Particle physics is an obscure subject for most people but everyone sat up and took notice when the Large Hadron Collider discovered the particle named after Peter Higgs in 2012. The Higgs boson propelled his name to the front pages of newspapers that until then hadn’t bothered about the differences between bosons and fermions. On the other hand, it also validated a hypothesis he and his peers had made 50 years ago and helped the LHC’s collaborations revitalise their outreach campaigns.
However, much before the times of giant particle colliders – in the late 1950s, in fact – a cascade of theories was being developed by physicists the world over with much less fanfare, and a lot more of the quiet dignity that advanced theoretical physics is comfortable revelling in. It was a silent revolution, and led in part by the mild-mannered Yoichiro Nambu, who passed away on July 5, 2015.
His work and its derivatives gave rise to the large colliders like the LHC at work today, and which might well have laid the foundations of modern particle physics research. Moreover, many of his and his peers’ accomplishments are not easily discussed the way political movements are nor do they aspire to such privileges, but that didn’t make them any less important than the work of Higgs and others.
Yoichiro Nambu also belonged to a generation that marked a resurgence in Japanese physics research – consider his peers: Yoshio Nishina, Masatoshi Koshiba, Hideki Yukawa, Sin-Itiro Tomonaga, Leo Esaki, Makoto Kobayashi and Toshihide Maskawa, to name a few. A part of the reason was a shift in Japan’s dominant political attitudes after the Second World War. Anyway, the first of Nambu’s biggest contributions to particle physics came in 1960, and it was a triumph of intuition.
There was a span of 46 years between the discovery of superconductivity (by Heike Kamerlingh Onnes in 1911) and the birth of a consistent theoretical explanation for it (by John Bardeen, Leon Cooper and John Schrieffer in 1957) because the phenomenon seemed to defy some of the first principles of the physics used to understand charged particles. Nambu was inspired by the BCS theory to attempt a solution for the hierarchy problem – which asks why gravity, among the four fundamental forces, is 1032 times weaker than the strongest strong-nuclear force.
With the help of British physicist Jeffrey Goldstone, Nambu theorised that whenever a natural symmetry breaks, massless particles called Nambu-Goldstone bosons are born under certain conditions. The early universe, around 13.75 billion years ago when it was extremely small, consisted of a uniform pond of unperturbed energy. Then, the pond was almost instantaneously heated to a temperature of 173 billion Suns, when it broke into smaller packets called particles. The symmetry was (thought to be) spontaneously broken and the event was called the Big Bang.
Then, as the universe started to cool, these packets couldn’t reunify into becoming the pond they once made up, evolving instead into distinct particles. There were perturbations among the particles and the resultant forces were mediated by what came to be called Nambu-Goldstone bosons, named for the physicists who first predicted their existence.
Nambu was able to use the hypothetical interactions between the Nambu-Goldstone bosons and particles to explain how the electromagnetic force and the weak nuclear force (responsible for radioactivity) could be unified into one electroweak force at higher temperatures, as well as how where the masses of protons and neutrons come from. These were (and are) groundbreaking ideas that helped scientists make sense of the intricate gears that turned then to make the universe what it is today.
Then, in 1964, six physicists (Higgs, Francois Englert, Tom Kibble, Gerald Guralnik, C.R. Hagen, Robert Brout) postulated that these bosons interacted with an omnipresent field of energy – called the Higgs field – to give rise to the strong-nuclear, weak-nuclear (a.k.a. weak) and electromagnetic forces, and the Higgs boson. And when this boson was discovered in 2012, it validated the Six’s work from 1964.
However, Nambu’s ideas – as well as those of the Six – also served to highlight how the gravitational force couldn’t be unified with the other three fundamental forces. In the 1960s, Nambu’s first attempts at laying out a framework of mathematical equations to unify gravity and the other forces gave rise to the beginnings of string theory. But in the overall history of investigations into particle physics, Nambu’s work – rather, his intellect – was a keystone. Without it, the day theorists’ latinate squiggles on paper could’ve become prize-fetching particles in colliders would’ve been farther off, the day we made sense of reality farther off, the day we better understood our place in the universe farther off.
The Osaka City University, where Nambu was a professor, announced his death on July 17, due to an acute myocardial infarction. He is survived by his wife Chieko Hida and son John. Though he was an associate professor at Osaka from 1950 to 1956, he visited the Institute for Advanced Study at Princeton in 1952 to work with Robert Oppenheimer (and meet Albert Einstein). Also, in 1954, he became a research associate at the University of Chicago and finally a professor there in 1958. He received his American citizenship in 1970.
Peter Freund, his colleague in Chicago, described Nambu as a person of incredible serenity in his 2007 book A Passion for Discovery. Through the work and actions of the biggest physicists of the mid-19th century, the book fleshes out the culture of physics research and how it was shaped by communism and fascism. Freund himself emigrated from Romania to the US in the 1960s to escape the dictatorial madness of Ceausescu, a narrative arc that is partially reflected in Nambu’s life. After receiving his bachelor’s degree from the University of Tokyo in 1942, Nambu was drafted into the army and witnessed the infamous firebombing of Tokyo and was in Japan when Hiroshima and Nagasaki were bombed.
The destructive violence of the war that Nambu studied through is mirrored in the creative energies of the high-energy universe whose mysteries Nambu and his peers worked to decrypt. It may have been a heck of a life to live through but the man himself had only a “fatalistic calm”, as Freund wrote, to show for it. Was he humbled by his own discoveries? Perhaps, but what we do know is that he wanted to continue doing what he did until the day he died.