An ode to complexity

In 2021, Giorgio Parisi was awarded the Nobel Prize in Physics for the discovery of the interplay of disorder and fluctuations in physical systems from atomic to planetary scales. He shared the prize with Syukuro Manabe and Klaus Hasselmann, who earned it for the physical modelling of Earth's climate, quantifying variability, and reliably predicting global warming.

This was, arguably, the first award of a Nobel Prize in the area of complexity. In its citation, the Nobel Foundation started by asserting, "Our world is full of complex systems characterised by randomness and disorder", and then adding (for Manabe and Hasselmann), "One complex system of vital importance to humankind is Earth's climate". For Parisi, it said, "... Giorgio Parisi discovered hidden patterns in disordered complex materials. His discoveries are among the most important contributions to the theory of complex systems."

Given that nonlinear science, complexity, disorder, and order have all been areas of my own research interest, I am biased, to be sure, but this is a book that is well worth the read. Parisi is one of the world's most influential (and cerebral) statistical physicists, and the Nobel comes at the tail of a long list of honours, of which there will likely be more. The different areas that bear his imprimatur are many: the KPZ equation (for Kardar-Parisi-Zhang) in the study of aggregation, the Altarelli-Parisi equations in particle physics, the introduction of the multifractal formalism in turbulence, spin glasses, or the quantitative research of the murmuration of starlings (which feature in the title of the book and its cover).

This set of essays in In a Flight of Starlings conveys the essence of Parisi's discoveries to the general reader, for the most part, quite successfully. The chapters, each of them fairly short, fall into three categories. The general theme of complexity in physical systems, namely order and disorder in nature — phase transitions, emergence, spin glasses, and flocking behaviour — is discussed in a few. Some personal history on what it was like to be working on physics in Italy in the 1960s and 1970s is shared in a couple of chapters; in some others, Parisi shares his rumination on the nature of creativity, on metaphors in science, and a final word on the meaning of it all — why we do science in the first place. (Spoiler alert: we do it for fun! Parisi quotes Richard Feynman, "Science is like sex: sometimes something useful comes out, but that is not the reason we are doing it.")

Reading a formal scientific paper by Parisi has never been very easy — there are tools and techniques that he pulls out of unfamiliar hats — but it has often been rewarding. This book is probably the only one that Parisi has written for a lay audience and is based in part on a set of interviews with science communicator Anna Parisi (who is not related to him). First published in Italian in 2021 as In un volo di storni, the book was translated by Simon Carnell, and has an easy conversational style, keeping the frank matter-of-factness of Parisi as he describes how he developed ideas, partly by analogy, partly by metaphor, but mostly by hard work and application.

Parisi's manner is very direct. He describes the problems that interest him scientifically without exaggerating their importance or dumbing down the language. For instance, the murmuration of starlings is a captivating sight, but there are deep questions that this phenomenon poses, such as: is there a leader or is the behaviour self-organised; how is information transmitted through the flock; and so on. As he describes the work that he and his group carried out, one has a sense of the process of discovery, of what it takes to study such phenomena, and enough detail is shared to make one also feel like a participant and not just a bystander.

The same goes for the chapters on phase transitions and spin glasses. The problems are articulated clearly, the history of the area is described in sufficient detail, and the explanations come with a number of diagrams but no equations (keeping Stephen Hawking's warning in mind, no doubt, that for every equation, his readership would halve!). The basic ideas of the replica trick or scale invariance are conveyed in simple language, and without obfuscation.

Although this works admirably in making the physics of complex systems understandable, one might argue that the more valuable part of the book is the more reflective and analytical set of essays on the value of doing science. These essays were written prior to 2021, and it is clear that Parisi has long occupied an important and influential position as a public intellectual and as a voice for Italian science.

Parisi was elected to the American Philosophical Society in 2013, and that seems entirely fitting for a person who has done much to reveal the commonality between diverse areas in physics (or nature), namely the idea of universality. He also speaks unselfconsciously about the powerful role of incubation and intuition in scientific discovery, about the role of the subconscious and "nonverbal" thinking. Some of these ideas are presented in an exploratory and tentative manner, but this only makes the ideas more approachable and adds to the charm.

Science advocacy is another running theme through the essays. Starting off, Parisi makes his position clear, that it is "essential that the public have a fundamental understanding" of the practice of science. "Our generation is on a road fraught with dangers. It is as if we were driving at night: the sciences are our headlights, but it is the responsibility of the driver to not leave the road and to take into account that the headlights have a limited range."

Understanding the limitations of the sciences is as important as (or maybe even more than) believing in the worth of science: Parisi is an articulate and honest spokesperson for best practices in this domain. "Science needs to be defended not just for its practical aspects but for its cultural value," he says in the final pages, emphasising a point that is all too often ignored: it is not just for its significant contribution to making life better or in facilitating technological advances, but because it is integral to our modernity.

"We need to promote initiatives," he writes in conclusion, "that allow people to approach modern science. If we don't do this, scientists themselves will not be able to escape responsibility for the consequences."

This simple credo should become an integral part of the manifesto of the modern scientific enterprise: when scientists do not make an effort to communicate candidly about what they do, it is a disservice to society, directly or indirectly reducing public trust in science. Parisi's book succeeds spectacularly in giving the lay reader a starling's-eye view of the science of complexity and making it very approachable.

Dr Ram Ramaswamy holds the D.D. Kosambi Chair in Interdisciplinary Studies at the University of Goa. His research interests include chaos and nonlinear dynamics.