Isaac Newton Lecture explores ground-breaking physics in memory of Sir Thomas Kibble
8 December 2016
The life and work of Professor Sir Thomas Kibble was the subject of a commemorative lecture at the IOP’s London premises on 30 November.
Kibble had been named as the winner of the Institute’s Isaac Newton Medal but died in June before learning of his award. The Isaac Newton Lecture was given in his place by his longtime friend and colleague Professor Kellogg Stelle of Imperial College London.
Stelle’s lecture described Kibble as an “architect of microphysics and the universe”, and he added: “Tom was a friend for many years – all the time I’ve been in Britain, in fact.”
Stelle recounted how Kibble had been born in 1932 in what was then Madras and is now Chennai, India, and been educated in one of the best schools in what was at the time the province of Madras Presidency. While there he gained a love for geometry from the patterns of Moghul architecture.
At the age of 10, Kibble set sail for Britain to continue his schooling – making the journey alone and with just two days’ notice. During a stopover in Capetown, South Africa on a voyage lengthened by the wartime closure of the Suez Canal, Kibble went ashore only to return and find the ship had gone – but only to another dock. Stelle said that such incidents gave Kibble a certain sense of self-reliance.
Kibble attended Melville College, Edinburgh and, after an unsuccessful attempt at the Cambridge scholarship exam – for which he found the problems “tedious” – went to the University of Edinburgh.
He remained in Edinburgh to study for a PhD under John Polkinghorne and during that time married Anne Allan. The pair would have three children, Helen, Alison and Robert, who were in the audience for Stelle’s lecture and who collected their father’s Isaac Newton Medal at the IOP awards dinner the previous evening.
After having completed his PhD, Kibble received a fellowship to spend a year in the US, heading to Caltech, where he got to know Richard Feynman and Murray Gell-Mann. Returning to the UK, he joined the Theoretical Physics Group at Imperial – which is where he would do the work for which he is best known, on unification and symmetry-breaking, over 1964–67.
Kibble had seen that one of Imperial’s advantages was that its reputation and location allowed it to easily attract visitors, Stelle explained. Under the influence of Professor Abdus Salam, the construction of unified gauge theories became a major aspect of the university’s work in theoretical physics, and in 1964–65 Gerald Guralnik and Dick Hagen were there as visitors – and would take part in a critical collaboration with Kibble.
Quantum theory had been integrated with Maxwell’s electromagnetism to form quantum electrodynamics, which was based on gauged symmetry. But attempts to take the same approach to explaining the strong nuclear force failed.
In particular, the short ranges of that and the weak interactions implied that the particles responsible for carrying those forces must have a mass, whereas those in gauge theories were naturally massless. Simply adding a mass term into the equations introduced infinities that it was not possible to cancel out.
The ideas of how to successfully introduce masses into gauge fields were introduced into field theories from another area of physics – superconductivity. They were based on spontaneous symmetry breaking.
Stelle explained that although with hindsight it may appear that those models lead directly to Professor Peter Higgs’s work, in practice it wasn’t that simple. A particularly notable failure was that they incorrectly made the photon massive.
In 1962, Salam, Jeffrey Goldstone of the University of Cambridge and Steven Weinberg showed that, in general, spontaneous breaking of rigid symmetries leads to massless bosons, posing a problem for those working on relativistic field theories. “This is unacceptable for real physics, as no such massless boson was known,” Stelle said.
This was resolved in 1964 by three groups who independently recognised that Goldstone’s theorem can be evaded in gauge theories. The paper by Robert Brout and François Englert was the first to be published; that by Higgs was the only one to include a massive scalar boson, now famously named after him but not thought important at the time; and the one by Kibble, Guralnik and Hagen gave the most complete treatment.
In 1967, Kibble wrote a paper that Stelle described as “magisterial”, which set out the complete mathematical structure of spontaneous symmetry breaking and the Brout-Englert-Guralnik-Hagen-Higgs-Kibble mechanism, which added to existing theory an extra quantum field permeating all space, which, below some extremely high temperature, causes spontaneous symmetry breaking. That paper “really explained the theory as we now see it”, Stelle said, and that same year Salam and Weinberg incorporated the mechanism into what would become the standard model of particle physics.
But Kibble had not been the only physicist to discuss which vector fields acquire masses and which remain massless. The previous year, two 19-year-old undergraduates in Moscow, Alexander Arkadyevich Migdal and Alexander Markovich Polyakov – unaware of much of western research from behind the iron curtain – had independently reproduced some of the same work.
Stelle said that this lack of uniqueness was taken into account by the Nobel committee in deciding to award the 2013 Nobel Prize only to Higgs and Englert. “Tom really deserves the credit for explaining how all this works,” he added. Nevertheless, all six authors of the three 1964 papers were recognised with the 2010 Sakurai Prize of the American Institute of Physics.
In the 1970s, Kibble wrote another influential paper on the consequences of spontaneous symmetery breaking, this time concerning the formation of topological defects – such as magnetic monopoles or cosmic strings – in the very early universe.
After data on the Cosmic Microwave Background (CMB) from the COBE satellite became available, Kibble and others considered models for the formation of structure in the early universe seeded by cosmic strings. More precise data collected later ruled out this possibility, showing that cosmic strings can account for no more than 10% of the CMB structure. However Kibble’s ideas on defects were verified in a very different context – in the formation of vortices in superfluid Helium-3B.
During his life, Kibble served as vice-president of the Royal Society, the patron of Scientists for Social Responsibility and as chair of the Martin Ryle Trust. As well as the Sakurai Prize he was honoured with numerous awards including the IOP’s Rutherford and Guthrie medals, the International Centre for Theoretical Physics’s Dirac Medal, the Albert Einstein Medal, and the Royal Society of Edinburgh’s Royal Medal. He was knighted in 2014 – but originally tried to turn it down, relenting only at the request of his children (pictured with Stelle). It was one of many examples, Stelle said, of the humble man that Kibble was.
A video of the lecture is available to view online.