Symmetry Breaking

In physics, symmetry means that the rules governing a system remain unchanged after a certain transformation. Symmetry breaking, then, means that the rules may still be symmetric, but a particular state chooses one direction, disrupting the original balance. The most common analogy is a pencil standing upright at the center of a table: before it falls, every direction is equivalent; once it falls, however, it can point in only one direction. CERN uses this example to explain spontaneous symmetry breaking and the Higgs field. The play borrows precisely this structure: near a critical point, the times apply slight or immense perturbations to each person, and a life shifts from “it might have been this way” to “it could only be this way.”

“Symmetry.” In everyday life, symmetry often suggests beauty, balance, or similarity between left and right; in physics, its meaning is more rigorous: after a certain transformation, the laws of physics remain unchanged. Rotate a ball through a full circle and it is still the same ball; move an entire laboratory somewhere else, and as long as the conditions are the same, the laws of physics should not change. This quality of “remaining unchanged after a transformation” is the central intuition behind symmetry in physics.

“Breaking.” Suppose there are many originally equivalent possibilities, and the actual system ultimately chooses one of them. Imagine a pen balanced tip-down on a tabletop. In theory, it is equally able to fall east, west, south, or north; before it falls, no direction across the table has any privilege. But once it falls, it must choose a single direction. The laws of nature show no preference, yet the actual outcome acquires a direction. This is the spirit of spontaneous symmetry breaking.

A round-table meal offers another analogy. Every seat around a round table is initially equivalent; as soon as the first person sits down, positions to the right and left, nearer and farther away, become defined. The table is still round and the rules remain symmetric, but the concrete arrangement is no longer symmetric. Physical systems often behave this way as well: at high temperature or high energy, they appear highly symmetric; after cooling, condensation, or a phase transition, the system chooses a particular arrangement, and a new structure emerges.

Physics also distinguishes two kinds of breaking. The first is “breaking caused by an obvious external force”: if the tabletop is already tilted, for example, the pen naturally falls toward the lower side; this is an external bias. The second is “spontaneous breaking”: the rules themselves do not specify a direction in advance, but once the system settles into a particular state, it must take a side. I suspect drama is most concerned with the second kind: no one tells the audience the ending at the beginning, yet at a certain critical point, small choices, chance events, or institutional pressure push a life toward an irreversible fork.

Symmetry breaking plays an enormous role in physics. It helps us understand phase transitions—for example, when water freezes, water molecules move from a comparatively disordered state into a crystal with orientations and lattice sites. It also lies at the heart of particle physics. The Brout–Englert–Higgs mechanism is related to spontaneous symmetry breaking; the Higgs field gives mass to the W and Z bosons of the weak interaction and is an important part of the Standard Model’s account of the origin of particle mass.

“How the same set of rules can produce different worlds.” Often, life does not lack rules; rather, the rules are too large and the possibilities too numerous. Once historical pressure appears, one path of fate is selected and the other possibilities close.

“Parity” can first be understood as mirror symmetry. Imagine viewing a physical process in a mirror. If the mirrored version follows the same rules as the real one, parity is said to be conserved. Before the 1950s, many physicists believed that nature ought to be symmetric under left-right reflection; at least in the strong and electromagnetic interactions, this belief felt quite natural.

Around 1956, Tsung-Dao Lee and Chen-Ning Yang re-examined this belief and proposed that parity conservation in the weak interaction might never actually have been proven. The crucial point was that a theoretical doubt required an experimental verdict. Chien-Shiung Wu was a leading experimentalist in beta decay, so she designed and advanced a low-temperature experiment centered on cobalt-60. In broad terms, the experiment aligned cobalt-60 nuclei at extremely low temperature in a magnetic field, then observed the directions in which they emitted electrons. If mirror symmetry held, two left-right-reversed arrangements should have produced symmetric results. The experiment instead observed a clear asymmetry, showing that the weak interaction does indeed violate parity conservation.

The result stunned physics because it told humanity that nature can distinguish left from right at the most fundamental level. Official Nobel Prize materials show that the 1957 Nobel Prize in Physics was awarded to Tsung-Dao Lee and Chen-Ning Yang for their penetrating investigation of the so-called parity laws, which led to important discoveries regarding elementary particles. Chien-Shiung Wu’s experimental contribution, however, was not included on equal terms in that Nobel Prize. This is the asymmetry in the distribution of credit that histories of science and of women in science have repeatedly discussed ever since.

The timing of Nobel nominations, the division between theoretical and experimental contributions, the physics community’s preference at the time for theoretical breakthroughs, and biases tied to gender and ethnicity may all have led to such a situation. What can be said with certainty is that without Chien-Shiung Wu’s precise and rapid experiment, parity nonconservation would not have become a physical fact in such a clear form. This is also the sharpest edge of Qu Jianxiong’s story in Symmetry Breaking: she proves an asymmetry in nature’s mirror image while enduring an asymmetry in human institutions.

In physics, breaking is often not an end but a beginning. A perfectly symmetric state can sometimes be too “flat,” without difference or structure; once symmetry breaks, direction, hierarchy, particle mass, material properties, and lattice arrangements can emerge. Without water freezing, there would be no ice crystals; if a magnetic material did not select a direction for its magnetic moments at low temperature, it would show no macroscopic magnetism; if electroweak symmetry did not break, the masses of the W and Z bosons could not be understood in the Standard Model’s way.

Drama, however, can hardly copy the optimism of physics directly. In physics, breaking may generate the structure of the universe; in human history, breaking may also mean destruction, exile, imbalance, and losses that cannot be compensated. Commemorating Ye Qisun after his persecution does not cancel the tragedy; the great honors Chien-Shiung Wu received late in life do not erase her absence from the Nobel Prize or the existence of gender discrimination; Wu Ta-You’s institution-building in Taiwan does not mean that the twentieth-century Chinese intellectual community was never fractured by war and political regimes.

The most important shift in moving from a physical abstraction to drama, then, is this: physical symmetry breaking answers “how structure is generated,” while dramatic symmetry breaking asks “how a person preserves dignity after structures are created or collapse.” The former is natural philosophy; the latter, ethical philosophy.

The historical prototype for the character Ye Qisun (葉啟蓀) is Ye Qisun (葉企孫). Born in Shanghai in 1898, he studied at Tsinghua before traveling to the United States to study physics at the University of Chicago and Harvard University, receiving his Harvard doctorate in 1923. He was a founder of modern physics in China.

Ye Qisun’s most important undertaking was to transform physics from the learning of individuals into an institution within the modern Chinese university. He joined the faculty at Tsinghua around 1925, founded its Department of Physics in 1926, and later served as dean of the College of Science. Tsinghua’s English-language departmental history also states clearly that after the physics department was established in 1926, Ye led it, recruited a number of the era’s important physicists, and trained many people who would later become major figures in physics.

The entrance to his tragedy was the case of his student Xiong Dazhen. During the War of Resistance against Japan, Xiong went to the anti-Japanese base area in central Hebei to work on gunpowder, radio communications, military supplies, and other technical matters; he was later suspected of being a spy during a political purge and was executed. Traditional Chinese materials and Tsinghua sources both mention that Ye used his connections to help raise funds and establish channels for resources. During the Cultural Revolution, the case was brought up again and became an important reason for Ye’s persecution.

In June 1967, Ye Qisun was paraded and denounced by Red Guards and detained. From April 1968 to November 1969, he was arrested and imprisoned by the administrative group of the Central Military Commission; after his release, he remained under isolated investigation until 1975.

Ye Qisun died on January 13, 1977. The irony is that he devoted his life to using education to build a scientific order, only to be destroyed in old age by political disorder. He trained many scientists whom the state would later commemorate, yet when he most needed institutional protection, he lost it.

Ye Qisun (葉啟蓀) corresponds to a “star”: a star provides light and gravity, giving others their orbits. But in the darkness of history, the source of light itself can also be obscured. His story reminds the audience that an educator’s value should not be recognized only when he is honored posthumously; a society truly respects science only if it can protect him while he is alive.

Wu Ta-You moved among mainland China, the United States, Canada, and Taiwan, living through the War of Resistance, the civil war, the Cold War, and the division across the Taiwan Strait. This displacement made him both an inheritor and a beam of light refracted by history: scholars who had belonged to one Chinese scientific community were later divided among different institutional spaces.

In his later years, Wu Ta-You’s ending was comparatively honored. From 1983 to 1994 he served as president of Academia Sinica, advancing reforms at the academy and the construction of Taiwan’s scientific institutions. He stepped down in 1994; in 1992, after forty-six years away from mainland China, he returned for a visit; and he died in Taipei on March 4, 2000. After his death, the Taipei Times described him as a former president of Academia Sinica and also treated him as an important symbol of physics in the Chinese-speaking world and of Taiwan’s scientific institutions.

Wu Ta-You’s scholarly identity was first of all that of a theoretical physicist and educator. After returning to China, he taught at Peking University. When the universities moved inland during the War of Resistance, he maintained teaching and research in physics at the National Southwestern Associated University. He had an important influence on the academic paths of Chen-Ning Yang, Tsung-Dao Lee, and others.

He brought the thinking of modern theoretical physics, symmetry, group theory, and quantum mechanics to a generation of students living through war.

In the play, Wu Dayou is like a “prism.” A prism does not emit light of its own, but it separates light into directions and colors. Wu Ta-You’s dramatic meaning lies precisely in the fact that he does not always confront the age head-on with his head held high, as a conventional hero would. He is more like a person trying to preserve everyday reason, yet repeatedly pushed into war, research ethics, educational responsibility, and institutional choices.

The historical prototype for the character Qu Jianxiong is Chien-Shiung Wu. Born in Liuhe, Taicang, Jiangsu, in 1912, she is described in a National Academy of Sciences biography as one of the most important physicists of the twentieth century. Her work on beta decay and parity nonconservation provided a clear and decisive experimental test for a new paradigm in subatomic physics.

Chien-Shiung Wu’s early education and family environment were important. Her father, Wu Zhongyi, founded Mingde School and valued women’s education. She later attended National Central University, and after going to the United States entered the University of California, Berkeley, eventually becoming a leading experimentalist in nuclear physics and beta decay. During the Second World War, she took part at Columbia University in work related to the Manhattan Project, including experimental problems involving radiation detection and uranium separation.

Her most important place in the history of science comes from the parity-nonconservation experiment of 1956–57. She designed and advanced a low-temperature experiment centered on cobalt-60, observing whether beta decay in the weak interaction obeyed mirror symmetry. The results showed a clear asymmetry in the direction of electron emission relative to nuclear spin: parity is not conserved in the weak interaction. This discovery meant that “left” and “right” were no longer merely human conventions; they became an experimentally definable distinction in nature’s weak interaction.

The 1957 Nobel Prize in Physics, however, was awarded to Tsung-Dao Lee and Chen-Ning Yang, and Chien-Shiung Wu was not included. The U.S. National Park Service states directly that her crucial contribution to particle physics was overlooked in that Nobel Prize. This became a typical case in later discussions of women scientists, Asian immigrant scientists, and the recognition of experimental contributions.

Chien-Shiung Wu later received many major honors, served as president of the American Physical Society, received the National Medal of Science and the Wolf Prize in Physics, among other awards, and retired from Columbia University in 1981. Yet “great honor” is not the same as “symmetrical recognition at the most crucial moment.” Her life presents a sharp paradox: in natural science, she broke humanity’s faith in mirror symmetry; in social institutions, she became a witness to asymmetric recognition.

Another break in her later life was the severing of homeland and family. The U.S. National Park Service notes that she hoped to return home after the war, but the civil war and Cold War blocked the journey. She did not return to China until 1973, by which time her parents had died, their graves had been damaged, and her family had been affected by political movements. Late in life, she continued to speak out on gender equality and political oppression.

Chien-Shiung Wu died of a stroke in New York on February 16, 1997, and her ashes were buried at Mingde School.

Ye Qisun’s model is “rational order broken by political violence.” He represents the long institutional project in which scientific education places its faith: founding departments, hiring teachers, training students, preserving instruments, and transferring the flame of scholarship. During a political movement, however, institutions failed to protect the builder and instead interpreted an educator’s relationships with his students as evidence of guilt. This is the darkest breaking because it was not an accident of nature but a waste produced by human institutions.

Wu Ta-You’s model is “an academic community broken by geopolitics.” He was not destroyed in old age and instead retained dignity and an institutional position in Taiwan and abroad. Yet his path shows how a community of knowledge can be severed by war, civil war, the Cold War, and national borders. What might have been a continuous academic inheritance was forced to become a refraction across regions, regimes, and identities.

Chien-Shiung Wu’s model is “equality before truth broken by institutions of honor.” Her experiment showed that nature’s left and right are not symmetric. But in the human world, asymmetries also exist between theorists and experimentalists, men and women, mainstream identities and immigrant identities. It is not that she received no recognition; rather, the single most crucial recognition did not arrive symmetrically.

When the world no longer operates according to the fairness, order, and reason we expect, can a person still hold fast to truth-seeking, education, and dignity?

In physics, symmetry breaking may generate structure; in history, breaking may also generate injustice. The human responsibility is not to celebrate breaking itself, but to ask after it: Which losses could have been avoided? Which institutions should be corrected? Which people should not be commemorated only after death?

The true power of Symmetry Breaking, therefore, lies in bringing a physical concept back into the human world: when fate is no longer symmetric, when the world is no longer fair, can people still refuse self-deception, refuse servility, and refuse to abandon the search for truth? This is also the spiritual question left to us by the three scientists.