RIP Peter Higgs, who laid foundation for the Higgs boson in the 1960s

Peter Higgs, the shy, somewhat reclusive physicist who won a Nobel Prize for his theoretical work on how the Higgs boson gives elementary particles their mass, has died at the age of 94. According to a statement from the University of Edinburgh, the physicist passed "peacefully at home on Monday 8 April following a short illness."

“Besides his outstanding contributions to particle physics, Peter was a very special person, a man of rare modesty, a great teacher and someone who explained physics in a very simple and profound way," Fabiola Gianotti, director general at CERN and former leader of one of the experiments that helped discover the Higgs particle in 2012, told The Guardian. "An important piece of CERN’s history and accomplishments is linked to him. I am very saddened, and I will miss him sorely.”

The Higgs boson is a manifestation of the Higgs field, an invisible entity that pervades the Universe. Interactions between the Higgs field and particles help provide particles with mass, with particles that interact more strongly having larger masses. The Standard Model of Particle Physics describes the fundamental particles that make up all matter, like quarks and electrons, as well as the particles that mediate their interactions through forces like electromagnetism and the weak force. Back in the 1960s, theorists extended the model to incorporate what has become known as the Higgs mechanism, which provides many of the particles with mass. One consequence of the Standard Model's version of the Higgs boson is that there should be a force-carrying particle, called a boson, associated with the Higgs field.

Despite its central role in the function of the Universe, the road to predicting the existence of the Higgs boson was bumpy, as was the process of discovering it. As previously reported, the idea of the Higgs boson was a consequence of studies on the weak force, which controls the decay of radioactive elements. The weak force only operates at very short distances, which suggests that the particles that mediate it (the W and Z bosons) are likely to be massive. While it was possible to use existing models of physics to explain some of their properties, these predictions had an awkward feature: just like another force-carrying particle, the photon, the resulting W and Z bosons were massless.

Over time, theoreticians managed to craft models that included massive W and Z bosons, but they invariably came with a hitch: a massless partner, which would imply a longer-range force. In 1964, however, a series of papers was published in rapid succession that described a way to get rid of this problematic particle. If a certain symmetry in the models was broken, the massless partner would go away, leaving only a massive one.

The first of these papers, by François Englert and Robert Brout, proposed the new model in terms of quantum field theory; the second, by Higgs (then 35), noted that a single quantum of the field would be detectable as a particle. A third paper, by Gerald Guralnik, Carl Richard Hagen, and Tom Kibble, provided an independent validation of the general approach, as did a completely independent derivation by students in the Soviet Union.

At that time, "There seemed to be excitement and concern about quantum field theory (the underlying structure of particle physics) back then, with some people beginning to abandon it," David Kaplan, a physicist at Johns Hopkins University, told Ars. "There were new particles being regularly produced at accelerator experiments without any real theoretical structure to explain them. Spin-1 particles could be written down comfortably (the photon is spin-1) as long as they didn’t have a mass, but the massive versions were confusing to people at the time. A bunch of people, including Higgs, found this quantum field theory trick to give spin-1 particles a mass in a consistent way. These little tricks can turn out to be very useful, but also give the landscape of what is possible."

Ironically, Higgs' seminal paper was rejected by the European journal Physics Letters. He then added a crucial couple of paragraphs noting that his model also predicted the existence of what we now know as the Higgs boson. He submitted the revised paper to Physical Review Letters in the US, where it was accepted. He examined the properties of the boson in more detail in a 1966 follow-up paper.

Higgs later admitted that he did not initially realize how significant his theory would turn out to be. "It wasn't clear at the time how it would be applied in particle physics, and those of us who did the work in '64 were looking in the wrong place for the application," he said. And he wasn't the only one. "Nobody else took what I was doing seriously, so nobody would want to work with me," he said. "I was thought to be a bit eccentric and maybe cranky." Higgs only published a handful of papers after those early contributions and told The Guardian in 2013 that these days, he would probably not be considered productive enough to warrant a university professorship.

Fortunately, other physicists were able to build on Higgs' early work. By 1967, Steve Weinberg had extended the Higgs mechanism to account for the mass of electrons and heavier leptons, and in 1971, Gerard ‘t Hooft and Martinus Veltman figured out how to get rid of a few annoying infinities in some of the equations. By 1983, the W and Z bosons had had their masses determined, providing an experimental validation of some of the predictions made by the theoreticians.

It took the construction of the Large Hadron Collider at CERN to experimentally detect the elusive signature of the Higgs boson. On July 4, 2012, CERN hosted two seminars, streamed live around the world, announcing the long-awaited discovery of the Higgs boson based on data from two different yet complementary experiments (ATLAS and CMS) —the last piece of the Standard Model puzzle. Higgs, then 83 and retired, was at CERN when the discovery was announced, largely thanks to CERN physicist John Ellis, who left Higgs a phone message: "Tell Peter that if he doesn't come to CERN on Wednesday, he will very probably regret it."

The assembled scientists gave a standing ovation when the talks were over, and a visibly emotional Higgs pulled out a handkerchief and wiped away a tear. "During the talks, I was still distancing myself from it all, but when the seminar ended, it was like being at a football match when the home team had won," Higgs later recalled. "It was like being knocked over by a wave." But he didn't stick around for the afterparty, preferring to celebrate on the flight home with a can of London Pride beer.

Higgs received his first nomination for the Nobel Prize in Physics back in 1980; the possibility that he might win one day was the main reason, he claimed, that he didn't get the sack from the University of Edinburgh. That day arrived in 2013 when Higgs shared the Nobel Prize with Englert "for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles...."

Not liking fuss, he planned to leave town for the West Highlands, but his car battery was dead. He went for lunch in Leith instead, and when a neighbor saw him and broke the news of his award, he jokingly feigned ignorance and said, "What award?" Higgs turned down a knighthood in 1999, but Queen Elizabeth II appointed him to the Order of the Companion of Honor in 2013.

“Even though he didn’t much enjoy it, he felt a responsibility to use the public profile his achievements brought him for the good of science, and he did so many times," University College London physicist Jon Butterworth, a member of the ATLAS experiment, told The Guardian, calling Peter Higgs. "a hero to the particle physics community. The particle that carries his name is perhaps the single most stunning example of how seemingly abstract mathematical ideas can make predictions which turn out to have huge physical consequences.”

Higgs is survived by two sons, Chris and Jonny, daughter-in-law Suzanne, and two grandchildren. His wife, Jody, from whom he was separated, died in 2008.