Giorgio Parisi - In A Flight Of Starlings (Allan Lane, 2023) ****

Giorgio Parisi won the Nobel Prize in Physics in 2021 for his “discovery of the interplay of disorder and fluctuations in physical systems from atomic to planetary scales.”

In this short book he describes, explains and muses on complex systems, such as the flight of starlings, which is only the subject of the first chapter. His writing is simple, elegant and accessible, and easy to understand for the lay reader. 

He explains how as a young researcher he was encouraged to focus on just a few subjects instead of "concentrating on a few important ones. On the one hand this was obviously good advice, but on the other it was precisely by studying many things at once that I was able to make connections between different fields, the basis of many later discoveries"(p. 46). Next to starlings, we learn about the boiling of water and phase transitions, spin glasses, quantum physics, metaphors in physics and how ideas are born. Each chapter is worth reading, even if the first chapter on the flight of starlings was why I bought the book. The essence is about Parisi's work in complex system and the interaction of the various elements that they consist of. 

"In the context of physics, 'exchanging information' is equivalent to 'being subject to forces'. But generally speaking - given that the model can be applied to many fields of study, from physics and biology to economics and so on - there are many objects whose behavior depends on the behavior of other objects that are more or less in proximity to them, given that objects that are too far apart from each other cannot exchange information" (p. 47)

Not surprisingly, scientists from other disciplines are not always too happy when experts from other fields intrude in their area of interest. Just like anthropologists and sociologists hated the biologists who started with sociobiology, here the biologists are sometimes not all too happy when physicists come on their turf, when of course this cross-breeding is where the fun is. 

"We defined new standards of investigation in biology by using techniques originated and developed in statistical physics to solve complex and disordered problems. Not all biologists ap­preciated this incursion into their territory: some have shown themselves to be very interested in the results, while others have found our investigations to be too short on biology and top-heavy with math. The work was rejected by various journals that are probably kicking themselves now. After the great success of our first· article, which was cited in almost two thousand scientific publications, many others have followed." (p.17)

 And of course that's also where the value of analysing complex systems comes from. Understanding their workings at a very basic and abstract level, amplifies their use across contexts and areas of interest. 

"The actual world is disordered, and as we said at the start, many situations in the real world can be described as a large number of elementary agents that interact with each other. These interactions can be schematized with simple rules, but the results of their collective action are sometimes really unpredictable. The elementary agents can be spins, atoms or molecules, neurons, cells in general-but also websites, financial traders, stocks and shares, people, animals, components of ecosystems, and so on. 

Not all interactions between elementary agents generate dis­ordered systems. Disorder is born from the fact that certain ele­mentary entities behave differently from others: some spins try to go in opposite directions; certain atoms are different from most others; certain financial actors sell shares that others are buy,ing; some dinner guests actively dislike others who have been invited and want to sit as far away from them as possible. In all these disordered cases, the mathematical and conceptual tool I found is indispensable for tackling the problems associated with them." (p.80)

The book is an easy read, but with a very important topic.