How could an alien be taught to distinguish left from right using the laws of physics? For decades, modern physics had a simple answer: it couldn’t. 

Since our alien has no knowledge of human conventions, it can’t describe how objects are oriented by using the terms left and right. Equipped only with the laws of physics, the alien would not be able to understand the concepts of ‘left’ and ‘right,’ because they are just tools to describe the spatial relationship between objects rather than a fundamental property of matter. 

Let’s show our alien two scenes: a ‘real’ one on the left and its mirror reflection on the right. How can the alien distinguish between these two scenes? Physical phenomena like electricity and gravity can’t be used to distinguish left from right because in a mirror these forces behave the same. The question remains: what experiment can be done that would identify one scene as inherently ‘left-sided’? 

The notion that no such experiment existed was a core tenet of an early twentieth-century faith in subatomic symmetry, also known as parity. An experiment displays parity when it produces the exact same outcome in a real setup, as it does in the mirrored version; an observer cannot distinguish between them. Take for instance, a symmetrical vase: when reflected or turned, it will appear the same to our alien observer. 

Despite being enshrined in decades of research, this theory was shattered in 1957 through the experimentation of Chinese-American particle physicist Chien-Shiung Wu at Columbia University. 

The Wu experiment

Wu designed and executed an experiment that questioned — and then disproved — the infallibility of parity. After freezing a sample of cobalt-60 nuclei so their north and south poles were aligned, she studied the directions of emitted electrons as the nuclei gained or lost energy. 

In the past, electromagnetic processes had been shown to conserve parity. But the release of electrons is a radioactive decay process that was untested at the time. Wu observed that these electrons were typically emitted opposite the nuclei’s magnetic axis. If parity were conserved, both directions should witness roughly equal emission. Yet the left-handed direction opposite the axis was favoured “by a margin of roughly 1 in 10,000” — according to an article published in September 2022 by the Advancing Physics Society. If our alien recreates this experiment, it will see most electrons being emitted towards the left-handed ‘real’ scene, allowing for an accurate identification. 

These results shocked the physics world, the majority of which was anticipating data that would confirm their pro-parity bias. Yet in the words of Wu, who broke the news of parity nonconservation alongside her colleagues on February 15, 1957: “it is the courage to doubt what has long been established and the incessant search for its verification and proof that pushes the wheel of science forward.”

“The biggest mistake in the Nobel Committee’s history”

Although her work proved the mind-boggling fact that an object and its mirror image can be governed by different physical laws, her name isn’t found in the annals of Nobelists or even the pages of introductory physics textbooks. The 1957 Nobel Prize went to Wu’s male theoretician colleagues, Tsung-Dao Lee and Chen-Ning Yang, despite roughly two-thirds of physics Nobels being granted for experimental work such as hers. 

Her exclusion was met with immediate condemnation. Physicists Wolfgang Pauli and Robert Oppenheimer, the latter of whom frequently sought her advice during the Manhattan Project’s feverish efforts to develop the nuclear bomb, were among the leading voices calling for her recognition. Jack Steinberger — a Nobel laureate in particle physics — repeatedly called it the “biggest mistake in the Nobel Committee’s history.” 

The exact circumstances of Wu’s sidelining have been a longstanding topic of debate. Officially, a candidate cannot win a Nobel for work done in that award cycle’s calendar year. Lee and Yang achieved their theoretical results on December 27, 1956; as Wu confirmed her experiments after the new year had passed, she was automatically disqualified from the 1957 prize. 

However, she was nominated — and once again overlooked — 26 times in subsequent years. “Although I did not do research just for the prize,” she wrote in a letter to Steinberger, “it still hurts me a lot that my work was overlooked for certain reasons.” 

Researchers and science writers throughout the decades have speculated that those reasons predominantly included her identity as an Asian woman — which undeniably made it difficult for her to obtain work, especially after the events of Pearl Harbour. Even her renown among colleagues such as Nobel Prize-winning nuclear physicist Ernest Lawrence — who dubbed her the “most talented experimentalist he had ever known” — was not sufficient to break through the centuries of bias that plague science even to this day. 

Having been raised by parents who were simultaneously teachers and women’s rights advocates, Wu remained a staunch advocate of women in STEM, stating, “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.”

As the accolades she should’ve received cannot be bestowed posthumously, I believe the best way to honour Wu’s legacy is to appreciate the fascinating science of parity violation that she dedicated her life to, and which earned her the title “First Lady of Physics.”