Julian Barbour’s obsession with time began on Oct. 18, 1963. The 26-year-old Cambridge graduate in mathematics was on a train to the Bavarian alps, where he and a friend planned to climb the Watzmann, Germany’s third highest peak. The newspaper in his hand contained a summary of a Scientific American article by British physicist Paul Dirac. “He questioned whether four-dimensional symmetries are a fundamental feature of the physical world,” Barbour recalled. Dirac was pulling apart Einstein’s conception of the three dimensions of space and one of time, looking for deeper truths. The next day, Barbour woke with a headache and told his friend he was in no state to climb. “I said, ‘You’ll have to go up the mountain on your own.’” Left alone with his thoughts, Barbour sat and asked himself “What is time?”
Barbour assumed the question came from Dirac’s writing, but he later re-read the article, and the question wasn’t in there. “There’s not a word about Dirac asking what time is. I must have invented that to give myself the confidence to challenge this thing,” he said. “I suppose I thought that, if Dirac had said it, it must be worth taking on!”
The question of the nature of time, so big he couldn’t quite claim it for himself, would dominate Barbour’s life. In 1999, he published his initial conclusion, The End of Time, which declared time to be an illusion that has no place in the fundamental description of how the universe works. The book was variously described as “provocative” and “fascinating.” In The New York Times, Simon Saunders, a philosopher of physics, hailed it as “a masterpiece.” But the most gratifying reaction was surely that of John Archibald Wheeler, the stellar (in every sense) physicist who coined the term “black hole.” Wheeler said, “Plato and Aristotle, if they had read this book, would still be discussing it.”
This April, as he sat in the kitchen of his 360-year-old house in Oxfordshire, England, Barbour, 84, was still discussing the concept of time with the excitement of a 26-year-old. In December, 2020, he published The Janus Point, his first book since The End of Time. It’s named after the two-headed Roman god who simultaneously looks forward and backward. Barbour’s thesis is that the Big Bang, which he calls the Janus Point, seeded the flow of time in two directions. Time “no longer has one direction, from past to future, but instead has two: from a common past at the Janus point to two futures in the two directions away from it,” Barbour writes.
Lee Smolin, a faculty member at the Perimeter Institute of Theoretical Physics, called The Janus Point “simply the most important book I have read on cosmology in several years … both a work of literature and a masterpiece of scientific thought.”
“Plato and Aristotle, if they had read this book, would still be discussing it,” John Archibald Wheeler said.
I’m not as well-placed to judge as Smolin, but the book does feel refreshing and different: a closely argued, substantive take on one of the biggest unsolved mysteries of physics, written by someone who has wrestled with not only the physics, but also the history and philosophy relevant to his subject. What’s more, Barbour’s approach, unlike many in the popular science game, is to publish only when he thinks he has something worth saying. That alone is enough to make him worth listening to. Not that it’s easy to get to grips with his central thesis, as Barbour anticipated. That’s why his book contains extra white spaces between paragraphs in places: Here, Barbour writes, readers can pause “for a tea or coffee break.” But rather than have tea by myself at home, I decided I would learn more by having tea with the author himself. Barbour was very happy to oblige.
When he greeted me at his front door, Barbour embodied the quintessential English country gentleman at leisure. He was wearing a fleece gilet zipped over his russet sweater. His slate corduroy trousers were slightly short in the leg—he is a tall, slim man. His feet were covered by thick light gray socks shoved into Birkenstock sandals. He was quick to smile and laugh. He had the air of someone who used to captain the school cricket team.
Before he made waves in the physics world, Barbour was not an academic superstar. At Cambridge he earned what he called “a rather ordinary second-class degree,” and then opted to take a year off to go and live in Munich to improve his German (at a school run by the man who had been Hitler’s chief interpreter, it turned out). There he met Peter Mittelstaedt, a young academic who had been Werner Heisenberg’s student. “He invited me to do a Ph.D. with him,” Barbour said. Barbour wanted to research Ernst Mach’s ideas about the nature of time, but Mittelstaedt said, “No, that’s much too risky—you probably won’t get anywhere, and you’ll never get a job.” Instead, Barbour wrote his Ph.D. on general relativity. “Frankly, my thesis was a very modest affair,” he said.
Despite ditching Mach, he remained convinced that he would never hold down an academic job. When he had to make a decision about it, he asked an acquaintance what would be expected of him if he took a research post. The answer—to publish one or two good papers a year–horrified Barbour. “I said there’s no way I’m going to be able to do that.”
Giving up on the idea of academia, Barbour came back to England. Having learned Russian while in Germany, Barbour began to earn a living translating classic Russian physics papers for Plenum Publishing in New York and the American Institute of Physics. “It was very boring work but a steady income,” he said. “And it left about a third of my time free to develop my ideas.” To further satisfy his intellectual cravings, Barbour became a hanger-on at physics conferences, feeding on the ideas and digesting them in his spare time. “I liken myself to a bee going to get nectar from academia,” he said.
Barbour writes at a custom-made semi-circular desk in his house, College Farm, which he bought from Oxford University’s New College in November 1963. He can see his childhood home from College Farm’s first floor windows. Both buildings, like most of the village, are constructed from a golden stone that seems to have been designed to capture and re-radiate late afternoon sunshine; the setting is, a real-estate agent would say, idyllic. As if to confirm this, there is a sign mounted on the side of Barbour’s house. It points toward the back, and proclaims that somewhere down there lies Arcadia, the mythical idyll of the ancient Greeks. Next door to College Farm, the other side of the path to Arcadia, is the church of St. Peter ad Vincula, built in the 12th century. It’s not hard to imagine a young Hugh Grant rushing through the churchyard in a morning suit and mumbling apologies for being late again. This is the England of Four Weddings and a Funeral, of John Betjeman, of stopped clocks. Which is appropriate for a man who has spent most of his life battling time.
Barbour suggests that art might provide a better guide to the true nature of the universe than science.
In many senses, declaring time to be illusory was the low-hanging fruit. Our deepest theories suggest that time is not fundamental to the universe: It doesn’t really figure, except as a marker of change, in quantum physics. In relativity it is malleable, its moments undefinable across the universe. The big question left open is what causes our experience of time’s arrow—the one-way flow of moments. Barbour has explained what he thinks is the answer in The Janus Point. That answer, he said, has lain in plain sight, waiting to be discovered since the late 18th century.
In 1772, the French mathematician Joseph-Louis Lagrange made an extraordinary discovery. Approximately, it’s this: Imagine there are three particles moving around and interacting only via Newton’s law of gravity. Lagrange showed that the size of this total system—the diameter of an imaginary circle that encloses all three particles—will vary in a very odd way. The diameter will shrink to a minimum at some moment in time, then grow again—forever. The whole three-particle system never returns to that minimum size.
Amazingly, Lagrange’s result works for any number of particles. And when Barbour read about it, he thought it might work for an entire universe; after all, what is a universe but a load of particles swirling about? If true, this would mean that the universe hit a minimum size at some point, and then grew ever afterward. And that minimum is what we think of as the moment of the Big Bang. In Barbour’s Janus-headed universe, time runs in two directions, away from that point of minimum size. Lagrange’s proof of a minimum size, he said, gives us a cause for the arrow of time. Why do we experience time only running forward? Because we’re moving away from Lagrange’s minimum, and a mathematical law says we can never return there.
“I’ve been interested in the arrow of time for almost as long as I can remember, and nobody has ever come up with a suggestion that a law of the universe says there must be one,” Barbour said. “It’s extraordinary that it has been sitting there for four centuries.”
While Barbour is bullish about what he has pulled together from his studies of the history of science, it’s not clear to other physicists that the Janus Point idea solves the problem of time’s arrow. For a start, it is a purely classical idea that makes little sense in terms of a more fundamental approach such as quantum field theory. What’s more, Barbour’s model ought to, but can’t explain the origin of the initial fluctuations in the stuff of the universe, which are essential to explain the large-scale structure that astronomers have observed with exquisite precision. And so, while the arguments can sound convincing to some, cosmology insiders are generally wary of giving the Janus Point too much credit.
Such critiques won’t deter Barbour from pursuing his ideas. Even now, with two masterpieces under his belt, he is not done. He is physically fit, and walks for more than an hour every day. Some things are slowing down, he admits—he has to re-read the previous day’s work before he can continue to write, for instance—but he is undaunted by age. “I think the things that really count, the conceptual ideas, are fine,” he said. And so, like time, he is always moving forward. “There’s two more books I’d like to put out,” he said. One is a history of thermodynamics that he has already half-written. The other is a new, typically ambitious, idea for uniting Einstein’s relativity with quantum physics to create a single “quantum gravity” framework for describing the cosmos. “It came to me literally as I was writing the final chapter [of The Janus Point],” he said.
The root of this new idea owes a debt to his original inspiration: the Austrian physicist Ernst Mach. Deep study of Mach’s work has led Barbour down the road of formalizing a theory with his various collaborators. He summarizes the essence of it as asking, “What sort of initial data do you need to predict what the future will be?” The key, Barbour said, is to make sure you consider the expansion of the universe. “That brings all the interesting structure, formation and everything,” he said. He is excited by the possibility that developing this idea will solve the measurement problem of quantum mechanics as well as uniting quantum theory with relativity. He also thinks, even more controversially, that it could identify meaning in the universe. “If this new idea about time and quantum gravity is correct, I think that is possible.”
Finding the meaning of the universe is not something that most scientists would consider to be within their remit. The convention is that artists, writers, and philosophers are the ones to bring us meaning. But Barbour seems happy to swap the roles of science and the arts. He even suggests that art might provide a better guide to the true nature of the universe than science. In The Janus Point, he writes that human moments of deep creativity “might be subliminal inspirations from the whole universe,” and that a performance of a great operatic aria can capture something of the cosmos as neatly as any mathematical equation. He sees humans as actors in the universe’s drama, describing himself as “a participant in whatever the universe does.”
Whether academic colleagues see him as a scientist, a thinker, a writer, or a provocateur, Barbour is a much-appreciated participant in the scientific universe. He is an optimist and an idealist: His character is not that of the hard-nosed, always-skeptical ivory-towered researcher. He is a glass-half-full guy; he admits to being a Platonist who believes in the existence of ideals—an Arcadia hiding somewhere down a sun-dappled lane—that we can’t quite see. The pursuit of this elusive idyll seems to be what makes him tick.
“Nobody has ever come up with a suggestion that a law of the universe says there must be an arrow of time.”
This may be why the 17th-century German physicist and philosopher Gottfried Leibniz kept coming up in our conversation. It’s not so much Leibniz’s thoughts on time that seem to interest Barbour; it’s much more about Leibniz’s view of the universe. Leibniz suggested that pursuit of perfection is the ultimate underlying purpose of the universe’s unfolding. Voltaire mocked Leibniz for suggesting that we live in the best of all possible worlds, but Barbour shares Leibniz’s view. In many ways, Barbour’s life’s work is a continuance of Leibniz’s effort to justify idealism despite our experience of life. “I’m inclined to think, with Leibniz, that there is more good than bad in the world,” he told me.
During our conversation, Barbour couldn’t find the right word to summarize Leibniz’s philosophy. The next morning at 7:35 he sent me an email. “The word I was looking for is theodicy,” he said. It means justifying God, the attempt to show that there is no inherent reason why the existence of evil rules out the existence of a good, omnipotent deity. There does seem to be a theodicy at the heart of Barbour’s work: with the universe moving away from its minimum, all things can and must happen; you have to tolerate evil if you want good to exist. As Barbour puts it in the book, “There is no light without the dark.”
And, at 84, perhaps he is in a good position to judge. Through experiences that range from mountain-climbing to being in the room when a young theoretical physicist first presented the idea we now call Hawking Radiation, to dealing with his wife’s suffering with Alzheimer’s disease, he has learned that making the most of time is what matters. His kitchen is peppered with pictures of his grandchildren, and he uses Zoom to talk to at least one of his children, who live, respectively, in France, Argentina, and South Africa, almost every day. Family means more to him than ever; Barbour recently lost his wife and, even more recently, a daughter (they are memorialized together in the dedication of The Janus Point).
At the end of our conversation, I raised the physicist Carl Sagan’s suggestion about meaning: that our lives, however insignificant or painful they seem, have a cosmic significance because humans are the means by which the universe achieves knowledge of itself. “I’ve never read Carl Sagan,” Barbour said.
It’s easy to feel daunted, perhaps a little unschooled, in Barbour’s presence. His knowledge of the history of physics has a vast scope, much broader than almost anyone working in the field. His gift is that he knows what has been thought, and what has been said, and he finds ways to synthesize those insights and draw new ideas out from within their implications. But Barbour is open to new ideas too. “I think Sagan’s was a good hunch,” he said.
Michael Brooks is a United Kingdom-based science writer, and the author of The Quantum Astrologer’s Handbook.