She proved the universe can tell left from right. The Nobel went to the men who guessed.
In 1957, two physicists won the Nobel Prize for an idea. The woman who proved they were right was not on the list.
Her name was Chien-Shiung Wu.
She had come a long way to be overlooked. Born in China in 1912 and raised by a father who ran a school for girls, she sailed to the United States in 1936 to study physics and could not get home before the war closed the door. She worked on the Manhattan Project, solving a problem in uranium enrichment that had stalled the men around her. By the 1950s she was at Columbia, and she was the experimentalist other physicists came to when a measurement had to be exactly right.
For decades, physics rested on an assumption. Nature cannot tell left from right. Watch any process, then watch its mirror image, and the same laws hold in both. It was called the conservation of parity. It was believed so completely that almost no one thought to test it.
Two theorists did. Tsung-Dao Lee and Chen Ning Yang proposed in 1956 that parity might fail for the weak nuclear force, the force behind certain kinds of radioactive decay. It was a startling idea. It was only an idea. Proving it would take an experiment so difficult that many physicists thought it a waste of effort. The men who proposed it needed the best experimentalist alive to try.
They went to Wu.
She put off a long-planned trip to run it. She cooled a sample of radioactive cobalt-60 to a fraction of a degree above absolute zero. She used a magnetic field to line up the nuclei so they all pointed the same way. Then she measured the direction of the electrons the atoms threw off as they decayed. If parity held, the electrons would come out evenly in both directions. They did not. They streamed out one way.
The universe could tell left from right after all. One of the most trusted assumptions in physics was wrong, and Wu was the one who had shown it.
The result shook the field. Physicists who had been certain of parity watched a law of nature overturned by a single, meticulous experiment. It was announced in early 1957. Later that year, the Nobel Prize in Physics was awarded for the discovery that parity is not conserved.
It went to Lee and Yang. Wu, who had turned their guess into a fact, was left off the citation.
She kept working at the front of physics for another three decades. She wrote the standard book on beta decay. She became the first woman to lead the American Physical Society. Colleagues called her the First Lady of Physics, and in 1978 she received the first Wolf Prize in Physics, an honor created in part for the people the Nobel had passed over. The Nobel itself never came.
There is a clean line in this story, and it is worth saying plainly. The theory was the guess. The experiment was the proof. The prize went to the guess.
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