Canterbury's Emeritus Professor Roy Kerr - one of the world's greatest living mathematicians - turned 90 years old on Thursday. Photo / George Heard
He’s among the world’s greatest living mathematicians. And at age 90, Emeritus Professor Roy Kerr is still as curious as ever about the mysteries of the cosmos. Jamie Morton reports.
It looked like a flaming doughnut; or perhaps an orange eye, peering out at us from the cold depths of space.
For science, the first-ever image of a black hole, unveiled to an awestruck world a little more than five years ago, was an instant revolution.
For Roy Kerr, this cosmic behemoth, ringed by a halo of dust and gas at the heart of a galaxy 55 million light years from Earth, represented something a little more personal.
“It was incredible to look at,” he recalled.
“And it agreed with theory.”
Not just anyone’s theory, but his own, which, for 50 years has been a cornerstone of general relativity and cited by the field’s greatest minds.
The Kerr Solution, a mathematical description of spacetime around spinning black holes, has been called the “most important exact solution to any equation in physics”.
As such, Kerr was name-checked in Stephen Hawking’s bestseller A Brief History of Time, and remains the only Kiwi to have received the prestigious Einstein Medal and Crafoord Prize.
Just for the mathematical mountain Kerr scaled, his peers here argue his should be a household name, mentioned in the same breath as Hillary or Batten.
But Kerr, who turned 90 last Thursday, doesn’t seem fussed at all about that.
His focus has always been on the numbers, if not just seeing that they correctly add up.
“If there’s been anything in my life that I’ve been good at, it’s picking out rubbish.”
It’s a marvel in itself that Kerr ever made it to the world stage of theoretical physics.
Like Ernest Rutherford before him, he was born in a tiny South Island town - Kurow served as the base for building nearby Waitaki Dam – amid “the slump” of the early 1930s.
His mother walked out on his unfaithful father shortly before the outbreak of World War II, and the family later shifted to rural Gore.
“How hard did I work in school? I didn’t do any work, but I did read a hell of a lot of books from the library.”
There weren’t any about maths, but the young Roy realised he had an unusual knack for it when counting rubber bands at his father’s Christchurch business.
“I could count 25 and put them in a bag in six seconds.”
St Andrew’s College provided little to nurture his talent – “there was no physics teacher and the chemistry teacher was a failed lawyer” – but he doggedly studied his way straight into third-year mathematics at Canterbury University College.
The young prodigy naturally excelled, despite working from a 19th-century syllabus – and found himself crash-coursing modern physics after he arrived at Cambridge University in the mid-1950s.
A collaboration with a fellow student on a paper, concerning the long-standing two-body problem, paved the way for his thesis and one of his first splashes in academia.
“I was working totally alone, without a supervisor, which from a practical point of view might have seemed a bit of a nuisance,” he said.
“But I saw it as a big advantage, because I didn’t have people telling me how I should do things, or what was or wasn’t true.”
Before leaving Cambridge, he crossed paths with Peter Bergmann, the physicist best known for his work with Albert Einstein, and who was then attempting to bring together quantum mechanics and general relativity.
On a giant sheet of paper, Kerr began crunching the numbers to find that what Bergmann was hypothesising simply couldn’t work.
“I told him this and I’m pretty sure he believed me: I was offered a job soon after.”
Eventually, he took up a post at the University of Texas at Austin – also once home to the trail-blazing New Zealand astronomer Beatrice Tinsley – which proved the backdrop to his defining breakthrough.
It began with a paper by a rival group at Syracuse University and Kerr quickly deduced they’d made clumsy errors in their calculations.
His own answer to the same problem offered the first exact solution to Einstein’s equations defining the space outside a rotating star or black hole.
Scientists hadn’t been able to crack it for half a century, and many, including Einstein himself, doubted it could be done.
Kerr remembers the morning he worked through his equation, as the department’s renowned founder Alfred Schild sat by in his office armchair, patiently puffing on a pipe.
Soon enough, Kerr looked up from his workings and turned to tell Schild: “It’s rotating!”
Sixty years on, physicists still consider Kerr’s solution an astonishing achievement.
“Almost everything in the universe, from planets to stars and galaxies, have some spin,” explains University of Auckland cosmologist Professor Richard Easther.
“Whenever a black hole forms, it inherits the spin of the material used to construct it - so every actual black hole in the universe needs Roy’s solution to describe it properly.”
University of Canterbury theoretical physicist Professor David Wiltshire, a former student of Hawking’s, said it remained the “workhorse” for disentangling images of spinning black holes captured by the Event Horizon telescope – just like that first one in 2019.
A few years earlier, when scientists announced they’d detected long-theorised cosmic ripples called gravitational waves, Kerr’s black hole solution had also had a role.
Pairs of black holes act much like cosmic eggbeaters, producing gravitational waves as they orbit each other. This slowly brought them together, until they formed a single object.
“The product of that merger is always a spinning black hole, and we are getting to the point where we can test Roy’s solution by looking at the patterns of waves produced by these mergers,” Easther said.
Wiltshire said that, back in the 1960s, physical intuition told [Kerr] that the problem of understanding what happens inside black holes was horrendously complicated.
“Not worth pursuing back then,” he said, “but with terabytes of new data, high performance computing and the incisive ways Roy taught us to think, steps to these goals are now falling into place.
“The quantum gravity revolution will surely last a few decades still. New Zealand is no longer the periphery; with Roy Kerr’s solution we are now helping define the shape of things to come.”
Easther expected that, for as long as there were scientists to talk about black holes, they’d be using Kerr’s equations to do it.
“From a New Zealand perspective, we have just a handful of people who cast as big a shadow as Roy; it’s a Hillary-level achievement and we should absolutely know his name.”
Remarkably, Kerr’s latest paper came just a few months ago, and ruffled feathers across the physics world by challenging the popular notion that all black holes possess regions of infinite density called singularities.
“It was as if an apparently quiet volcano suddenly started producing steam and then roared into life,” Easther said of the paper, which quickly drew global headlines.
Having made a landmark discovery at the height of general relativity’s golden age, Kerr might well have gone on to even greater things in his field.
Instead, stricken by Lyme disease, and depressed and disillusioned by petty politics and rivalry in science, he decided to head home to Christchurch in the early 1970s.
“I did go back [to Texas] once, but I hated it.”
He found himself much happier heading and transforming the University of Canterbury’s mathematics department, a role he held until his retirement in 1993.
Just across the campus, at the physics and astronomy department, his seminal work on the Kerr Vacuum provided the basis of much research and teaching.
Outside academia, Kerr put his brain toward another mathematical formula: developing a new bidding system for contract bridge, of which he became a noted player.
His bridge days are now well behind him, he says, but there are plenty of other important things in his life: not least Margaret, his wife of five decades.
His exact solution to a happy marriage?
“Do what you’re told ... but I don’t always,” he says with a chuckle.
The couple have nine children and a dozen grandchildren.
Kerr says many of them, unsurprisingly, have forged their own paths into mathematics and science, while one granddaughter is pursuing another family passion.
“She’s going to be a veterinarian and loves animals ... so do we,” Kerr says, noting Margaret, a dog breeder, had 21 golden retrievers on their section at one point.
He finds time to attend a seminar once a week at his old university but acknowledges his brain is slowing down fast; some days, a game of Sudoku is enough of a mental workout.
Still, he’s happy to speak his mind about the crisis in our universities: “If I was a professor in New Zealand, I’d be looking elsewhere.”
As for physics, he says it’s been a thrill seeing data captured by powerful new telescopes begin to test long-standing theories about the cosmos.
Before his time’s up, he’d love to see an answer to the enduring enigma that is dark matter, but suspects science will shift away from dark energy, the force supposedly pushing outward to expand the universe.
Then there’s that conundrum that Bergmann grappled with all those decades ago: making the systems of quantum mechanics and general relativity agree with each other.
“To me, that’s the big one. If we had an answer to that ... we’d have it made.”
And what of a higher power? Did spirituality hold any appeal in his twilight years?
Certainly not.
He once told his headmaster he was an atheist just to be excused from singing hymns - and his stance on religion hasn’t budged since.
“Look, I don’t understand the universe or how everything fits together,” he adds.
“But when somebody tells me that they do know, I just don’t believe they know what they’re talking about,” he said.
“I’ve got three young cats that I adore, and I suppose that if I’ve got any gods, it’s the pussy cats.”
Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.
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