T he multi-prize-winning theoretical physicist Giorgio Parisi was born in Rome in 1948. He studied physics at the Sapienza University in the city, and is now a professor of quantum theories there. A researcher of broad interests, Parisi is perhaps best known for his work on “spin glasses” or disordered magnetic states, contributing to the theory of complex systems.
For this work, together with Klaus Hasselmann and Syukuro Manabe, he won the Nobel prize in physics in 2021. His first popular science book, In a Flight of Starlings: The Wonder of Complex Systems , which charts some of the highlights of his life’s work and makes a passionate case for the value of science, is published on 11 July. How did you get interested in physics? As a young child, I was interested in numbers – my mother told me I learned to read numbers aged three.
On the street we’d be waiting for a tram and I’d say, here comes the number six. When it was time to go to university, I pondered if I should do physics or maths, but in the end I went for physics. Maybe because there were more popular books on physics than mathematics, which is so abstract that it’s difficult to describe.
What prompted you to write the book? The original idea was to describe how science is done. There’s a growing lack of trust in science, with people denying Covid, or the need for vaccinations, or climate change. In order to address this, it is very important to show how scientists do their work.
Your work can be fiendishly complex. Was it a challenge to write about it in an accessible way? Yes, it was. For me, it’s very important to use metaphorical language.
Sometimes, in popular science books, people write formulae. That would save a lot of time, but I would lose a lot of people because a formula that seems easy for me to read is harder for other people. So trying to describe some complex and sophisticated physics problem without formulae takes real effort.
You begin by writing about your study of starling murmurations, which seems an unusual subject for a physicist to tackle. Why was it worth exploring? We wanted to see if there were rules of interaction between starlings that account for their collective movements. This connected to attempts in physics to understand the behaviour of systems composed of a large number of interacting components.
In Rome in the winter, every evening we see starlings flocking above the trees, forming these amazing patterns. One of the problems was to understand the three-dimensional shape of the flock, which is impossible to capture from a single viewpoint. It was clear to us that this had to be done by physicists, because of the huge amount of data that had to be analysed.
The experiment sounds like a huge amount of work. It took a lot of time and effort. To create a 3D image, we positioned two cameras 25 metres apart on the roof of the Palazzo Massimo in Rome, to track each individual as they moved.
There were thousands of birds and we had to reconstruct the 3D position of each one. When you have two simultaneous images of a flock seen from a different angle, it’s not easy to match the bird in the first image with the same bird in the second. This was one of the major difficulties.
What were some of your findings? When the flock was turning, the impression that one has is that they are turning as a flock, but the reality is that some birds start to turn in advance and the others follow. We were able to get the acceleration of each bird and to see that some birds start to accelerate or turn in one direction and other birds follow and that this decision was propagating inside the flock. We also found that the flocks are flat like pancakes [rather than spherical].
That’s one reason why they can change shape so quickly. The flatter the object, the more it gives you an impression of change when it changes orientation. You also found that the flock was denser at the edges than in the centre.
This was completely unexpected. It’s a bit like what happens on crowded buses, where frequently the crush is greatest near the doors, where passengers who have just got on accumulate, together with those who are about to get off and others still who want to continue their journey. You are best known for your work on spin glasses.
What are spin glasses, first of all? There are hundreds of materials called spin glasses, but the typical ones are an alloy of gold with a small amount of iron. For physicists, spin means something magnetic, because magnetism is related to spin, to the fact that electrons turn around and work like small magnets. At high temperatures they behave like normal magnetic systems, but when the temperature falls below a certain value, they appear to behave like glass in that the magnetic changes get slower and it seems as if the system never reaches equilibrium.
Images produced by AI should have some kind of signature, to prevent us from losing contact with reality What are some of the real-world applications of this work? One direct descendant is artificial intelligence, in the sense that work on spin glasses has been very important for a lot of developments in studying neural networks in the 1980s and 90s, and neural networks are the basis of modern artificial intelligence. Do you have concerns about AI? Well, clearly it needs regulation. For example, images produced by AI should have some kind of signature so that people can understand if they are real or fake, to prevent us from losing contact with reality.
We had a meeting of academics at the G7 in Paris in 2019, and one thing that we were very worried about was weapons systems controlled by AI. Our viewpoint was that if one decides to kill some human being, that decision should be taken by people and not machines. You caused quite a stir in Italy recently when you claimed to have found a more energy efficient way to make pasta, by turning the heat off and putting the lid on two minutes after adding the pasta to boiling water.
That was a completely strange thing, because the idea was not mine. I saw a post on Facebook and I just shared it, thinking it was an interesting idea, but I never actually tried it. There were so many discussions about it, and it was amusing that everybody was saying that Parisi was saying this.
But maybe it works. I don’t expect there’s a big difference [between this and more conventional methods]. You’d have to do a blind experiment to test it.
How did it feel to win the Nobel prize? I was very happy but I didn’t have time to feel too much. I was busy running the Accademia dei Lincei , I had my work at the university, and the day after I had to do 20 interviews over Zoom and so on. So it took some time to be acquainted with it.
Has it changed your life or work in any way? Yes, a lot. Italy has a few Nobel laureates, but all of them live outside Italy apart from me. And therefore if for any reason whatsoever someone needs a comment from a Nobel laureate, they ask me.
In a Flight of Starlings: The Wonder of Complex Systems by Giorgio Parisi is published by Allen Lane (£20). To support the Guardian and Observer order your copy at guardianbookshop. com .
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From: theguardian
URL: https://www.theguardian.com/science/2023/jun/25/giorgio-parisi-nobel-prize-physics-spin-glasses-complex-systems-in-a-flight-of-starlings
