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“We are not entities, we are relations”, is a clever way for Carlo Rovelli to introduce himself. It’s a principle that has guided one of many strands of work that have made the physicist and author of best-selling books as Seven Brief Lessons on Physics, The Order of Time and his latest, Helgoland, one of the world’s most prominent public intellectuals.

Rovelli’s will be a familiar name to regular readers of New Ů��С��Ƶ – and rightly so, as for the past three decades he’s been the source of some of the most intriguing ideas in fundamental physics. They range across quantum physics, Einstein’s general relativity and the search for the holy grail of a theory that can combine these two theories, and which so mysteriously fail to gel.

Helgoland is all about Rovelli’s attempt to explain perhaps the biggest mystery within quantum physics – what the nature of a reality can be in which, as the theory suggests mathematically at least, things are undefined until we measure them. “Is the moon there when nobody looks?” is one way of expressing the obvious conundrum that arises from that, a quote often attributed to Albert Einstein. Rovelli asked a slightly different question in a feature article he wrote for us on the subject earlier in the year: does a chair exist by itself, if no one is sitting on it? His point is that any object is only defined by its relationship with other things. A chair might be called a chair because we sit on it. We might call it red because of a particular interaction between its wood, light scattering off it and receptors in our eyes. But that’s not saying any of those properties exist independently of those interactions.

In 1996, Rovelli began translating that insight to the quantum world, with an interpretation of quantum theory called relational quantum mechanics that’s since been expanded on by others. Its contention is that you can go some way to clearing up quantum mysteries by accepting there is no such thing as things, only relations between things. And so the same goes for us: we are not entities, we are relations. (If that basic idea intrigues you, I’d recommend the recent live talk Rovelli gave as part of our virtual events series in which he explores it in a little more detail.)

Do I buy that? Well, I’m not sure I do, but the point here is that no one has the answers – we are at the cutting edge of knowledge here, grappling to find a way forward at an interface where physics sometimes seems to dissolve into metaphysics.

That’s the context in which Rovelli has always shone, and it’s the one in which I first met him. In the summer 2019 – it seems a world away now – I was lucky enough to be invited to a conference hosted by the Foundational Questions Institute, FQXi, in the Tuscan hills. There, leading physicists and others chewed over what physics might contribute to two of the greatest mysteries of the human condition – the nature of our consciousness, our ability to have felt experience; and of our agency, our ability to make decisions freely that can affect the evolution of the universe around us.

I’ve always found myself impressed by Rovelli’s thoughtfulness, lucidity and also humility, with a readiness to admit what he doesn’t know and can’t know that can be rare among leading scientists. Those are the qualities that I see this video. I like the insights it gives into his rebellious past nature – something I was unaware about until I found it alluded to in his recent collection of essays, which comes with the mouthful of a title There Are Places in the World Where Rules Are Less Important Than Kindness – and how that makes for good science. Physics is about creating a picture of the world, and then changing it, as he says.

I hope you enjoy the short film, and it stimulates you to explore some of Rovelli’s other seminal ideas, many of them featured in and around New Ů��С��Ƶ. There’s his work on the mystery of why time flows, which you can read about in this feature or hear about in a talk he gave at our science festival, New Ů��С��Ƶ Live, in 2018. Or you might fancy reading about his work on white holes, inverses of those monsters of Einstein’s relativity, black holes, that constantly spew out matter. (You might also enjoy reading this essay on what happens to matter that falls into a black hole from There Are Places in the World Where Rules Are Less Important Than Kindness.)

The existence of white holes is as yet unproven, but is part of what is perhaps Rovelli’s biggest life work – his development of the theory of loop quantum gravity, a rival to string theory that seeks to unite quantum physics and general relativity and that was also the subject of his book Reality Isn’t What It Seems. You might like to see Rovelli as a white hole for ideas, so impressive and wide-ranging is his portfolio. Certainly, his is a voice that’s always worth listening to.