Chien-Shiung Wu: Gender Equality in Physics

Stephanie Pham
April 30, 2018

Submitted as coursework for PH241, Stanford University, Winter 2018

Her Beginnings

Fig. 1: This is a photo of Wu from 1963. By then, she was already a well-respected physicist in the field, working at Columbia University. (Source: Wikimedia Commons)

Dr. Chien-Shiung Wu was a Chinese-American nuclear physicist who is also known as the First Lady of Physics, Chinese Marie Curie, and Madame Wu. Born in 1912 in the Jiangsu province in eastern China, Wu was raised in a family that valued education and gender equality in schools. [1] At only 11 years old, she was sent away from home to a boarding school where she then went to receive her bachelors degree at the National Central University in Nanjing. After, she moved on to Zhejiang University in Hangzhou. Then, at only 24, she left home to sail to America for her postgraduate work in physics. In 1940, she got her PhD in physics at the University of California Berkeley. [2]

Just entering the world of academia after the Pearl Harbor attacks, Wu had to deal with sexism and racism as an Asian woman. [1] Chinese had also been discriminated against for years in American history, with the Exclusion Act in 1882. This made it difficult for her to find an academic position, but she continued pursuing her work.

After moving to the East coast, she taught at both Smith College and Princeton University. [1] Throughout World War II, Wu worked on the Manhattan Project, developing the process of uranium enrichment for nuclear weapons. [2]

For 37 years, she carried out her research with Columbia University's physics department, where she remained for the rest of her professional career. [3] At Columbia, she was named the Michael I. Pupin Professor Emeritus of Physics. [3] Fig. 1 shows a 1963 photo of Wu, who was already working at Columbia at that time.

Wus Experiment: The Nobel Prize in Physics 1957

Arguably Wu's best-known accomplishment was her 1956 experiment that undermined the once-widely accepted and applied principle of conservation of parity, a law of symmetry in physics. [3] The law states that two physical systems, one of which is a mirror image of the other, must behave in identical fashion. [4] This principle referred to all interactions. [4] However, Dr. Tsung-Dao Lee and Dr. Chen Ning Yang, who eventually worked with Wu in the experiment, thought that the law did not apply to subatomic particles in weak interactions responsible for the emission of beta particles. [4] In 1957, Lee and Yang eventually received the Nobel Prize in Physics for this discovery but Wu was not acknowledged despite playing a key role in conducting the experiment. [3] Though Lee and Yang suggested plans for the experiment, Wu was tasked with figuring out how to conduct it, despite the lack of available technology.

The experiments took place at the National Bureau of Standards, where Wu innovatively used its laboratory for the experiment. It was one of the only laboratories in the United States with the technology to cool things to extremely low temperatures. [4] The experiment placed Co-60, a radioactive isotope, in a strong electromagnetic field, which would line up the cobalt's nuclei onto the same axis. This polarization also required cooling the cobalt to 0.003°K. [4] Wu then observed the particles emitted when the cobalt nucleus decayed. She counted the particles that shot out in the same direction of the spin and the ones that did not. The numbers of particles in each direction should be the same, according to parity conservation. However, Wu discovered that more went in the direction opposite to the spin, thereby disproving the universality of the law. [3]


Though Wu was not included in the Nobel Prize in Physics, she received many other awards for her incredible contributions to nuclear physics. She was the first woman to receive an honorary doctorate from Princeton, named president of the American Physical Society, and awarded the National Academy of Sciences Comstock Prize. [3]

Throughout her career, Wu advocated for women and gender equality, in her field and beyond. [1]

© Stephanie Pham. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] J. Scutts, "The Manhattan Project Physicist Who Fought for Equal Rights for Women," Time, 14 Jun 16.

[2] J. Guo, "Chien-Shiung Wu and Her Contributions to Nuclear Physics ,"Physics 241, Stanford University, Winter 2017.

[3] W. Dicke, "Chien-Shiung Wu, 84, Dies; Top Experimental Physicist," New York Times, 18 Feb 97.

[4] R. Hudson, "The Reversal of Parity Law in Nuclear Physics," in A Century of Excellent in Measurements, Standards, and Technology, ed. by D. R Lide, U.S. National Institute of Standards and Technology, Special Publication 958, January 2001, p. 111.