‘In his youth Albert Einstein spent a year loafing aimlessly. You don’t get anywhere by not “wasting” time – something, unfortunately, which the parents of teenagers tend frequently to forget.’ So begins the first lesson of the international bestseller Seven Brief Lessons on Physics. It was something that its author, Carlo Rovelli, learned in his youth as I was to discover as we sat chatting one morning about physics, philosophy and writing during a recent visit to London.

Although it only appeared in English in October, Rovelli’s latest book, Reality Is Not What It Seems, was published in Italy at the beginning of 2014, before he wrote a series of articles on fundamental physics for an Italian newspaper that were turned into Seven Brief Lessons on Physics, a work he calls his ‘little book’. Its eighty-three pages have been translated into forty-one languages and in the UK the paperback edition is riding high in the Sunday Times bestseller list. Its success has turned the ever-youthful, mop-haired and mild-mannered Italian theoretical physicist into a much-sought-after celebrity scientist.

In truth, Rovelli has been a celebrated scientist for some time. Last May a week-long conference was held at Aix-Marseille University in the south of France, where he has worked for the past fifteen years, to mark his sixtieth birthday. This ‘Carlo Fest’ sought to honour his pioneering work in developing a theory of quantum gravity that attempts to reconcile general relativity and quantum mechanics, the two theories that in the 20th century led to a re-evaluation of our ideas about space and time, and matter and energy. ‘It’s here that the magic of 20th-century physics begins,’ Rovelli says. ‘Studying and trying to understand them in depth is a bewitching adventure.’

As we discuss the difficulties of trying to describe the counterintuitive aspects of reality at the quantum level to others, Rovelli laments, ‘The problem of quantum physics is that we do not know how to explain it to ourselves.’ But the situation regarding general relativity couldn’t be more different. Conceived by Albert Einstein, it is an elegant and coherent vision of gravity, space and time. It is, says Rovelli, ‘the most beautiful theory produced by physics’ and ‘comparable to Mozart’s Requiem, Shakespeare’s King Lear or Michelangelo’s ceiling in the Sistine Chapel’. General relativity shows that the Earth moves around the Sun not because a mysterious invisible force pulls it, he explains, but because ‘space bends and curves under the weight of matter’.

For the past thirty years, Rovelli has been one of the pioneers of loop quantum gravity, a theory that ‘describes the quantum properties of space-time’ and also offers ‘a conceptual understanding of what quantum space and quantum time could be’. Applying this theory, he and his collaborators have speculated that space is not a continuum, that it is not divisible ad infinitum and that there exists a minimum volume of space. This quantum of space (or ‘atom of space’ or ‘quantum loop’) has a diameter of 10^-33 cm – that’s a million-billion-billion-billionth of a centimetre. Beyond this unimaginably small distance, called the Planck length after the German physicist who discovered the quantum, nothing exists.

Rovelli believes that loop quantum gravity is ‘the best theory of quantum gravity we have at present’. He points out that it’s not a ‘theory of everything’ because it does not include a description of the other three forces known to exist: the weak and strong nuclear forces and electromagnetism. Quantum gravity is one of the most difficult and esoteric areas of theoretical physics; it can also spell career suicide. ‘I was fascinated by anything radical, extreme, fundamental, revolutionary,’ explains Rovelli. ‘And here was a problem that seemed to question the very structure of the world, the notions of space and time.’ It seemed a natural choice for a young man who, as he tells me, was in rebellion.

Rovelli was born in Verona in 1956. His father was an engineer who ran a small construction company, while his mother ‘was perhaps too enamoured of her only child’. By twenty he had already run away from home at least once, dropped out of school and gone travelling for a year through Canada and the USA. In the 1970s, Rovelli confesses, he dreamed of changing the world: ‘I was close both to the hippy dreams of peace and love and to radical left political movements.’ He helped to run a pirate radio station and was sometimes in trouble with the police. He tells with a hint of pride that he still has the court order authorising the search of ‘all my dwellings for suspected “subversive association”’. Like many others before and since, Rovelli discovered that youthful ‘dreams of easily making a more gentle and more just world evaporated rapidly’. It was only then that he took refuge in theoretical physics: ‘I completely fell in love with this stuff.’ He admits that until that time he had been a ‘lazy student’ and that the decision to study physics at Bologna University had been made ‘a bit at random’.

At the end of his university studies, aged twenty-five, Rovelli was imprisoned for refusing to do compulsory military service. ‘I was detained only a few days,’ he explains. ‘I was lucky because in those days the Italian government was sending soldiers abroad – to Lebanon – for the first time since the Second World War, without real support from the public. So they did not want people like me making waves and decided to let me go.’ He had expected to spend up to two years in prison, having ‘decided that this was much better than one year in military service’.

‘Loafing aimlessly’ and a bit of youthful time wasting have paid off handsomely for Rovelli, as they did for Einstein. ‘I started writing almost for myself,’ he explains. ‘My first book grew out of my notes on the Greek philosopher Anaximander.’ It is quickly apparent when talking to Rovelli that he has a fondness and a deep appreciation for the ancient Greek philosophers. He calls Anaximander, who lived in the sixth century BC, ‘my greatest passion outside theoretical physics’.

What Rovelli finds remarkable and captivating about Anaximander, whom he labels the ‘first scientist’, is that he understood that ‘the Earth is a finite body that floats in space, without falling, and the sky is not just over our head; it is all around’. The genius of Anaximander was to effectively ask, ‘Why should it fall?’ ‘In other words, he realises that the obvious generalisation from every small heavy object falling to the Earth itself falling might be wrong. He proposes an alternative, which is that objects fall towards the Earth, which means that the direction of falling changes around the Earth.’

Some physicists, such as Stephen Hawking, have dismissed the idea of philosophy having any role to play in science. It’s an attitude Rovelli disagrees with: ‘I think that the reciprocal exchanges between physics and philosophy have always been very fruitful to both sides in the past, and can still be so.’ The physicists he most admires, from Newton to Einstein, took philosophy seriously and it heavily influenced their work. ‘I think that being dismissive of philosophy betrays superficiality,’ he says. ‘It usually betrays the fact one holds a specific naive philosophy, thinking this is the only possible alternative.’

When I ask how he finds the time to write, he says simply, ‘My entire life has no routine, but often I wake up early in the morning and start writing. Essentially I use all bits of free time I can collect here and there. Lots of writing during long aeroplane flights.’ He says that he enjoys reading all sorts of different things, except contemporary novels, which he finds boring, but he loves classic novelists, including Conrad. He’s reading Proust at the moment because he wants to write a book about time, though he is not quite sure when or how. ‘I think that there are many different kinds of science writings,’ he says. ‘There is science writing to simply popularise, and science writing to actually present new ideas or new perspectives. I do a bit of both. There is science writing that offers many details and science writing that tries only to communicate the core: the main central ideas, and the passion. The second is what I do.’

‘I write because I have found out that people are interested in things I say. It is a strange feeling. All my life I have felt I have ideas not shared by many, but for a time long nobody cared much about my ideas.’ He is taking advantage of the fact that it is now easier for him to be heard. The leading Italian newspaper Corriere della Sera asked him to write for them. Rovelli only accepted after being reassured that he could write about social and political issues as well as science and would be free to express positions contrary to the newspaper’s own.

‘Since quantum events are no longer ordered by the passage of time at the Planck scale, time, in a sense, ceases to exist,’ says Rovelli. Unfortunately, at the everyday scale of things we’ve run out of time. Later, while reading Reality Is Not What It Seems, I come across a passage that seems to encapsulate much of what Rovelli tries to do in physics and his writing: ‘Science is made up of experiments, hypotheses, equations, calculations and long discussions; but these are only tools, like the instruments of musicians. In the end, what matters in music is the music itself, and what matters in science is the understanding of the world which science provides.’