Monday, October 7, 2013

Gender Bias in Science, Part III: Chien-Shiung Wu

Marie Curie in 1911
Marge:   Sweetie, you could go to McGill, the Harvard of Canada
Lisa:   Anything that's the "something" of the "something" isn't really the "anything" of "anything."
--The Simpsons, "MoneyBart," 2010

The opening quote isn't meant to make fun of McGill (it's a very fine school), but rather to illustrate the point that calling something the "something of the something" can be seen as either a complement or an insult, depending on how you look at it.  For example, people often refer to McGill as the "Harvard of Canada" or refer to Duke as the "Harvard of the South."  Oftentimes the use of those phrases has complementary intentions, but when viewed from another angle, comparing the quality of these two institutions to Harvard (as a sort of "gold standard" for institutions) diminishes their individuality, individual strengths, and identities.  

Curie and Henri Poincare in 1911
This also happens a lot with famous women in science in history.  Lise Meitner was referred to by Einstein as the "German Madame Curie."  The woman scientist of today's post, Chien-Shiung Wu, was often referred to as the "Chinese Madame Curie" or simply as "Madame Wu."  These titles have been bestowed upon these women with good intentions; Madame Curie was obviously brilliant, and being compared with her is a complement for anyone, but it diminishes the individual discoveries and legacy of Meitner and Wu to refer to them in relation to Curie (as some sort of "gold standard" of a woman in science).  They were not "ethnic" copies of Madame Curie.  They were individuals who made brilliant scientific contributions in their own rights, yet unlike Curie, they didn't get the Nobel Prize they each deserved.

This is Part III of an ongoing series detailing some of the past and present issues faced by women in science, with a discussion of famous woman scientists who were denied science's highest prize, the Nobel Prize.  Part I focused on the nuclear physicist Lise Meitner, while Part II discussed the astrophysicist Jocelyn Bell Burnell.

Let's now talk another physicist, Chien-Shiung Wu, who has also been referred to as the "First Lady of Physics."

Wu was born in 1912 in Luihe, China.  Fortunately for her, her father was a schoolteacher who was also an important advocate of women's equality and education.  While studying to be a teacher herself, Wu began borrowing and reading some of her roommates' textbooks on math and physics, which sparked an interest in science.  When she graduated from the Chinese-equivalent of high school at age 17 in 1930, she had the highest grades in her class, and was selected to attend an elite Chinese university in Nanjing.

Chien-Shiung Wu at at science competition in 1958

While she was ecstatic about the idea of being able to study at the university, she was also distraught because she wanted to study physics but feared she did not have the qualifications to compete for a spot to study science.  She was formally trained in high school to be an elementary school teacher, and despite a strong interest and ability, her math and physics background was lacking.  Her father, luckily, thought that there was no reason she couldn't go to school for physics if she wanted to.  He felt that she could learn all she needed to learn before she started at the University of Nanjing, so he bought her books on chemistry, math, and physics.  With his encouragement, Wu taught herself enough of these subjects to be allowed to continue her science studies in college.

Wu at Columbia in 1963 with scientists Y.K. Lee and L.W. Mo

Wu graduated from the University of Nanjing in 1934, and two years later she traveled to California, eventually receiving her PhD in physics from Berkeley in 1940.  Her graduate work was conducted with Ernest Lawrence, who invented the cyclotron particle accelerator, for which he won a Nobel Prize in 1939.  This was a difficult period for Wu, as back home the Chinese were fighting with the invading Japanese Army at the start of World War II, and Wu was basically cut off from all communication with her family.  Nonetheless, she focused her efforts on research, excelled at her studies of physics, and became a skilled experimentalist.  She even married another physicist she met at Berkeley, Luke Yuan.  They eventually had a son, Vincent, in 1947, who also became a physicist.

Wu took joint faculty positions at Princeton and Smith College, and began to work on nuclear fission and a type of radioactivity called beta-decay.  Radioactive decay is a way for an unstable atom with too many protons or too many neutrons to lose either a proton or a neutron to become more stable.  Beta decay is a type of radioactive decay in which a beta particle is emitted from the nucleus of the atom.  A beta particle can be either an electron (a negatively charged subatomic particle) or a positron (a positively charged subatomic particle, sometimes called an antielectron, but not to be confused with a proton).  Other types of radioactive decay are alpha-decay, in which a different type of particle is emitted (an alpha particle) or gamma-decay, in which gamma rays (photons of electromagnetic energy) are emitted.  Beta-decay is particularly important to us today in medicine, because beta radiation is sometimes used to target cancer tumors and beta-emitting substances are sometimes used as medical tracers.        

Wu's research on beta-decay took break when, at the height of World War II, the US government recruited Wu to work on the Manhattan Project, the secret code-name for the development of the first atomic bombs.  She moved to Columbia University to work on the project, and she remained at Columbia until she retired in 1981.  While on the Manhattan project, she worked on developing the processes of enriching uranium ore and separating uranium isotopes to provide the fission fuel for the bombs.  She also helped to improve Geiger counters for detecting radiation.
Wu at Columbia in 1963

After the war, Wu continued research on beta-decay and her work increased her experimental renown.  She also most famously collaborated with two other colleagues, Chen Ning Yang and Tsung-Dao Lee, to disprove a physics theory that had previously been widely accepted as a law.  Stop and think about that for a second.  This was a physical theory that had been so widely accepted as to be considered a law of nature.  We think that such laws should be immutable or concrete, but here was a group of researchers who saw a flaw in the law, and, using a combination of theory and experiments, disproved it.  That's a great thing about science and the scientific method.  The facts are the facts.  You keep developing theories to try to explain the facts, but if the theories don't work or don't hold up to testing or scrutiny, they need to be changed or altered to reflect the current state of knowledge or else discarded.  As we learn more and more about the universe, the state of science is constantly changing and constantly improving.  Everything, no matter how entrenched, is fair game for questioning.      

The law that Wu and her colleagues disproved was called the "principle of conservation of parity."  The law of parity basically proposed that the laws of nature are not biased in any particular direction, and Wu performed beta decay experiments showing that parity was not conserved in certain types of subatomic interactions.  While the theories behind these studies were initially developed by Yang and Lee, they were useless without the experimental ability to test the theories, which only Wu could do.  She spent 6 months researching, testing, and refining Yang and Lee's ideas, and the three of them together altered the way physicists view the universe and subatomic interactions.

Wu at Columbia in 1963

The primary experiment that disproved the law of conservation of parity is today called the "Wu Experiment," performed in 1956.  Wu took a sample of radioactive colbalt-60 and aligned the spin of the atoms by passing a uniform magnetic field over them; at the same time, she reduced atomic vibration by cooling them to near absolute zero.  Colbalt-60 undergoes beta decay to form a stable isotope, nickel-60.  In the process, beta particles (as electrons) are emitted.  If parity was conserved in beta decay, the same number of electrons would have been emitted in both the direction of the nuclear spin as well as in the opposite direction.  However, Wu observed that almost all of the electrons were emitted against the direction of the nuclear spin, demonstrating a directionality to the effect.  When the magnetic field was reversed to reverse the spin, the emission of the electrons also reversed.  This was a revolutionary discovery.  Wu demonstrated that parity was not conserved in subatomic interactions like beta-decay.  This experiment was highly publicized by Columbia, and resulted in several newspaper headlines around the country.                       

Unfortunately, in 1957, Wu saw the Nobel Prize in Physics go to Yang and Lee for this discovery.  Wu did not receive a share of the prize, despite an open spot remaining with only two people named (remember that the Nobel Prize can only go to three individuals at once).  Wu's contributions were overlooked, possibly because they thought that she had made less of a contribution as an experimentalist, or possibly because they thought she made less of a contribution because she was a woman.  We'll unfortunately probably never know the exact reason.  However, most physicists at the time were outraged at Wu not also winning the prize.      

Despite this epic snub, she received numerous other awards, including the Wolf Prize in Physics, the Medal of Science (the highest scientific honor given out by the US), and no less than 8 honorary doctorates.  Interestingly, she also became the first living scientist to have an asteroid named after her in 1980.  She continued to research beta decay, but branched out and studied other biophysical subjects like molecular changes in the hemoglobin protein and implications for sickle-cell anemia.  During her later career, she also became a tireless advocate for women in science.  She died in 1997.

Was Wu a victim of the "Matilda Effect" (the tendency to give credit to a female scientist's male peers, as we previously discussed)?  Or, did the Nobel Prize committee legitimately think (regardless of her gender) that she had less to do with the parity discovery than her male peers simply because she was an experimentalist while they did much of the theoretical work?  We may never know for sure. However, in the less progressive times of 1957, it is difficult to imagine that her gender didn't play at least some role in the decision, particularly in light of the frequent habit of Nobel Prize committees omitting women.  The fact that she was denied the Nobel Prize when there was an open space left on the prize is very fishy no matter how you look at it.  Nonetheless, Wu left an amazing scientific legacy and remains an inspirational figure for any woman interested in physics.    

Sources and Further Reading
  • Images are public domain (Acc. 90-105 - Science Service, Records, 1920s-1970s, Smithsonian Institution Archives)
  • L. Lidofsky.  "Chien-Shiung Wu, 29 May 1912. 16 February 1997"  Proceedings of the American Philosophical Society.  2001.  145:115-126. 
  • California State Polytechnic University Pomona NOVA project.  "Dr. Chien-Shiung Wu."  Available here
  • National Women's History Museum.  "Dr. Chien-Shiung Wu."  Available here.
  • National Women's Hall of Fame.  "Chien-Shiung Wu."  Available here.
  • Columbia 250 webpage on Chien Shiung Wu.  Available here.



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