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© James Ferguson

Waves of photons, travelling at the speed of light, left the sun on the journey towards a warm London eight minutes ago. At roughly the same time, Professor Carlo Rovelli arrived ahead of schedule for our lunch, sat down at our table, ordering a lemonade and opening a copy of the literary periodical the London Review of Books, which I find him reading, having ordered another lemonade, on my irradiated arrival.

Rovelli is among the world’s foremost theoretical physicists. He specialises in quantum gravity, a theory that attempts to solve what he describes as “one of the big open problems” in physics. His work is sufficiently important for a five-day conference, “Carlo Fest”, to have been held in May to mark his 60th birthday. But the reason he has joined the ranks of the celebrity scientist is his gift for popularising immensely complex science.

His book Seven Brief Lessons on Physics was a bestseller in his native Italy in 2014 and has now been translated into English. Based on a column published in the Italian newspaper Il Sole 24 Ore, it makes the head-spinning world of protons, electrons, gluons, quants, hot black holes and discontinuous time elegantly comprehensible to the general public.

At Clarke’s, he is dressed in short-sleeved black shirt and trousers. His tousled grey hair grows darker at the temples, as though denoting the intense mental activity that goes on between them. He wears glasses to read the menu and resists my cajolements to let his appetite run wild — by picking, say, the Exmoor caviar for two at £67 — with a modest choice of the buffalo mozzarella salad with a salad of runner beans and purple figs, Cornish leaves and balsamic dressing. To drink, H2O is preferred over C2H6O, in this instance a glass of wine.

The location, a Kensington mainstay, is airy and whitewashed, with a hum of background conversation. Rovelli sits under a blue semi-abstract print by Howard Hodgkin called “Frost”. Elsewhere, out of sight, are several drawings by Lucian Freud, who visited Clarke’s almost every day.

Picked by his UK publishers, the choice of location reflects Rovelli’s cultural interests, although the art goes unnoticed. It also takes account of various Rovellian dislikes. These include noisy restaurants, spicy food and — unusually for an Italian who lives in the south of France — garlic.

“In my family there was no garlic,” he says in English, adding that he inherited his father’s loathing of the Mediterranean staple. But his generous, open manner conforms to another aspect of national stereotype. “I’m Italian,” he says with a smile, “so you can ask me whatever you want.”

I announce that I would like to start by contesting a proposition in Seven Brief Lessons on Physics with which I do not agree.

“Oh,” he says, surprised. “Are you a scientist?” No, I reply with due ceremony, I am the FT’s pop critic. Rovelli laughs; not in the contemptuous way of a snooty don at the high table, but in the wary mode of one who is not quite sure what he has let himself in for.

The passage from the book that I proceed to quote concerns his denunciation of “the incomprehension and distrust of science shown by a significant part of our contemporary culture”. On the contrary, I suggest, the cultural standing of scientists has never been higher. Fantasies of the lab-coated geek or sinister genius have been superseded by visions of heroic intellectual achievement. Resources also favour them. In 2010, UK government funding for sciences at universities was ringfenced while humanities suffered deep cuts.

“You know, I think you’re right,” he concedes, hands on the table, fiddling with his dessert spoon and fork as though conducting a gentle experiment into friction. “But it’s recent, I would say. And the UK is probably the country least touched by that [suspicion of science]. A lot of culture in France and Germany is dominated by high Gregorian ideas that true knowledge is not scientific knowledge, science is sort of second class. And it’s worse in the US. I mean, come on, when many Americans don’t believe in evolution or climate change, I think there’s a problem with anti-science.”

Our waiter materialises with the food, placing the buffalo mozzarella salad before Rovelli. The cheese has been flown in from Naples, as have the tomatoes that accompany my lobster salad, which arrives with a shrubbery of rocket leaves and avocado.

Rovelli pronounces his dish “good” but does not elaborate further. In terms of physics, it is the plainest on the menu, requiring the least energy in its passage from base material to upmarket restaurant meal.

“I like simple food,” he says. “I live by the sea, I wake up in the morning and see the Mediterranean. I have a little boat, I go out with bread, cheese and tomatoes, and I’m happy.”

Home is Cassis, the picturesque seaside town near Marseille, where he works at the Centre for Theoretical Physics at Aix-Marseille University. Previous university posts have been in Italy and the US.

“Science has different styles,” he says between mouthfuls of salad. “American universities are extraordinarily open to new ideas. Disagreement is much more tolerated and encouraged. But Europe sometimes gives more space for going your own way.”

The best country for conducting robust scientific debate is Germany. “That’s the beauty of it. They just look you in the eye and say, ‘I disagree, you’re wrong.’ Everything is much more complicated and foggy and muddy in France. You don’t go to a big professor and say you disagree — he gets offended.”

German was the main language for physics until the rise of Nazism. Is there any value, I ask, to reading a scientific text in its original language, like reading Marcel Proust in French rather than translation?

“How did you know I’m reading Proust!” Rovelli cries, shrinking back into his chair as though confronted by a scientifically inexplicable act of telekinesis.

It turns out he is currently rereading A la recherche du temps perdu, in French, having first done so when he was a student. He laughs at the uncanny coincidence. (As for reading scientific texts in the original: “Scientists don’t usually do so, and it’s a mistake, I think they should, to see how the idea came out.”)

In Seven Brief Lessons about Physics, Rovelli compares an Einstein equation about the curvature of space to “the rarefied beauty of a late Beethoven string quartet” and places the general theory of relativity on the same level as Shakespeare’s King Lear or the Sistine Chapel. In 2011 he published a biography of the ancient Greek philosopher Anaximander.

“The best part of the Italian culture has a Renaissance tradition of bringing things together, starting with Galileo,” he says, forking at a fig. “Some of the literary critics in Italy believe Galileo is the best prose writer. At root is the idea that a man of learning should know all the culture, whatever he does. I’m certainly not alone among the Italian physicists who have studied Latin, Greek, history of philosophy. And that’s rare outside Italy.”

He was born in Verona in 1956. His father, an engineer, created a construction company, symbolic of Italy’s rise from wartime rubble to modernity.

“My father is a very intelligent man, soft, not an academic,” he says. “My mother stayed home, like women used to do at the time, and took care of the child, I was the only child. My mother is also an extremely intelligent woman but also very passionate. They both came from the bourgeoisie but not very high bourgeoisie.”

It was an affectionate upbringing, a “perfect family”, but Rovelli rejected its conventions as a teenager. “I was rebellious in the way of the 1970s. At some point I started growing my hair. I did not want to go to university, in fact. My plan was to be a beggar, like a vagabond.”

The maître d’, patrolling the room, glides over to refill glasses of water and offer bread, which we both accept. Rovelli returns to telling me about his winding route to theoretical physics.

He chose to study the subject at Bologna University, “a largely random” choice of degree course. To his parents’ dismay, he was a listless science student, preferring to read works of literature and philosophy. He also threw himself into Bologna’s radical politics. The mid- to late-1970s were a time of mounting confrontation between the city’s Communist-led government and its students, leftist “autonomists” who opposed authoritarianism.

“We very naively thought we were part of a huge movement that would create more equality and justice and peace in the world,” Rovelli says. “And this movement was wide because it went from Marxist-Leninist all the way to hippy pacifists smoking marijuana and singing Hare Krishna.”

At 20, after one year of university, he spent nine months hitchhiking around Canada and the US, inspired by Beat writers. It was a life of Pink Floyd, utopianism and taking LSD, the whole countercultural ideal.

“Sure,” he says. “LSD was important to us. It was something taken seriously. It was a very good education, to not trust the received ideas and try something a little different. That, I think, played a role. Also, the wilderness period gave me, and many others in fact, the courage to go away. And in science, you need that.”

Our plates, both emptied of contents at a leisurely pace, are cleared away. “You know, I may have a dessert,” Rovelli says. He quickly chooses the lemon balm panna cotta with gooseberries and croquante d’amande.

I ask for his help in picking the most advanced pudding in terms of physics. It turns out to be the affogato, in which hot espresso coffee is poured over vanilla ice cream. “It’s fighting against the second principle of thermodynamics,” Rovelli explains. “It’s a desperate tentative attempt to stop time from happening. It’s what I’m trying to do in my physics.” In other words: my ice cream will melt.

Rovelli’s love for physics followed a similar transfer of energy in the late 1970s, sparked as his faith in politics and the counterculture cooled.

“Science was a path for me from that,” he says. “In a sense, in science you can create revolutions, things do change. Our vision of the world has changed.”

The area he was drawn to is one of the thorniest in theoretical physics. Quantum gravity attempts to reconcile the two pillars of 20th-century physics: quantum mechanics, first formulated by the German physicist Max Planck in 1900, and the general theory of relativity, unveiled by Planck’s friend Albert Einstein in 1915. Each insight about the workings of time, space and gravity is fundamental to modern physics. However, neither fits together neatly.

Gravity is one of the points of contradiction. A theory called “loop quantum gravity” that Rovelli has done vital work to develop with his colleague Lee Smolin, who he describes as “my best friend and collaborator”, addresses that contradiction. If proven, it would represent one of the holy grails of physics.

“The theory is more or less there, it is written,” he says. “There are things we don’t understand yet, but the question is how you test it.”

If it can be found to work, then Rovelli’s peers who have spent their careers working on a rival approach, string theory — about which Rovelli is respectfully dismissive — would find all their toil and sacrifice come to nothing. “It’s like playing football,” he shrugs, “either you win or you lose.”

Our desserts arrive. Like a tentative lab assistant (“So this is how I do it, right?”), I pour the coffee on to my vanilla ice cream under Rovelli’s gaze. The second law of thermodynamics goes to work as the ice cream undergoes an irreversible process of entropic breakdown.

“That’s your life, right?” Rovelli observes genially, spooning up some panna cotta.

Looking ahead, he anticipates breakthroughs in his quantum gravity research: “I used to think, ‘Well, I’m not going to see it in my life.’ And now, I hope, before dying, to have seen some result.”

He has a girlfriend, an ex-student who works as a physicist in the Netherlands. He was married once but it ended 15 years ago. “We had a plan: life, family, children and all that,” he says. The plan did not work: he has no children. He went through “a difficult period” in the aftermath of the marriage ending but that lies behind him. “My life has always been up and down. Now I’m 60 and I feel great,” he says.

In October, Reality Is Not What It Seems will be published, the English translation of a 2014 book. He is plotting a new book about time, which is why he is rereading Proust. He recognises the criticism that pop-science books can be a diversion from the serious work of research. But science, for Rovelli, does not exist in a vacuum.

“If you work on something like theoretical physics, you feel like you’re trapped inside a room, and there’s all these writings, and outside people don’t know,” he says. “You have a desire to tell, a natural desire to tell, plus you’re getting people who are saying ‘What are you doing, can you explain?’ ”

The panna cotta has been polished off and the affogato’s life-and-death struggle has been transferred to my stomach. A sunny afternoon in London beckons for Rovelli, then it will be back to Marseille and the efforts to transform our way of seeing the universe.

“Quantum gravity is a problem that has resisted for surprisingly long,” he says. “Electricity, how atoms work, what is light — these are all big problems at which humanity has hesitated in the past, but then the solution has come up. That’s the beauty of science, right?”

Ludovic Hunter-Tilney is the FT’s pop critic

Illustration by James Ferguson

Copyright The Financial Times Limited 2018. All rights reserved.