by Nikita Ostrovsky
In conversation with the physicist and writer, Carlo Rovelli.
Does Nature know when we’re watching? Our common-sense view of the world vehemently denies the possibility. If a tree falls in the woods and no one hears it, it still falls; so say philosophers, at least, from Aristotle to the guy on Cornmarket Street shouting something through a megaphone. Suggest otherwise, and you end up with the plot of Toy Story — inanimate objects acquiring a life of their own the moment your back is turned. The problem is, since the mid-1920s, physicists haven’t been so sure.
Quantum mechanics (QM) is the most accurate physical theory we have. It can describe both stars and atoms. It has given us smartphones, lasers and computers. And it has left us with the uneasy feeling that the world behind our backs may be different to the one we see. The predictions of quantum mechanics are strange, but unequivocal: a physical system (in common parlance, a “thing”) behaves in one way when left alone, in another when observed. Unlike most philosophical problems, this one is not an abstract paradox. It has been tested many times, yielding the same confounding result.
In a double slit experiment, two slits are placed in front of a screen. When an electron is fired through these double slits, it hits the screen behind and leaves a mark. As the experiment proceeds, thousands of pinpricks appear on the screen and a pattern resolves. Many regularly spaced fringes — narrow, parallel stripes — begin to appear, bright lines where electrons have hit in greater numbers, dark regions where they are mostly absent.
Why do the electrons not hit the screen directly behind the slits, like sand running through your fingers accumulating beneath the gaps? In an attempt to answer the question, we repeat the experiment with a detector behind the left slit. Every time an electron passes through the left slit, the detector clicks; each time it passes through the right, it does not. This, truly, is where our vision of reality breaks down: half the time, the detector clicks; half the time it does not. Now, when we look at our fringes, they are gone — in their stead, two stripes: sand sifted through a child’s fingers. This astonishing result has been reproduced countless times in laboratories around the world. Each iteration reaffirms the predictions of quantum mechanics: measurement, no matter how delicately performed, invariably alters the result of the experiment.
Niels Bohr, a founding father of quantum mechanics, proposed the ‘impossibility of neatly separating the behaviour of atomic systems from their interaction with the measuring device’ — in other words, reality depends on our observation. But this seems to drag us back to an outdated anthropocentrism, articulated by physicist John S. Bell in 1987: ‘Was the wavefunction [the state of a system as described by QM] of the world waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer, for some better qualified system ... with a PhD?’ ‘Try yourself to think of a sensible explanation for this behaviour,’ writes Carlo Rovelli. ‘For a century now, we’ve all been trying.’
Carlo Rovelli is sixty-five, but he sounds like a much younger man. ‘The place most significant to me ends up commonly to be where I currently am. I am in love with the here-and-now,’ he tells me from his current base in “fake” London, Canada. ‘My girlfriend has a faculty position here at the university, so a couple of years ago we decided to buy a house here … and here is great because, you know, here is Canada,’ his soft Italian accent amusingly fluctuating to North American. ‘From the window we just see trees. It’s perfect.’ As we speak, his voice spans octaves, falling to emphasise an important point, rising in uncertainty when I provoke his scepticism. Throughout, there is an undercurrent of gentle energy. Early on, I ask how long he would like to speak — expecting to be allotted twenty minutes, if I’m lucky. ‘That’s okay, I’m not in a hurry,’ comes the cheerful reply, ‘just take your time.’
From a man of Rovelli’s cultural stature, this is unexpected (although not out of character: my instinct to refer to him in hushed tones as “Professor Rovelli” is quickly suppressed by his email signature of “Carlo” or “C”). He is the director of a research group at Aix-Marseille University on loop quantum gravity (LQG), a theory at the cutting edge of theoretical physics. ‘I am attached to the idea that my true identity is having tried to understand quantum gravity all my life, and my best work by far is my contribution to loop quantum gravity,’ he says. He is wistful when speaking about his work as a physicist: ‘I want some consequences of the theory (loop quantum gravity) to be testable before I die,’ he says, chuckling softly, ‘that’s my desire.’
It was Rovelli’s writing, however, that brought him into the public eye. The 96-page Seven Brief Lessons on Physics (2014) elevated Rovelli to minor celebrity: over a million copies sold in forty-one languages. Since then, four more books have cemented his place in the canon of research physicists writing for the lay reader, alongside Stephen Hawking and American Nobel Laureate Richard Feynman. Still, he is sanguine about his writing: ‘It never came specifically as a choice to start to write, it happened a little bit by chance. I started writing for a large public very late in life, after I was fifty. I always thought, maybe I’ll do that in the future, first I have to do science. But then the desire of presenting the way I was viewing things was a big motivation.’ He has also worked on the philosophy of physics, most notably, a 1996 paper titled Relational Quantum Mechanics, published in the International Journal of Theoretical Physics. Helgoland (2021) presents those ideas to a general audience for the first time.
Rovelli is not a cookie-cutter physics populariser. He has a mischief and an intellectual diversity that distinguishes him from his predecessors. He says that hallucinogenic drugs were formative in his exploration of physics. ‘Not in the sense that you take acid and see new physics, or new interpretations of quantum mechanics, of course. But rather that psychedelic drugs have a powerful way of telling us, look, your common way of seeing reality is not so solid after all: reality can actually be perceived in quite alternative manners. Common sense can be dramatically misleading when trying to understand Nature beyond the everyday regimes in which we live.’
Rovelli’s intellectual breadth is apparent in Helgoland. Among his stated influences are Nāgārjuna, a second-century Buddhist philosopher who posited that ‘nothing exists in itself, independent of [anything] else’, and Alexander Bogdanov, a Marxist thinker who proposed a departure from 19th-century materialism — all in a book about quantum mechanics. The latter part of Helgoland even touches on the problem of consciousness, suggesting that a new interpretation of quantum mechanics might hold a key to understanding how consciousness arises from inanimate matter.
With characteristic humility, he notes that his intellectual fluidity is ‘unusual, but not unique’: ‘I know scientists with curiosity and interests larger than mine.’ He says ‘many biologists acknowledge Erwin Schrödinger’s influence as absolutely crucial’, referring to the early quantum physicist’s book What is Life?, which used physical principles to predict the existence of genetic code nine years before James Watson and Francis Crick’s discovery (both scientists acknowledged Schrödinger’s influence). ‘Einstein was immersed in philosophy: he read Hume and Kant and Schopenhauer and Mach in detail, and he used those ideas ... You find those ideas in general relativity.’ As he writes in Helgoland, ‘Philosophers offer original ways of rethinking the world, and we can employ them if they turn out to be useful.’
The many influences in Rovelli’s work are not cosmetic; they are necessary to solve the problem at hand. He is a first-rate thinker precisely because of his dedication to his craft, spending ‘hours and hours, days and days, weeks and weeks, months and years on a single problem [loop quantum gravity]’. After all, distinctions between disciplines exist for a reason: ‘There is an … independence of levels of understanding of the world that justifies the autonomy of the different areas of knowledge,’ he tells us in Helgoland; ‘in this sense, elementary physics is much less useful than physicists would like to think … Knowing that my girlfriend obeys Maxwell’s equations will not help me to make her happy.’
‘There is a lot of push for interdisciplinary work in the universities nowadays … But it’s not sufficient to put two people with different disciplines in a room and say, now you collaborate.’ In fact, deepening a field of study can lead to unexpected intellectual fusion. ‘The 20th century has led to a lot of specialisation because fields have gotten a lot of knowledge and techniques, so it was natural that people focused on single things.’ Recalling an earlier mention of my biologist grandfather, Rovelli continues, ‘Your grandfather is probably not young anymore. And maybe when he started studying biology there was no biochemistry. It hadn’t been invented yet. Biochemistry has completely revolutionised biology. Suddenly, a lot of things that were strange and funny and incomprehensible are even more marvellous, because biochemistry is incredible. We see how it works. We’ve opened the machine and — wow, it’s fantastic!’ The vision is of islands of knowledge, borne apart on the continental drift of widening human understanding. The result is not of isolation, but genesis.
So, where does this leave our understanding of reality? How do Rovelli, Nāgārjuna and Bogdanov resolve Niels Bohr’s anthropocentric interpretation of quantum mechanics? ‘The key to the answer, I believe, is the simple observation that scientists … and their measuring instruments, are all a part of nature. What quantum theory describes, then, is the way in which one part of nature manifests itself to any other part of nature,’ Rovelli writes in Helgoland. ‘This is a radical leap. It is equivalent to saying that everything consists solely of the way in which it affects something else. When the electron does not interact with anything, it has no physical properties.’
Rovelli is not vainly clinging onto philosophical realism, as some philosophers of quantum mechanics have done: ‘I believe that we need to adapt our philosophy to our science, and not our science to our philosophy.’ Nor is he giving in to subjectivism, in which the world exists for our eyes only. ‘The life of an electron is not a line in space: it is a dotted manifestation of events, one here and another there.’ Interaction is the fundamental fabric of reality, not an intermediary gauze between “us” and “the world out there”. Interact with the electron twice — at the slits and at the screen — and you are examining a different reality than if you observe it only at the screen: of course your results would be different. However, the operative word here is “interact”, not “you”, as it has been in previous interpretations of quantum mechanics. The electron manifests itself to anything that interacts with it: to a rock, to another electron, to the dirt under your fingernails. Even not seeing the electron is testament to its passage through the other slit; as such, an interaction that constrains the electron’s path.
Rovelli, in pursuit of a solution to one of the 20th century’s enduring philosophical quandaries, is prepared to reject common sense, to enter into dialogue with thinkers separated by continents and millennia. He writes in his 2020 collection of essays: ‘New ideas do not fall from the sky. They are born from a deep immersion in contemporary knowledge … From endlessly turning over the open questions, trying all roads to a solution … until there, where we least expected it, we discover a gap, a fissure, a way through … a breach on to new territory.’ In the space between loop quantum gravity, ancient Buddhist thought and radical Marxist philosophy, Carlo Rovelli has founded an island of knowledge on which to rethink reality.
NIKITA OSTROVSKY reads Physics at Somerville College. If he fails his Part B exams for this interview, it will have been worth it.
Art by Agnes Halladay