My PhD Supervisor Just Won the Nobel Prize in Physics – Here’s How His Research on Complex Systems Changed Science

The Nobel Prize in Physics for 2021 has been jointly awarded to Italy’s Giorgio Paris, Japan’s Tsukuro Manebe and Germany’s Klaus Hasselmann for their “unprecedented contributions to our understanding of complex systems”.

When I heard this news, I could not believe it. I studied under Professor Paris at Sapienza University in Rome for my Master’s thesis and PhD in Theoretical Physics.

Don’t get me wrong when I say I was in disbelief. Of all the people I have met in my research experience – perhaps in my life – he is undoubtedly the simplest. So I was not surprised about the decision of the Nobel Prize Committee to nominate him as a laureate. Rather, it was his decision to recognize his “contribution to our understanding of complex systems” that piqued my interest.

The award for Professor Paris, split with trail-blazing meteorologists Professor Manabe and Professor Hasselman, is a wonderful recognition of an entire research field – perhaps a little less glamorous than the likes of general relativity or string theory – that seeks to understand and model. tries to do what we call “complex systems” in physics.

These include things like the climate ecosystem, the financial system, and biological phenomena, to name a few. The variety of complex systems – represented by fluctuating markets and stars in the swarm – makes it very difficult for them to achieve any sort of universal rule. Paris’ work has allowed us to draw unprecedented conclusions about systems that, on the surface, appear random, unpredictable and impossible to model theoretically.

Unlike some other physics models, complex systems are not a collection of identical particles interacting regularly in a way that is consistent and predictable. Instead, complex systems are systems of elements that, potentially different from each other, interact in different and seemingly unpredictable ways when exposed to varying external conditions.

A stepping stone to the modeling of complex systems is the theory of “disordered systems”. These are essentially systems in which different pairs of elements experience different, potentially conflicting forces that can “frustrate” the elements.

One way to illustrate this is to imagine a party (a closed social system), where Alice wants to chat with Bob, and Bob wants to chat with Charlie, but Charlie doesn’t want to chat with Alice. Here’s to despair – so what should they do?

Professor Parsi’s research explained what happens when frustration occurs in disorganized and complex systems. They recognized that complex systems are able to remember their trajectories over time, and can remain trapped in sub-optimal states for long periods of time.

In the example of our party, imagine that Alice, Bob, Charlie and other guests are randomly switching conversation groups and partners, hoping to find the best group of people to chat – yet Possibly will never be able to find it. That sub-optimal state can get stuck in a complex system.

pattern from disorder

One of the many theoretical tools that Professor Parisi has used to establish his theory is the so-called “replication trick” – a mathematical method that takes a disordered system, repeats it several times, and compares that How do the different replicas of System. You can do this, for example, by compressing the marbles in a box, which will create a different configuration each time you compress. Over many repetitions, Paris knew, could tell the pattern.

This method is now one of the few theoretical pillars for the development of the whole theory of complex systems as we know it today. Professor Paris’s theory makes reliable predictions on the statistical properties of complex systems ranging from supercooled liquids (liquids below their freezing temperature), frozen liquids, amorphous solids such as glass, and even clumps of stars. Shown to give.

The theory of disordered systems allows us to make sense of the beautiful emergence of coherent flight patterns within tight flocks of birds—which manage to coexist and form vast groups despite adversity.

The same framework has been used to make sense of the Earth’s climate. The meteorologist sharing the Nobel Prize with Professor Paris will rely on breakthroughs in theoretical physics to produce the models we now use to reliably demonstrate global warming.

Read more: Nobel Prize: Why climate modelers deserved a physics prize – they’ve been proven right time and time again

I had the opportunity to discuss these topics with Professor Parisi in Rome while conducting his experiments with flocks of birds and during his computer simulations on the behavior of glass. It is not at all surprising to me to learn a little bit of his mind that he has been awarded the Nobel Prize in Physics.

But I am pleasantly surprised that the field of complex systems, which is quietly pushing the limits of theoretical research in physics, has been given this exposure. This Nobel Prize has provided new legitimacy – and, we can hope, new minds – to this fascinating area of ​​contemporary physics.