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Chien-Shiung Wu
1912–1997 · Experimental Physicist
A leading experimental physicist of the twentieth century, known for the cobalt-60 experiment that proved parity violation in weak interactions.
“I wonder whether the tiny atoms and nuclei, or the mathematical symbols, or the DNA molecules have any preference for either masculine or feminine treatment.”
Why is this scientist famous?
Chien-Shiung Wu was one of the leading experimental physicists of the twentieth century, famous for leading the landmark cobalt-60 beta-decay experiment that provided the first experimental evidence that parity is not conserved in weak nuclear interactions.
Wu's experiments transformed our understanding of the weak interaction and showed that nature does not always treat left and right symmetrically. Her precision work helped shape modern particle physics, while her early photon experiments also connect her legacy to today's science of quantum entanglement. Her career remains a powerful example of how careful experiments can overturn ideas that scientists once considered fundamental.
Chien-Shiung's story
Early Life in China
Chien-Shiung Wu was born on 31 May 1912 in the small town of Liuhe in Jiangsu Province, China, near the mouth of the Yangtze River. Her father, Wu Zhong-Yi, was a remarkable man who founded a girls' school and passionately believed in educating daughters as well as sons. He gave his daughter a name that means 'courageous heroism,' and she grew up in a household where learning was treasured. Young Chien-Shiung excelled at mathematics and science, and her father's encouragement helped her pursue an education at a time when most Chinese girls had none. She went on to study physics at National Central University in Nanjing, where she graduated at the top of her class in 1934.
Journey to America
In 1936, Wu sailed to the United States to pursue graduate studies, leaving behind a homeland descending into war. She enrolled at the University of California, Berkeley, where she studied under Ernest Lawrence, the inventor of the cyclotron, and worked alongside some of the brightest physicists of the era. Berkeley was at the centre of nuclear physics, and Wu thrived in the intense, competitive atmosphere. She earned her doctorate in physics in 1940, with dissertation research that included beta-particle radiation and fission products of uranium. As a woman and as a Chinese immigrant, she faced discrimination at every turn, but her experimental skill was so extraordinary that colleagues sought her out for the most difficult measurements.
The Manhattan Project
During the Second World War, Wu joined the Manhattan Project at Columbia University's SAM Laboratories. She helped develop the gaseous-diffusion process for separating fissile uranium-235 from uranium-238, a critical step in building the atomic bomb. Her work on uranium separation was classified, and for years she could not speak publicly about it. After the war, she remained at Columbia as a research scientist, building a reputation as the world's foremost expert on beta decay, the process by which a neutron transforms into a proton, an electron, and an antineutrino.
The Parity Experiment
In 1956, theoretical physicists Tsung-Dao Lee of Columbia University and Chen-Ning Yang of the Institute for Advanced Study proposed that parity conservation, a long-held principle that the laws of physics should look the same in a mirror, might fail in weak nuclear interactions. They could not test their theory themselves; they needed a world-class experimentalist. Wu designed and led an extraordinarily precise experiment using radioactive cobalt-60 atoms cooled to near absolute zero. The experiment was carried out at the National Bureau of Standards in Washington, D.C., with the collaboration of Ernest Ambler, Raymond W. Hayward, Dale D. Hoppes, and Ralph P. Hudson. The results were announced in January 1957 and published in Physical Review on 15 February 1957: nature does distinguish left from right. Parity is not conserved in weak interactions. Lee and Yang received the 1957 Nobel Prize in Physics for their theoretical work. Wu and the experimental team were not included in the award, a decision many scientists have since considered deeply unfair.
Legacy
Although she was not included in the Nobel Prize, Wu received many major honours for her work in physics. She was awarded the National Medal of Science in 1975 and the Wolf Prize in Physics in 1978, and she became the first woman to serve as president of the American Physical Society. She was also the first woman to receive an honorary doctorate from Princeton University. At Columbia, she was known as 'the Dragon Lady' for her exacting standards and fierce dedication to precision. She never stopped advocating for women in science and for the careful, honest experimental work she believed was the heart of physics. She died on 16 February 1997 in New York City, having changed our understanding of the universe and opened doors for generations of scientists who followed.
What did they discover?
Parity Violation in Weak Interactions
Wu designed and led the cobalt-60 experiment, carried out with Ernest Ambler, Raymond W. Hayward, Dale D. Hoppes, and Ralph P. Hudson at the National Bureau of Standards, that proved weak nuclear interactions do not conserve parity. The theoretical proposal came from Tsung-Dao Lee and Chen-Ning Yang, who received the 1957 Nobel Prize for it. The result overturned a cherished assumption and reshaped particle physics.
Manhattan Project Uranium Separation
During the Second World War, Wu helped develop methods used in the gaseous-diffusion process for separating uranium-235 from uranium-238 at Columbia's SAM Laboratories, contributing to the Manhattan Project.
Beta Decay Research
Wu became the world's leading authority on beta decay, the process by which a neutron transforms into a proton, an electron, and an antineutrino. Her precise measurements helped confirm and refine the theory of weak interactions.
Early Photon Entanglement Experiment
In 1949, Wu and her graduate student Irving Shaknov carried out a precision experiment studying pairs of photons produced by electron-positron annihilation. Their work is now recognised as an early experimental demonstration of the correlated behaviour associated with quantum entanglement.
Amazing facts
Her father named her Chien-Shiung, meaning 'courageous heroism,' and she lived up to the name throughout her life.
She was the first woman to receive an honorary doctorate from Princeton University.
The theoretical proposal that parity might not be conserved came from Lee and Yang; Wu designed and led the experiment that proved it, but only Lee and Yang received the Nobel Prize.
The parity experiment was carried out at the National Bureau of Standards with a team of four NBS physicists: Ernest Ambler, Raymond W. Hayward, Dale D. Hoppes, and Ralph P. Hudson.
She was nicknamed 'the Dragon Lady' by her students for her fierce dedication to experimental precision.
She was the first woman to serve as president of the American Physical Society.
She received the Wolf Prize in Physics in 1978, one of the most prestigious awards in the field after the Nobel.
Her birth date is sometimes listed as 29 May 1912 in older records, but authoritative modern biographies use 31 May 1912.
Timeline
Born in Liuhe, Jiangsu Province, China
Graduated at the top of her class in physics from National Central University, Nanjing
Sailed to the United States to begin graduate studies at UC Berkeley
Earned her PhD in physics from UC Berkeley with a dissertation on uranium decay
Joined the Manhattan Project at Columbia University's SAM Laboratories
With Irving Shaknov, carried out an experiment that documented early experimental evidence of photon entanglement
Designed the parity violation experiment and carried it out at the National Bureau of Standards with Ambler, Hayward, Hoppes, and Hudson
Parity experiment results published, proving parity violation in weak interactions; Lee and Yang received the Nobel Prize
Appointed the first Michael I. Pupin Professor of Physics at Columbia University
Became the first woman president of the American Physical Society and received the National Medal of Science
Received the Wolf Prize in Physics
Died in New York City, age 84
Awards & honours
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