Physics is said to go deeper than other sciences into the riddle of existence. The laws of physics — gravity, energy, motion, time — underpin those of chemistry, astrophysics and meteorology combined. So an understanding of the world requires a basic understanding of physics; something which has just become a little easier thanks to a cult book by an Italian academic which is due to be stuffed into an extraordinary number of stockings this Christmas.

Seven Brief Lessons on Physics, by Prof Carlo Rovelli, has already sold more copies in his native Italy than Fifty Shades of Grey. The English translation has become Penguin’s fastest-selling science debut ever. In less than 80 pages, Ravelli’s slim poetic meditation seeks to clarify the troubling uncertainties of Einsteinian relativity, quantum theory and other physical exotica. Not since Stephen Hawking’s (admittedly hard-going) Brief History of Time has there been such a consensual success in the science book market. So far, rights have been sold in 28 countries, including Turkey, Egypt and China. How has Rovelli done it?

When I meet him, he is still struggling to come to terms with his Piketty-like success. ‘My aim was always to write my book for the layman,’ he says. In fact, his book started as a series of newspaper articles — the idea was to write only about the most interesting bits. ‘I decided to focus on the beauty of modern physics and cut out everything which sounded dull.’

In this, he continues a tradition of jargon–free scientific writing from Galileo to Darwin — an art which disappeared in the academic specialisation of the last century.

In the first of his book’s lessons, Rovelli explains Albert Einstein’s general theory, formulated 100 years ago last month. Aged just 36 years old at the time, Einstein set out a theory of gravity that superseded Isaac Newton’s and treated time and space as essentially the same.

In Rovelli’s elucidation, the Earth moves round the Sun because of the distortion of ‘space-time’ by the Sun’s greater mass. An analogy represents ‘space-time’ as a rubber sheet distorted by a heavy ball representing the Sun; a smaller ball rolling by, representing a planet, will tend to fall into this depression, apparently attracted. In Einstein’s universe, this is what is known as gravity.

Nobody said that post-Newtonian physics was easy, but Rovelli writes of ‘warped time’ and other tentative physics with bracing clarity. That’s not to say that the lay reader won’t be a bit baffled at times.

‘That’s normal,’ he says: the human brain is not designed to deal with galaxies or the invisible world of atoms. ‘We think that our minds are all-powerful. But in reality, they’ve evolved to do what we need to do —like hunt, eat and talk to one another.’

It is only in recent years that science has become, in publishing terms, popular and attractive. Before Rovelli, the Italian writer-scientist Primo Levi sought to make chemistry accessible in his literary–scientific commentary The Periodic Table, which reached the UK bestseller list in 1985 alongside Dick Francis. Rovelli said he revered Levi for his ‘lapidary integration of science and literature’. His own book displays a very Levi-like enthusiasm for knowledge of all kinds, ranging from King Lear to neuro-science to James Joyce.

Educated at a liceo classico (classical school) in Verona, Rovelli is known for his work on loop quantum gravity theory and Anaximander, a pre-Socratic Greek philo-sopher. He is impatient of religious fundamentalists of any denomination — and the idea that science is ever settled. ‘Physics questions everything all the time,’ he says. ‘I don’t believe anyone who says we’re close to the final theory of anything.’ Scientists such as Richard Dawkins who pretend to atheist omniscience are, he says, no less intolerant or prejudiced. ‘If I am allowed to be polemical, the world is not necessarily as Dawkins thinks it is.’

Science, he says, is not about certainty. ‘It’s about finding the most reliable way of thinking at the present moment. At any moment we have a vision of reality that is effective, it’s good, it’s the best we have found so far. But, at the same time, it’s not taken as certain, and any element of it is a priori open to revision.’

Rovelli adds: ‘I find beliefs hard to believe, not because I know the answers — no one does. Why should a militant atheist know better than a lapsed Catholic like me?’

Newtonian certainties were further disturbed when Einstein predicted that time passes more quickly ‘high up’ than below, nearer to the Earth. So if a man who has lived at sea level meets his twin who has lived in the mountains, he will find that his sibling is slightly older than him.

The notion that time does not pass identically for everyone unsettles Catholic church hierarchies even today, says Rovelli. Of course, back in the 17th century, the church had warned curiosity-driven researchers like Galileo not to put divine laws to the test. ‘It’s scarcely against nature to be curious,’ Rovelli told me. ‘It is in our nature to be so.’

He says familiarity with Latin, combined with a wilful ignorance of science, is a mark of social status in Italy. ‘Most of those at the top of Italian society today have been to a liceo classico. I wrote my book with them very much in mind,’ he adds.

Rovelli is taking aim at what C.P. Snow called the ‘Two Cultures’ of science and the arts. Writing in the 1960s, Snow argued that the world of words and of numbers were slowly divorcing — with potentially disastrous effects for basic human understanding — and that the scientists would become boffins, unable to communicate outside their milieu, and that the rest of us would give up even attempting to understand science.

‘I see no incompatibility between the two cultures, only mutual attraction,’ Rovelli insists. This is his belief: that non-specialists are fascinated by science, if only it can be explained properly. The sales of his book suggest that he might just be right.