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The Little-Recognized Origin Story behind the 2022 Nobel Prize in Physics

The Little-Recognized Origin Story behind the 2022 Nobel Prize in Physics

2023-03-19 13:32:56

In November 1949 Chien-Shiung Wu and her graduate scholar, Irving Shaknov, descended to a laboratory beneath Columbia College’s Pupin Corridor. They wanted antimatter for a brand new experiment, so that they made their very own, utilizing a machine referred to as a cyclotron. The machine’s multiton magnet was so gigantic that, based on college folklore, a decade earlier directors needed to blast a gap in an exterior wall and recruit the soccer group to maneuver the block of iron into the constructing.

The magnetic discipline produced by a cyclotron accelerates particles to dizzying speeds. Within the lab, Wu and Shaknov used it to bombard a sheet of copper with deuterons, producing an unstable isotope, Cu 64, as a supply of positrons—the antimatter. When a positron and an electron collide, they annihilate one another, releasing two photons that fly aside in reverse instructions. A couple of years earlier physicist John Wheeler had predicted that when matter and antimatter met, the ensuing photons can be orthogonally polarized. Wu and Shaknov have been searching for conclusive proof of Wheeler’s so-called pair idea.

They weren’t the primary. An earlier group of experimentalists had a excessive margin of error, so their outcomes weren’t sufficiently dependable. A second group got here again with outcomes that have been too low to match Wheeler’s predictions. However Wu was recognized for her excessive precision and strategic experimental design. The prior 12 months she had proved Enrico Fermi’s idea of beta decay after greater than a decade of makes an attempt by others.

Wu and Shaknov packed the copper isotope right into a tiny capsule, eight millimeters lengthy, and waited for electrons and positrons to collide contained in the equipment. Then they tracked the ensuing annihilation radiation on the farthest edges of their experiment, utilizing two photomultiplier tubes, anthracene crystals and a scintillation counter as a gamma-ray detector.

In the end they captured considerably extra information than their predecessors, and what they noticed was astonishing. Their proof steered that pairs of photons from particle collisions remained polarized at proper angles to one another—constantly—as if in some way related, even at a distance. Their experiment had proved Wheeler’s pair idea, and Wu and Shaknov printed their findings on New 12 months’s Day in 1950 in a one-page letter to the Bodily Evaluation. However it additionally grew to become the primary experiment to doc proof of one thing weirder: that the properties of entangled particles are at all times completely correlated, regardless of how far aside they stray. Entanglement is so unusual that Albert Einstein thought it proved the place quantum physics went flawed.

In 2022 the Nobel Prize Committee honored experimental work on entanglement by three physicists. John Clauser, Alain Side and Anton Zeilinger had every produced more and more convincing proof for the phenomenon by enhancing on their predecessor’s experimental design. They dominated out one different clarification after one other till, lastly, entanglement was the one conclusion left standing. Though Wu’s 1949 experiment had not been designed to rule out competing explanations, historians agree it was the primary to doc entangled photons. But Wu, who died in 1997, was not talked about when the 2022 awards have been introduced. It isn’t the primary time she has been neglected.

Document identified as an immigration file with photo of Chien-Shiung Wu on the lower right.
Wu’s immigration file from 1936. Credit score: Nationwide Archives 

Chien-Shiung Wu was born the identical 12 months because the New Republic of China, in a small city within the Yangtze River basin. Her father, Zhong-Yi Wu, was an mental, a revolutionary and a feminist. To have fun his daughter’s start and the tip of dynastic rule, Zhong-Yi hosted a celebration within the spring of 1912 the place he introduced his daughter’s title and his new plan to open the area’s first elementary college for women. At a time when most names for women steered a fragile perfume or lovely flower, Zhong-Yi’s title for his daughter translated to “robust hero.”

Chien-Shiung grew up within the crosscurrents of Chinese language nationalism and the New Tradition Motion that criticized conventional Confucian values. In 1936, at age 24, having reached the restrict of what China may provide in physics coaching, she boarded the SS Hoover certain for California. Political actions have been calling for “science and democracy,” together with a technology of students who may elevate China’s standing. Wu was off to pursue a Ph.D. in physics. She would examine underneath pioneers comparable to Emile Segrè, Ernest Lawrence and J. Robert Oppenheimer.

On the College of California, Berkeley, Wu grew to become a star scholar. Her dissertation analysis on the fission merchandise of uranium was so subtle and delicate that it was turned over to the navy and embargoed till the tip of World Warfare II. But Wu had bother discovering a job after commencement. For 2 years she trusted mentors for analysis appointments. On the time, not one of the prime 20 analysis universities within the nation had a girl on the physics college.

Gender bias was not Wu’s solely impediment. A 12 months after her arrival within the U.S., the escalation of World Warfare II reduce off communication with China, and discrimination in opposition to Asian immigrants had intensified, particularly on the West Coast. In 1940 Berkeley’s performing comptroller wrote to Wu’s supervisor to warn him that Wu’s employment can be authorised solely on a brief foundation; lower than a 12 months later he wrote once more: “Laws laid down by the Regents” meant “Miss Wu is just not eligible for employment,” and “quick steps must be taken to dismiss this worker out of your employees.” When Oppenheimer left Berkeley in 1942 to guide the Manhattan Venture, he introduced a lot of his college students alongside; Wu, regardless of her acclaim, was not invited.

Ultimately Wu moved East for a instructing place at Smith School. The next 12 months she grew to become the primary lady employed to the Princeton College physics college. Not lengthy after, the Manhattan Venture lastly recruited her, and he or she performed a quiet, conflicted and essential function within the growth of the atomic bomb. But Wu navigated repeated investigations by immigration authorities and threats of deportation for years. When she had left China in 1936, Wu anticipated to be away for less than a short time. In 1945, when the silence between the U.S. and China lifted, China was embroiled in a brutal civil struggle, and relations cautioned in opposition to returning too quickly. By 1949, the 12 months Wu noticed proof of the criterion for entanglement, Mao Zedong had established communism within the Individuals’s Republic of China, and McCarthyism was ramping up within the U.S., making journey house practically unattainable. She by no means noticed her household once more.

Entanglement emerges from probably the most rigorous branches of arithmetic and physics but has poetic enchantment. Abner Shimony, a thinker and physicist, referred to as it “ardour at a distance.” Entanglement affords the wild notion that after sure particles or methods work together, they will now not be described independently of each other. What occurs to 1, regardless of how far it could journey from its entangled companion, immediately impacts the opposite, as many years of proof now exhibits. The traits of entangled particles are correlated, with none obvious communication, and at any distance. What’s extra, every member of the entangled pair appears to lack a whole set of particular properties till the second when one companion is measured. Then, immediately, the entangled pair might be in sync—even when the particles have drifted galaxies aside. It is the final word star-crossed love.

To know entanglement’s full strangeness, it helps to know that when quantum physicists first got down to quantify the place and movement of subatomic particles, the tiny objects couldn’t be pinned down. Typically particles appeared localized and distinct. At different occasions, the particles confirmed a broad and wavelike conduct, with affect spreading out over giant areas of bodily house relative to their pure measurement. Typically early Twentieth-century experimentalists could not ensure the particles have been even tangible objects in any respect.

In 1927 physicist Werner Heisenberg referred to as this downside the “uncertainty precept.” He studied underneath the founding father of quantum mechanics, Niels Bohr, and Bohr had coined the time period “complementarity” to explain the uncanny experimental outcomes that quantum physics produced. For Bohr, a method to consider your entire complicated scenario was to presume that sure pairs of observations comparable to a particle’s “place” and “momentum” have been complementary to 1 one other; complementary traits couldn’t be perceived or measured precisely within the subatomic world on the similar time. Maybe these traits didn’t even exist till the very second of measurement. Issues bought weirder, although, when the arithmetic of quantum mechanics steered that measuring one particle may instantaneously affect the state of one other particle far-off. This appeared particularly odd if the particles had no measurable attributes within the first place till the 2, in some way, telepathically related.

In 1935 Einstein, Boris Podolsky and Nathan Rosen tried to poke holes in quantum mechanics by declaring how counterintuitive it appeared. The well-known Einstein-Podolsky-Rosen paradox (“EPR”) pointed immediately at entanglement. EPR steered that there needed to be a greater clarification for why and the way one particle may impression its entangled companion quicker than the velocity of sunshine. Einstein derisively nicknamed the phenomenon “spooky motion at a distance.” For Einstein and his co-authors, spooky motion proved that quantum idea was nonetheless incomplete.

Graphic shows the concepts of superposition and entanglement using spheres with arrows indicating “spin” and lines indicating quantum connections between distant particles.

Credit score: Federica Fragapane

Like Einstein, physicist David Bohm felt certain there was a wonderfully affordable clarification for entanglement. Maybe we could not see it fairly but, however the clarification may not be so spooky in spite of everything. It may very well be attributed to hidden variables. Physics merely had extra work to do to seek out them. In 1957 Bohm and his graduate scholar Yakir Aharonov wrote about how photon analysis may harness the well-known EPR paradox to disclose these hidden variables. “[T]right here has been executed an experiment which, as we will see, checks basically for this level, however in a extra oblique manner,” Bohm wrote.

That experiment, says Indianara Silva, a professor of bodily sciences and historical past on the State College of Feira de Santana in Brazil, was the 1949 Wu-Shaknov experiment.

Silva is a historian who’s acutely attentive to the lacking tales of ladies in science. When Wu and Shaknov made the primary exact measurement of Wheeler’s pair-theory in 1949, Silva says, they grew to become the primary to doc entanglement between photons, inspiring many years of later analysis in quantum foundations. Silva has recognized a string of publications by different physicists and historians who acknowledge Wu’s 1949 commentary of entangled photons. She begins with Bohm in 1957 and continues by Zeilinger, one of many 2022 Nobel laureates, who wrote in 1999 that “an earlier experiment by Wu and Shaknov (1950) had demonstrated the existence of spatially separated entangled states.”

Bohm had good cause to belief Wu’s findings. He was a number of years junior to Wu after they have been graduate college students at Berkeley. Each had studied underneath Oppenheimer, and each labored in E. O. Lawrence’s prestigious radiation laboratory. Bohm had each cause to know of Wu’s stellar repute. He acknowledged Wu in a footnote in his 1957 article.

Silva traces how Wu’s experimental work—in 1949 and later in 1971—prompted later entanglement experiments. Silva’s findings have been printed in The Oxford Handbook of the Historical past of Quantum Interpretation in 2022. She factors out how Bohm’s article about hidden variables impressed John Bell, who proposed that the variety of quantum coincidences between particles may very well be predicted and counted. In 1964, in an obscure journal referred to as Physics, Physique, Fizika, Bell mentioned Bohm’s 1957 paper (which referenced Wu’s experiment) and launched his personal new idea. A couple of years later at Columbia, a younger Clauser discovered “Bell’s Theorem” within the library. The idea impressed Clauser to design a brand new experiment, one he hoped may show Bell proper, exhibiting hidden variables have been actual.

Curiously, the Wu-Shaknov letter to Bodily Evaluation in 1950 talks about Wheeler’s pair idea, however it’s silent about entanglement. In 2012 physicist F. J. Duarte referred to as Wheeler’s pair idea “the essence of entanglement.” Different physicists, and historians like Silva, clearly noticed the connection, too. So why did Wu not point out quantum entanglement in her 1950 letter?

Chien-Shiung Wu shown in room with industrial scientific equipment.
Wu proven with industrial scientific tools in 1963. Credit score: Science Historical past Pictures/Alamy Inventory Photograph

Wu may need been hesitant to debate proof of entanglement as a result of all through the Nineteen Fifties and Nineteen Sixties, such quantum-foundations work was stigmatized as junk science. Again then, explains David Kaiser, a professor of physics and historical past of science on the Massachusetts Institute of Know-how, the thought of utilizing an experiment to show or disprove theories about quantum physics or to check for native hidden variables was “not even an inkling” for many physicists. Researchers who explored questions on entanglement usually disguised their analysis as a result of backlash may stymie a promising profession. We’re left to wonder if Wu may need executed in order properly.

Silva factors out that Wu got here again to her 1949 experiment greater than 20 years later to refine it additional. By then, Wu was much more professionally safe, and he or she addressed questions on quantum mechanics immediately. She favored conventional quantum-entanglement interpretations, not Bohm’s idea. In 1971, when she designed a brand new model of the 1949 experiment, Wu wrote that it “ought to actually quiet these proponents of the hidden variables.”

When Clauser printed his proposed take a look at of Bell’s theorem in 1969, he took care to differentiate the Wu-Shaknov experiment from his personal. Clauser had needed to show hidden variables have been actual; as a substitute, in 1972, he disproved the existence of hidden variables and demonstrated entanglement with even higher certainty. He had counted coincidences, a lot as Bell steered, however there have been much more coincidences than hidden variables may clarify. Clauser’s work prompted Side and Zeilinger’s later experiments, which closed lingering loopholes and supported entanglement additional. Collectively these experiments led to their 2022 Nobel Prize.

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By the point Bohm’s paper on hidden variables emerged, a lot had modified in Wu’s life. She had married and moved to the East Coast. She had damaged a glass ceiling at Princeton, had a toddler and had turn into a U.S. citizen. She was on the college of Columbia College, although nonetheless not a full professor.

In 1956 Wu’s Columbia colleague T. D. Lee approached her for recommendation about an odd query. He and his analysis companion, Chen Ning Yang, puzzled if a number of the tiniest particles within the universe may violate long-established expectations. In response, Wu pointed Lee to a physique of analysis, and he or she described a handful of attainable experiments to deal with the questions he posed.

Yang and Lee have been removed from the likeliest of candidates to behave on Wu’s ideas. Each have been theorists, not experimentalists like Wu. In an oral historical past with the Simons Basis half a century later, Yang confessed that neither he nor Lee had any honest perception in 1956 that their speculation would maintain up. In reality, physicists had assumed for many years that the alternative can be true: that symmetry can be among the many immutable, constant patterns in lots of constructing blocks of our universe. Mathematical conservation legal guidelines stated that in the event you ran the identical sequence of occasions ahead and backward in time, the occasions would stay symmetrical. Yang and Lee’s speculation, although, steered that the conduct of nuclear particles in beta decay may not look the identical in the event you flipped the occasions in an imaginary mirror. The concept merely didn’t align with standard scientific thought or with frequent sense.

Like her father, Wu was keen to query mainstream pondering. She suspected the difficulty was necessary, and he or she knew find out how to strategy it. So she designed and led an experiment to deal with her colleagues’ concepts. It meant canceling a visit to China that will have been her first go to house since 1936.

To run the experiment she had in thoughts, Wu wanted to scale back the temperature of radioactive cobalt 60 nuclei till the particles virtually stopped transferring. She needed to check whether or not the daughter particles of nuclear decay shot out in a symmetrical sample—as all of mainstream physics believed they’d—or if the radioactive patterns confirmed a choice for “right-handed” or “left-handed” conduct. She enlisted cooperation from the Nationwide Bureau of Requirements (NBS, now the NIST) in Washington, D.C., as a result of, not like many different labs, they’d the know-how and experience to work at temperatures near absolute zero. For months Wu commuted between New York Metropolis and Washington, overseeing graduate scholar work that supported the experiment.

Graphic compares the expected and observed behavior of cobalt 60 nuclei in Wu’s test of the principle of parity for weakly interacting particles.

Credit score: Federica Fragapane

By January 1957, in shut session with Yang and Lee, Wu and her NBS companions made an astonishing discovery. Beta-decay particles have been barely “left-handed,” not symmetrical as all of physics had assumed. As quickly because it was introduced, Yang, Lee and Wu, together with different experimentalists who adopted Wu’s work, discovered themselves on a nationwide convention circuit, their names and pictures splashed throughout the favored press. When the American Bodily Society met on the New York Resort that 12 months, they offered their findings in what the New Yorker referred to as “the biggest corridor … occupied by so immense a crowd that a few of its members did every thing however dangle from the chandeliers.”

That October, Yang and Lee grew to become the primary two Chinese language People in historical past to win the Nobel Prize. Though Nobel guidelines allowed as much as three award recipients annually, Wu was not included. It may hardly be extra apt that the legislation of physics that Wu toppled was referred to as the precept of parity. Like a prism, the 1957 Nobel Prize separated out components of id like bands of sunshine, rendering the impression of gender extra seen. The next 12 months Columbia lastly promoted Wu to the rank of full professor.

In his Nobel lecture that December, Yang advised the committee and visitors how essential Wu’s experiment had been, making a daring assertion that the outcomes have been as a consequence of Wu’s group’s braveness and ability. Lee would later plead with the Nobel Committee to acknowledge Wu’s work. Oppenheimer publicly acknowledged that Wu ought to have shared within the 1957 prize. Segrè referred to as the overthrow of parity “in all probability the most important growth of physics after the struggle.”

Different scientists criticized Wu’s exclusion from the very best recognition of scientific achievement, too. In 1991 Douglas Hofstadter, the writer of Gödel, Escher, Bach, organized scientists to put in writing letters to the Nobel Committee recommending Wu for the physics prize. And in 2018, 1,600 researchers invoked Wu’s title in an open letter to CERN difficult current-day sexism in physics. “[T]listed here are no less than 4 ladies whose work is related for particle physics who’re extensively considered as having deserved the Nobel prize however who didn’t obtain it, in some circumstances despite the fact that their male colleagues did,” the letter says. Wu’s title seems on the prime of that listing.

Chien-Shiung Wu sitting in the front row in auditorium seating with mostly male colleagues.
Wu at a particle physics convention in Israel in 1967 (seated in entrance row). Credit score: American Affiliation of Physics Lecturers (AAPT), courtesy of AIP Emilio Segrè Visual Archives.

After overthrowing parity, Wu grew to become the primary lady to obtain the Comstock Prize from the Nationwide Academy of Sciences; the primary feminine president of the American Bodily Society; the primary physicist to obtain the Wolf Prize; and the primary residing physicist to have an asteroid named in her honor. Her work pushed open doorways to school instructing within the West for ladies and scientists of colour. In China, she is revered. In 2021 the U.S. Postal Service launched a Forever stamp with Wu’s portrait. At present Wu’s parity experiment is known as an early step on the trail to what would turn into the Commonplace Mannequin of particle physics, and it factors towards attainable solutions about why matter exists in our universe in any respect.

Wu’s early entanglement work, nevertheless, remained in obscurity. Typically by inspecting one a part of a system, we start to understand a associated hyperlink, at a distance. The 2022 Nobel Prize celebrated a set of related experiments that came about at nice distance from each other. Although Wu could not have been awarded the prize posthumously, her early analysis is lastly coming to gentle as an important a part of that entangled historical past, thanks largely to historians comparable to Silva. Society might favor a hero narrative or the parable of a lone genius, however a better look reveals that extraordinary science, like entanglement itself, relies upon essentially on connection.

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