Thomas Kibble

Professor Sir Thomas Kibble, who has been posthumously awarded the IOP’s Newton Medal, was instrumental to the discovery of how certain particles acquire mass.

Professor François Englert and Professor Peter Higgs were awarded the 2013 Nobel Prize in Physics for their work in this area, with Higgs claiming that Kibble should have been “an obvious candidate” to be a third winner.

Their work resolved a problem that had troubled particle physicists in the 1960s. According to the symmetries thought to govern particle physics, the gauge bosons – the particles responsible for transmitting the fundamental forces of nature – should be massless. And yet the W and Z bosons that carry the weak nuclear force were observed to have large masses.

This was problematic: it looked as though an otherwise highly successful theory of particle physics was inherently flawed. But symmetry laws aren’t always obeyed – they can be broken in certain conditions. In 1962, Professor Philip W Anderson proposed that precisely this would happen, below a certain temperature, if a particular kind of field permeated all of space.

In 1964, the details of exactly how this works were independently published around the same time by three research groups – by Englert and Professor Robert Brout, by Higgs, and by Kibble, Professor Gerald Guralnik and Professor CR Hagen. Their work was recognised in a collection of milestone papers gathered for the 50th anniversary of Physical Review Letters in 2008, and the six physicists were awarded the Sakurai Prize in 2010.

Brout and Englert’s paper was published first, that by Kibble, Guralnik and Hagen is considered the most detailed, and Higgs was the only one of the six to predict the existence of the particle now named after him – the Higgs boson.

By the early 1970s, Professor Steven Weinberg and Professor Abdus Salam had fully incorporated the Englert–Brout–Higgs–Guralnik–Hagen–Kibble mechanism into the standard model of particle physics. Weinberg was also the first to realise that the mechanism is also responsible for the class of particles known as fermions, which includes electrons, neutrinos and quarks.

The new theory accurately predicted the existence of many particles that had never been seen until they were produced in particle accelerators. Among them, the Higgs boson was discovered at CERN in 2012. Kibble, therefore, was central to some of the most inspiring physics of the early 21st century.