gustav Jung.
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Chien-Shiung Wu was promoted to full professor in 1958, and went on to become the first Michael I. Pupin Professor of Physics in 1973. Her students often called her the Dragon Lady, a reference to the comic strip character from Terry and the Pirates, because of her strict nature and high expectations. Yet she cared deeply for her students, sharing lunches with them and learning about their lives. Wu worked tirelessly, from early morning until evening, and her compensation stayed low until Robert Serber took over as chairman. Her scientific contributions were significant in physics and extended into biology and medicine, particularly in understanding molecular changes in red blood cells that lead to conditions like sickle cell disease and anemia.
In December 1962, Chien-Shiung Wu experimentally verified a more precise version of Fermi's beta decay model, lending support to the conserved vector current (CVC) hypothesis advanced by Richard Feynman and Murray Gell-Mann. Her results would be published the following year. The work came after Feynman and Gell-Mann recognized they needed someone with deep expertise in experimental physics to test their idea. Gell-Mann approached Wu directly, asking, "How long did Yang and Lee pursue you to follow upon their work?" Their theory was deeply influenced by Wu's earlier finding that parity is not conserved in weak interactions, which cast doubt on other long-held assumptions, including charge conjugation conservation. For decades, physicists had assumed these principles applied universally—across electromagnetism, gravity, and the strong force—but Wu's findings questioned that. Her contribution was essential to later developments in understanding the electroweak force.
Wu worked with student assistants including Y.K. Lee, Mo Wei, and Lee Rong-Gen from Korea, using equipment at Columbia University's Van de Graaff accelerator, where they used proton, heavy hydrogen, and helium beams. The beta decay sources B-12 and N-12 were produced in the magnetometer, with measurements taken fifty feet away in the magnetometer spectroscopy. Since the labs were locked at midnight, Mo made duplicate keys so everyone could sneak in and out during the early hours. Mo also escorted Wu to her Manhattan apartment. Wu presented her findings at the Hilton hotel on January 26, 1963. She was pleased with the result, saying it gave a complete foundation for Fermi's theory of beta decay and supported the two-component neutrino theory her earlier parity experiment had established. Feynman was very happy with the announcement and called the CVC theory, together with his own contributions in quantum electrodynamics, one of his finest scientific accomplishments.
In the 1960s, Wu continued her investigations into beta decay, focusing on double beta decay. She traveled to a salt mine 2,000 feet beneath Lake Erie in Ohio, where she studied muonic atoms—systems in which muons replace electrons. These experiments were central to understanding the weak force and its role in particle interactions. Her precise work contributed significantly to the development of the conserved vector current theory, offering deeper insight into how certain radioactive decays occur. Through careful observation and methodical analysis, Wu helped clarify the behavior of the weak nuclear force, advancing fundamental knowledge in physics.
Wu later collaborated with Steven Moszkowski to write a textbook called Beta Decay, which was published in 1966. It was the first thorough study of beta decay and became the standard reference on the topic almost immediately. The book remained a key resource well into the twenty-first century.
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After losing her brother in 1958, her father in 1959, and her mother in 1962, Chien-Shiung Wu could not visit mainland China for their funerals because of U.S. travel restrictions. She met her uncle Wu Zhou-Zhi and younger brother Wu Chien-Hao in Hong Kong in 1965. Following President Nixon’s 1972 trip to China, relations improved, and Wu visited again in 1973. She had nearly gone in 1956 but chose to stay in the U.S. to complete her famous experiment while her husband went to China. By that time, her uncle and brother had died during the Cultural Revolution, and her parents’ tombs had been destroyed. Zhou Enlai personally apologized for the destruction. Wu returned to mainland China and Taiwan several times after that.
In the late twentieth century, Chien-Shiung Wu remained one of the world’s leading experimental physicists, widely respected for her work and sought out for advice on testing scientific theories. Herwig Schopper, who led CERN, said that physicists trusted her experiments implicitly, believing “if the experiment was done by Wu, it must be correct.” She carried out research in Mössbauer spectroscopy, applying it to studies of sickle cell anemia, exploring how molecular changes in hemoglobin lead to the disease. Wu also studied magnetism during the 1960s and later worked on Bell’s theorem, which supported the standard interpretation of quantum mechanics.
In later life, Chien-Shiung Wu spoke out more openly on social issues. She protested the imprisonment in Taiwan of the in-laws of physicist Kerson Huang in 1959 and of journalist Lei Chen in 1960. With help from her teacher Hu Shih, Huang’s relatives were released on bail. Lei’s sentence was reduced by President Chiang Kai-shek. In 1964, she addressed gender discrimination at a symposium at MIT. “I wonder,” she asked her audience, “whether the tiny atoms and nuclei, or the mathematical symbols, or the DNA molecules have any preference for either masculine or feminine treatment,” which garnered heavy applause. When people referred to her as Professor Yuan, she corrected them and said she was Professor Wu.
In 1975, while serving as physics department chairman, Serber found that Wu was being paid much less than her male colleagues, despite her lack of complaint or concern about the pay disparity. He took action to adjust her salary so it matched that of her male counterparts, even though Wu herself had never brought it up and remained focused only on her research at Columbia. Wu later joked about the situation, saying, "I was more interested in the science than in the money."
In China, there are many women in physics, and Wu challenged the American misconception that women scientists are all dowdy spinsters—something she blamed on men. In Chinese society, women were valued for who they were, and men supported their accomplishments while they remained eternally feminine. Wu’s advocacies prioritized advancing science. She met with President Gerald Ford in 1975 to formally request that he create an advisory scientific body for the presidency. Ford granted her request, and the Office of Science and Technology Policy was established by law.
After her groundbreaking work in physics, Chien-Shiung Wu remained active in advocating for human rights. In 1989, she protested the Chinese government’s crackdown following the Tiananmen Square incident. That same year, she was awarded the first Wolf Prize in Physics, a recognition that included those whose contributions were considered Nobel-worthy but had not yet received the prize. She retired in 1981 and took the title of professor emerita.
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In her final years, Wu divided her time between the People’s Republic of China, Taiwan, and various American states. She was widely recognized for her strong support of equal access to STEM education, advocating for all students regardless of gender or other forms of discrimination. On February 16, 1997, she suffered a stroke in New York City and was taken to St. Luke’s–Roosevelt Hospital Center, where she passed away. Her granddaughter, Jada Wu Hanjie, reflected on her legacy, saying, "I was young when I saw my grandmother, but her modesty, rigorousness and beauty were rooted in my mind. My grandmother had emphasized much enthusiasm for national scientific development and education, which I really admire."
During her retirement, Columbia held a celebration to honor Wu as the "First Lady of Physics," which brought widespread attention and included a banquet at the Qian Jia Fu restaurant on Broadway. The Polish-American physicist Isidor Rabi remarked that Wu had made greater contributions to science than Marie Curie, despite her nickname as the "Chinese Madame Curie." Maurice Goldhaber once joked that scientists avoided beta decay experiments because they knew Wu would outperform everyone else. When asked who the greatest female physicists were, different scientists listed names like Wu, Lise Meitner, and Curie in varying orders based on their standards. Leon Lederman said both Curie and Wu stood above Meitner, while Valentine Telegdi placed Wu at the top of all female physicists. Regardless of differing opinions, Wu remained highly respected throughout the scientific community.
After her death, Chen-Shiung Wu’s remains were placed in the courtyard of the Ming De School, the institution her father had started and where she herself had studied as a child.
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