This is what the New York Post wrote about Chien-Shiung Wu: “This small, modest woman was powerful enough to do what armies can never accomplish: she helped destroy a law of nature. And laws of nature, by their very definition, should be constant, continuous, immutable, and indestructible.” If you are wondering, Chien-Shiung’s name means “courageous hero,” which, of course, is terribly fitting.
So which law of nature was the New York Post talking about? And who was this brave soul who dared smash such laws?
It has to do with ‘The Law of Conservation of Parity,’ which Wu’s work at Columbia helped to completely upend.
Chien-Shiung Wu was a Chinese-born American experimental physicist. Her honorary nicknames included: the ‘Chinese Marie Curie’, the ‘First Lady of Physics’, ‘Madame Wu’, and the ‘Dragon Lady’ (given to her by her students at Columbia University for her uncompromising standards). Hailed as one of the giants of physics by her colleagues, she had no equal in the field of beta decay; she was known for her brilliant problem-solving skills, high energy, and for the elegance of her experiments.
Chien-Shiung (pronounced Chen Shoong) was born on May 31, 1912, in Liu He, a small town near Shanghai, China. There was no school for girls in Liu He, so her father (an engineer by training) started one. The Ming De School, where her father served as a headmaster and her mother worked as a teacher, was one of the first schools in China to admit girls.
At age nine, Chien-Shiung enrolled at a boarding school in Soochow, where she discovered mathematics, physics, and chemistry. After graduating as valedictorian, Wu joined the prestigious National Central University in Nanjing. Like her role model – Marie Curie, Wu was dedicated to her work. She graduated from the National Central University in 1934 with a B.S. in physics and took a research job at the National Academy of Sciences in Shanghai. Her mentor at the Academy, a female professor Jing-wei Gu, had earned her Ph.D. in the United States and advised Wu to do the same.
Wu sailed to the United States in 1936. She enrolled in graduate school at the University of California at Berkeley, under the supervision of one of the world’s leading physicists, Ernest Lawrence, who had won the Nobel Prize for inventing the atom-smashing machine known as the ‘cyclotrone’. Chien-Shiung received her Ph.D. in physics in 1940.
WATCH: The First Lady of Physics
After graduation, Wu worked as Ernest Lawrence’s research assistant, establishing herself as one of the leading experts on nuclear fission. Her achievements merited a faculty position at Berkeley, but she was a woman (and an Asian), which made it difficult.
In 1942 Chien-Shiung married a fellow physicist from Berkeley, Luke Yuan, and the couple moved to the East Coast. Wu became a professor at Smith College (a women’s college in Northampton, Massachusetts). Luke worked on radar devices with RCA in Princeton, New Jersey. A year later, partly because of a shortage of male professors during the war, Wu got offers to teach at MIT, Princeton, and Columbia University. She took the Princeton offer to teach introductory physics to naval officers. She was the first female instructor in the Physics Department at Princeton.
In 1944, Wu joined Columbia University’s Division of War Research. Her work was part of the ‘Manhattan Project’ to develop an atomic bomb. She helped develop the process for separating uranium metal into U-235 and U-238 isotopes, and improved ‘Geiger counters’ for measuring nuclear radiation levels. After the war, Wu remained at Columbia to continue with her research. She taught at Columbia until her retirement in 1981. The highlight of Wu’s career was disproving what was then considered a ‘law’ of nature and was known as ‘The Law of Conservation of Parity.” Her discovery shattered a fundamental concept of nuclear physics that had been accepted for over 30 years.
According to the parity principle, two physical systems (one of which is a mirror image of the other) must behave in identical fashion. For example, during radioactive decay, atoms act symmetrically by ejecting the same number of particles on the right as on the left, which means that Nature is symmetrical and makes no distinction between left and right, or opposite sides of a subatomic particle.
In 1956, two Chinese-born theoretical physicists, Tsung-Dao Lee of Columbia University and Chen-Ning Yang of Princeton, suggested that although the ‘law’ was valid for electromagnetic and strong nuclear forces, it might not hold for weaker nuclear force (these forces, along with gravity, are known as the ‘Four Fundamental Forces’ of Nature).
The two scientists approached Wu (who had a world-wide reputation for her work on beta decay) to perform an experiment to test their theory. Wu cancelled her planned trip to Europe and the Far East to test the theory that most physicists thought would not stand. Among them were Chien-Shiung herself, who gave the theory one-in-a-million chance of being correct, Richard Feynmann (who lost a fifty dollar bet over the issue), and Wolfgang Pauli, one of the pioneers of quantum physics.
Wu chose to do the experiment by using the salt of radioactive cobalt-60, which decays by beta particle emission. She placed the cobalt in a strong magnetic field to line up the north-south magnetic poles of its nuclei; she supercooled the cobalt to minimize the random thermal motions of the atoms and watched where the emitted electrons went.
She found that the majority of the ejected electrons went in one direction, behaving asymmetrically. This proved that parity did not apply to weak subatomic interactions. The news stunned the scientific world. Lee and Yang went on to receive the Nobel Prize for this groundbreaking discovery. Cien-Shuing Wu was not included in the award. In 1964, Wu went on to experimentally confirm a theory by Richard Feynmann and Murry Gell-Mann regarding the conservation of vector current in nuclear beta decay.
By the time Chien-Shiung Wu retired, she was one of the world’s leading experimental physicists. She was a recipient of multiple prizes and honors. She was the first woman to receive an honorary doctorate from Princeton University; the first female President of the American Physical Society (elected in 1975); and the first living scientist to have an asteroid named after her. Her book ‘Beta Decay’, published in 1965, became a standard text in nuclear physics.
After 1981, Wu traveled and lectured widely, encouraging young women to consider scientific careers. She was a passionate critic of gender barriers and gender discrimination in scientific circles. ‘I sincerely doubt, -she said – that any open-minded person really believes in the notion that women have no intellectual capacity for science and technology.’
Wu’s commitment to her work was legendary. She wrote, ‘There is only one thing worse than coming home from the lab to a sink full of dirty dishes, and that is not going to the lab at all.’
Chien-Shiung Wu died of stroke on February 16, 1997, in New York City.