Giorgio Parisi: the Nobel-prize winner whose complex interests stretch from spin glasses to starlings – Physics World

Giorgio Parisi: the Nobel-prize winner whose complex interests stretch from spin glasses to starlings – Physics World

Time Stamp: August 2, 2023 6:00 AM

Philip Ball reviews In a Flight of Starlings: the Wonder of Complex Systems by Giorgio Parisi (translated by Simon Carnell)

large flock of starlings
Universal insights Giorgio Parisi’s work centres on the fact that many complex systems – be they flocks of starlings or groups of magnetic atoms in a spin glass – share the same underlying physics. (Courtesy: iStock/AGD Beukhof)

When Giorgio Parisi was awarded the 2021 Nobel Prize for Physics alongside Klaus Hasselmann and Syukuro Manabe, news reporters faced a challenge. How the heck were they supposed to understand, let alone explain, what he had won it for? The issues tackled by Hasselmann and Manabe at least touched on a matter everyone recognized: climate change. But Parisi’s speciality – spin glasses and topological frustration – seemed as esoteric as it was baffling. So it was that, in some of the ensuing press conferences, Parisi found himself doing his best to field questions about climate, rather than his own work.

The author’s new book – In a Flight of Starlings: the Wonder of Complex Systems – might be seen as an attempt to redress that imbalance. In the space of just 120 pages, Parisi seeks to explain in lay terms just what it is that brought him such acclaim, which journalists covering his Nobel prize attempted to sweep under a rug modishly labelled “complexity”.

The book attains considerable charm and accessibility with its acute insights into the virtues and vicissitudes of doing science led purely by curiosity

Does he succeed? Not really, but don’t be put off. This slight volume might not be a paradigm of science communication, but it nonetheless attains considerable charm and accessibility with its acute insights into the virtues and vicissitudes of doing science led purely by curiosity.

I once saw Parisi deliver a plenary lecture at a statistical-physics meeting in Paris in the early 1990s, and I could not put that memory out of my mind as I read the gnarlier parts of this book. Throwing to the wind any idea that a plenary lecture should speak to a broad audience, Parisi’s talk condensed into a dense and deeply frustrated state, which he delivered, eyes half-closed, in a manner that conveyed simultaneously a touching faith in the knowledgeability of his audience and an ardent wish (or so it seemed to me) that scientific brilliance did not impose such obligations to take the stage. I’ve learnt that this experience of Parisi in action was not unusual.

I suspect that this book, composed in part of previously published essays, was encouraged by the publisher on the grounds that Nobel-prize winners become public figures with a duty to tell their stories. But it’s surely more than that. Parisi displays a genuine concern that scientists should strive to reach a broad audience. “For science to affirm itself as culture,” he writes, “we must make the public aware of what science is and how science and culture are intertwined, both in their historical development and in the practice of our time.”

Parisi, however, believes there is a “strong anti-scientific tendency” currently at work, complaining that “the prestige of science and popular trust in it is being rapidly undermined”. It’s a problem that is perhaps felt particularly keenly in Parisi’s native Italy, where I have often heard people lament the public’s low levels of understanding of – and interest in – science. This book was originally published in Italian in 2021 under the title In un Volo di Storni. Le Meraviglie dei Sistemi Complessi, and has been translated into English by Simon Carnell.

To his credit, Parisi does confess that scientists themselves sometimes “display an excessive, disingenuous confidence to a public that has a perception of the partiality and limits of their views”. Indeed, one of the attractions of his book is its frank discussion of how scientists arrive at ideas as much by intuition as by deduction, with the breakthrough moments often occurring during reverie or even sleep – albeit only after periods of intense but seemingly fruitless focus on the problem at hand.

In one telling anecdote, Parisi admits he could perhaps have won a Nobel earlier if only he’d been paying more attention. He and the Dutch theorist Gerard ’t Hooft should, he says, have seen in the early 1970s how to develop the quark–gluon theory of nucleons (quantum chromodynamics) using Murray Gell-Mann’s notion of “colour charge”. But they didn’t. The work was instead carried out a short while later by David Politzer, David Gross and Frank Wilczek, who bagged the Nobel Prize for Physics in 2004. Why didn’t Parisi see it, a friend later asked, given that he knew about all the ingredients? “It just didn’t occur to me,” he admits forlornly.

On the other hand, Parisi points out how sometimes it is enough for a scientist to know that a result, a proof or demonstration is possible, to enable them to find it for themselves. He describes how, for one particular colleague, “the simple information that [a certain] property was demonstrable was enough for him to arrive at the long sought-after proof for himself in less than 10 seconds”. Sometimes, he says, only “a minimal amount of information is enough to cause substantial progress in a field to which much thought has been given”. After all, frustrated systems don’t tend to evolve linearly.

Parisi’s admission that communicating science “is no easy task, especially with the hard sciences” is borne out by his text

This is all both valuable and fun. But Parisi’s admission that communicating science “is no easy task, especially with the hard sciences, where mathematics plays an essential role” is borne out by his text. Phase transitions, the frustration of spin glasses, and the trick of renormalization introduced by Leo Kadanoff and Ken Wilson are all presented clearly enough, but how Parisi made significant progress on tricky problems in these fields is harder to follow.

“It was technical, and as such difficult to explain in lay terms,” he confesses at one point, even admitting that a reviewer of his paper on that particular issue pronounced it “incomprehensible”. Indeed, it turns out that Parisi didn’t really understand the issue fully either, which illustrates another point about how ideas are born. Very often, one knows the right answer before being able to demonstrate or even to articulate why. The hard work is not finding the answer but finding the proof.

This notion is nicely illustrated by a story of a colleague who once posed Parisi a tricky question to which he immediately gave the answer. But when that colleague asked Parisi to explain his reasoning, he recalls: “At first I gave a completely nonsensical explanation, then a second that made a bit more sense, and only at the third attempt was I able to properly justify the right answer, which I had at first given for the wrong reasons.” It’s partly for such unveiling of the capricious scientific mind that this book can be enjoyed.

But perhaps most importantly, Parisi explains why reporters who were scratching their heads about how to explain spin glasses were missing the point of his research. His work isn’t about this system or that – a specific metal alloy, or the flocks of starlings in Rome that Parisi studied as a complex system in the 2000s. It’s about the universality of phenomena, whereby systems of many interacting components that look utterly different – be they flocks of starlings, groups of particles or the magnetic atoms in spin glasses – can be described using the same mathematics.

The fact that you can do so isn’t because there is a loose analogy between these systems but because they are all, at root, the same (collective) thing.

  • 2023 Penguin 144pp £20.00/$24.00hb
  • Find out more about the work of Giorgio Parisi in this video interview he gave for IOP Publishing:

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