Professor James Stirling CBE FRS

When James Stirling left Durham University in 2008, he could look back on two decades of remarkable work. His research on the behaviour of subatomic particles, specifically the so-called monojet anomaly, in which protons failed to behave as they were supposed to in a particle collider, had been a triumph.

The hitherto unexplained anomaly had raised hopes of uncovering a new physics that could combine Einstein’s relativity with quantum mechanics to form the elusive “theory of everything”. Yet Stirling had seen, with characteristic clarity, that the puzzle was much simpler than others had realised. There was to be no new physics.

At the same time he had dedicated himself to remaking the way physics was studied at Durham. He created a new institute, the Institute for Particle Physics Phenomenology, one of two parts of the new Ogden Centre for Fundamental Physics, and became its inaugural director.

He secured funding for the institute, which was a coup for the small, if well-regarded, Durham physics department, beating rivals at Oxford and Manchester and turning the university into a world-renowned centre of particle physics.

From there, Stirling went on to become Durham’s first pro-vice- chancellor for research. With the same vision that he brought to physics — and showing notable kindness towards his juniors — he steered the research staff through difficult periods. Somehow he achieved this without throwing his (considerable) authority around. None of his colleagues remember him so much as raising his voice.

After 22 years in the northeast, however, he was ready to leave. He told a friend that he was going to Cambridge, where he had been appointed the Jacksonian Professor of Natural Philosophy, to refocus on research.

He enjoyed the organisational, administrative stuff, but missed being able to concentrate on how the innards of a proton worked. His friend smiled at his naivety. “As soon as you set foot in Cambridge,” he told Stirling, “they’re going to make you head of the Cavendish Laboratory.” “No, no,” Stirling responded firmly. “I’m going there to do physics.”

Soon afterwards he was, as predicted, the head of the Cavendish, arguably the most famous physics laboratory in the world, where the neutron and electron were discovered.

William James Stirling was born in Belfast in 1953, the son of John and Margaret Stirling, who were primary-school teachers. He was educated at the Belfast Royal Academy at the height of the Troubles; an IRA bomb blew in the windows of his office while he was working at the now-defunct Northern Irish Milk Marketing Board after finishing his A levels.

A bright, hard-working youth, he was accepted to do the mathematical sciences tripos at Peterhouse, Cambridge, although he had many interests far from the science lab. He was a gifted rugby player and musician, able to turn his hand to almost any instrument, especially the piano, trumpet and guitar. After graduating with first-class honours he went on to do a PhD in theoretical particle physics, the study of the most basic building blocks of the universe. From there he undertook postdoctoral research at the University of Washington in Seattle, then at Cambridge, before heading to Cern in Geneva.

Although he came from mathematics to physics, Stirling was not a pure theoretical physicist. He focused on the “phenomenology” of particle physics — the border between theory and experiment; what the mathematics predicted that experiments would reveal. He published more than 330 articles in scientific journals, and several were among the most cited in the world of particle physics. Indeed, his findings underpin much of the work done on the Large Hadron Collider at Cern.

His most famous work was on the monojet anomaly. Researchers using particle colliders noticed that when they smashed protons into protons at an extraordinary fraction of the speed of light, something strange happened. The mathematics predicted that when two of them collided, they would emit two particles, visible as “jets” on the screen, but they often showed only one. There was much excitement. Some thought it was a hint of new physics, perhaps superstring theory, which is the great hope for combining relativity and quantum physics.

Stirling, though, saw the simplicity at the heart of the matter. One of the particles that the proton often spat out in these collisions, he noted, was a fundamental particle called the Z boson; Z bosons can “decay” into neutrinos. Neutrinos, which have no charge and are a million times smaller than an electron, are almost impossible to detect. The particle was there, it was just flying off without leaving a trace. Both Z bosons and neutrinos are part of the Standard Model of particle physics, so there was no need to start looking for exciting new paradigms. Stirling explained why the unexpected was expected.

Stirling also made a great impact in other fields during a career marked by a series of firsts: as well as being the first director of the Institute for Particle Physics Phenomenology and Durham’s first pro-vice-chancellor for research, he was the first chairman of the Particle Physics and Astronomy Research Council science committee and the first provost of Imperial College London. While at Durham he also endeared himself to students by inaugurating what became known as the “Stirling break”, a three-minute pause in the middle of lectures, which students would tend to employ as an opportunity to gossip.

He spent the last five years of his career — and almost, as it was to prove, of his life — at Imperial, and immediately set about improving the diversity of its staff. He was especially concerned about gender equality, and created a new post, provost envoy for gender equality, and, later, an assistant provost for diversity and inclusion. By the time he left the post in early 2018, colleagues found that the whole “mood music” had changed at Imperial; it had become a far more amenable place for women to work.

Despite spending two thirds of his life in England, Stirling remained proud of his Irish, and Northern Irish, identity. He retained his Belfast accent, while he and his wife, Paula (née Close), a fellow academic, kept a house on the border with the Republic and had Irish passports. Throughout his life he returned to their old Belfast school to talk to pupils, most recently in March. He was also a passionate supporter of the Irish national rugby team.

He had met Paula at school, where she was in the year below him. They married when he was 22, in part because his parents, who were religious, would have frowned upon a long cohabitation. The couple grew together, and had their first child, Tom, while they were in Seattle in 1981; Helena was born in Cambridge two years later. They all survive him. Tom works in communications for the police, while Helena is a GP in Northern Ireland.

Stirling tried hard to maintain a life outside of the universities where he worked. Staff at Imperial became used to the sight of his four grandchildren overturning his office while Stirling looked on indulgently. He and Paula would go to their house in Ulster for as many weekends as they could, flying out on Friday and returning on Sunday, after kayaking and walking, and seeing Helena and her two children.

He also continued to play music. At Durham he set up a physics ceilidh band in which he played guitar; and at Imperial he befriended the head of the next-door Royal College of Music, pushing for ever more collaboration between the two institutions.

Imperial was his final post, and he stepped down in August 2018. With grown-up children and young grandchildren, and homes in Northern Ireland and Durham, he and Paula had great plans for a long retirement. However, two months before he left Imperial Stirling was diagnosed with an aggressive cancer. He died five months later.

One colleague, writing a memorial for one of Stirling’s former universities, suddenly found the “admins” getting in touch. They said: you’ve spoken about his brilliance, but you’ve omitted how kind he was in big ways — he would spend time with the bereaved parents of students who had died — and small; he once dedicated an afternoon to helping a junior lab technician find the best spots to go walking on holiday in Co Durham. Senior academics do not always leave a good impression on their administrative staff. This was not the case with Stirling.

A week after he died Ireland played New Zealand in Dublin. For the first time in the 113-year history of the fixture, Ireland beat the All Blacks at home. It was a game that Stirling would have enjoyed.

Professor James Stirling, physicist, was born on February 4, 1953. He died of cancer on November 9, 2018, aged 65.