Peter Higgs (1929–2024): A Gentle Giant of Science
We have lost an important scientist; we have also lost a wonderful man.
Peter Higgs was a gentle man who wanted a quiet life. However, fate had other plans for him. In 1964, after returning to his home in Edinburgh after a failed weekend camping trip, he hit upon an idea that was to become one of the most important building blocks of the Standard Model of particle physics: the Higgs mechanism. In 2012, the Higgs particle that his theory predicted was finally discovered at the European Laboratory for Nuclear Physics (CERN), thus providing the experimental underpinning of the physical models that describe three of the four fundamental forces of nature.
Higgs wrote up his idea in a two-page scientific paper entitled “Broken Symmetries and the Masses of Gauge Bosons.” It was initially rejected by the major European physics journals, as having no obvious relevance to physics. But then he added a paragraph mentioning a possible observable consequence of his idea and submitted his paper to the American physics journal, Physical Review Letters, where it was published on 19 October 1964. Similar ideas were explored by the physicists Robert Brout and François Englert, and independently by Gerald Guralnik, C.R. Hagen, and Tom Kibble, and these two groups also published their work in the same journal. But, perhaps as a result of that extra paragraph that predicted a physical consequence of his theory, it was Higgs’s name that became associated with the hypothesis, which ended up providing the cornerstone of the successful effort to unify two of the four known forces in nature: the weak and electromagnetic interactions.
The concept that Higgs and the others developed built upon an idea that Nobel Prize-winning condensed matter physicist Philip W. Anderson had applied in the context of superconductivity—the phenomenon whereby certain materials, when cooled below some critical temperature, become perfectly conducting, with zero electric resistance. In fact, it is easiest to understand the idea in this context.
Electromagnetism, the force that underlies almost all the physical processes governing chemistry and life on Earth, is a long-range force. The force of repulsion between two negatively charged electrons can be felt, albeit weakly, right across the visible universe. In our modern, relativistic quantum physics understanding of the universe, forces are conveyed by the exchange of virtual particles. Electromagnetism, in this model, is understood as being due to the exchange between electrons of virtual photons, the quanta of electromagnetism. Real photons are the elementary quanta that make up light, and all observable electromagnetic phenomena.
According to this understanding, electromagnetism is a long-range force because photons have no mass, and therefore virtual photons can be exchanged between electrons that are arbitrarily far apart and only a vanishingly small amount of energy is required for the exchange.
Superconductivity is one of the most remarkable quantum mechanical phenomena that can be observed in macroscopic materials. It took almost 50 years after its experimental discovery for a theoretical explanation of superconductivity to be developed. (In 1913, Heike Kamerlingh Onnes received a Nobel Prize in Physics for the discovery of superconductivity; John Bardeen, Leon N. Cooper, and J. Robert Schrieffer were jointly awarded the 1972 Nobel for their development of a theory of superconductivity.)
Lawrence M. Krauss
The theoretical explanation involved the formation of a special quantum state full of “Cooper pairs”—pairs of electrons which, under certain conditions, find it energetically favourable to condense and bind together, and once they do, can flow unimpeded through material.
One of the many weird properties of superconductors is that electromagnetic fields cannot permeate them. A strong electric field will die off exponentially just beneath the surface of a superconducting material. This is called the Meissner effect. It happens because when photons propagate inside the material through this special Cooper-pair state, the photons behave as if they are massive, not massless, particles. But forces conveyed by massive particles must be short range, not long range, so the electromagnetic field dies off quickly inside the surface of the material.
Higgs (alongside Brout, Englert, Guralnik, Hagen, and Kibble) realized that a similar phenomenon can occur for relativistic quantum fields in elementary particle physics. In this case, instead of electron pairs condensing within a material, a quantum field associated with a new elementary particle could condense into the vacuum of empty space. The resulting background field permeating all of space could have a profound effect. Previously massless particles interacting with this field would have their flow impeded, as if they were now massive, just as photons inside a superconductor act as massive particles.
At the time, this may have seemed like simply an interesting curiosity, which is perhaps why the journal Physics Letters rejected Higgs’ paper. However, three years later, Steve N. Weinberg and, independently, Abdus Salam, resurrecting an older model proposed by Sheldon Glashow, realized that this “Higgs mechanism” could allow the unification of electromagnetism with the weak force, which acts inside nuclei and is responsible for nuclear radioactivity.
It had been shown that the equations describing the weak force could be put in a form that resembled that of electromagnetism, except that the carriers of the weak force, particles now called the W and Z particles, would be very massive, over 80 times as massive as protons. The problem was that if one added an explicit term into the equations to give these particles a mass, the resulting theory ended up predicting nonsense, with numerous interactions becoming infinitely strong.
What Weinberg and Salam realized in 1967 was that if there was a new background quantum field in nature, the Higgs field, and if W and Z particles interacted with the field, then even if at a fundamental level these particles were massless, as long as the Higgs field existed throughout space, the particles would behave as if they were massive. If photons didn’t interact with the Higgs field, they would remain massless. In this way, the W and Z particles and photons could be unified in a single theory. If the Higgs field didn’t exist in nature, all the particles would be massless, and the two forces would look identical. But if the Higgs field existed, the W and Z particles would appear massive, the weak force would suddenly become short range, only able to manifest on nuclear or smaller scales, while electromagnetism would remain the long-range force we know and love today. Even more remarkably, perhaps, the Higgs field could be seen as responsible for the observed masses of almost all elementary particles in nature. Those that interacted strongly with this field would behave as if they had a large mass; those that interacted more weakly would get a smaller mass; and those that didn’t interact at all would get no mass.
In 1979, Weinberg, Salam, and Glashow were awarded the Nobel Prize for their unification of electromagnetism with the weak force, and in 1984 the W and Z particles were experimentally discovered at Cern and Carlo Rubbia and Simon van der Meer won that year’s Nobel Prize in Physics for the discovery.
All that remained to fully verify the electroweak unification was the discovery of the quanta associated with the mysterious new Higgs field. In 2012, the Higgs particle was experimentally observed at CERN, the same place where the W and Z particles had been discovered, thus completing one of the most beautiful theoretical and experimental sagas in modern particle physics.
Although he appreciated the beauty of this discovery, on a personal level, Higgs was not thrilled. He later said that the discovery of the Higgs particle, which led to his subsequent Nobel Prize in 2013 (with François Englert) “ruined his life.” He was not a man who courted the limelight and he had lived in relative anonymity, as someone only known to the physics community, for almost 50 years. He was not amused when, in 1993, the Nobel Prize-winning physicist Leon Lederman wrote a popular book dubbing the Higgs the “God Particle,” since the Higgs field would have made our observable universe possible, full as it is of massive particles and the matter they make up. Lederman later said he had meant to call the particle the “Goddamn Particle,” but his editor made him change the name. Having known and worked with Leon, I suspect that this was a joke—but we will never know.
All of us who knew Peter recognized that he was a kind, quiet and gentle man, who enjoyed his theoretical and mathematical pursuits and the camaraderie of his colleagues. I first met him in Scotland in around 1980, when I was attending a summer school on particle physics, at which Glashow, and two subsequent Nobel Laureates, Gerard ‘tHooft, and Barry Barish, also lectured. Peter preferred to remain in the background, sharing pleasantries with the rest of us, even with lowly graduate students like me (I was doing my PhD at the time).
His kindness and humility made as strong an impression on me as the important theoretical discovery with which his name is associated. For Higgs was a gentleman as well as a scholar. That is the highest praise I can give anyone—and I dispense it only rarely. We have lost an important scientist; we have also lost a wonderful man. It is an honour and a privilege to have known him.
%3A%20A%20Gentle%20Giant%20of%20Science){kind=link}