Giorgio Parisi: A Nobel for complex systems

The last time an italian was awarded the Nobel Prize in physics was in 2002: Roberto Giacconi for his pioneering research in the field of X-ray radiation from the universe. Another italian research that probably could win the Prize was Adalberto Giazotto, who designed the VIRGO interferometer, that with LIGOs shared the first observation of gravitational waves. The Swedish Academy decided to assign the Prize to three of the LIGO's founders, Rainer Weiss, Barry Barish and Kip Thorne. But this is not a great problem: after all, the Nobel Prize serves to emphasize personal contributions, but also to establish key points in the knowledge, and in this sense, the role of Italy had already been indicated as fundamental.
Today, however, a long-awaited award arrives: Giorgio Parisi, theoretical physicist, whose works have provided important contributions to field theory and statistical physics, won the Nobel Prize in physics

for the discovery of the interplay of disorder and fluctuations in physical systems from atomic to planetary scales

During my PhD (we are talking about twenty years ago), there were two "mythical" italian theoretical physicists, Guido Altarelli and, in fact, Giorgio Parisi. The aura of myth of the pair was due to the then-known Altarelli-Parisi equation (later we discovered that the russian physicists Juri Lwowitsch Dokschizer, Vladimir Gribov and Lev Lipatov, more or less in the same years as the italians, had discovered a similar equation). The equation, which is "only" the fundamental one in quantum chromodynamics (the branch of physics that describes quarks, in short).
The physics of the Nobel Prize in Parisi, on the other hand, On the other hand, I explained the physics of Parisi's Nobel Prize on italian wikinews and I translate it here:
The Nobel Prize's research papers are published between 1979 and the early 1980s relating to spin glass, a particular metal alloy in which iron atoms are randomly mixed within, for example, a grid of copper atoms.
Due to the presence of the iron atoms, the material changes its magnetic properties. Each of the iron atoms behaves like a small magnet, influenced by the other nearby iron atoms. In a usual magnet all spins point in the same direction, but in a spin glass some pairs point in the same direction, others in the opposite direction. Parisi, in 1979, showed how the use of a particular mathematical technique, the replica trick, allowed to solve the spin glass problem.
In particular, the papers dedicated to spin glass can be found below:

Parisi, G. (1979). Infinite number of order parameters for spin-glasses. Physical Review Letters, 43(23), 1754. doi:10.1103/PhysRevLett.43.1754
Parisi, G. (1980). Magnetic properties of spin glasses in a new mean field theory. Journal of Physics A: Mathematical and General, 13(5), 1887. doi:10.1088/0305-4470/13/5/047
Parisi, G. (1983). Order parameter for spin-glasses. Physical Review Letters, 50(24), 1946. doi:10.1103/PhysRevLett.50.1946

In recent years, Parisi has been involved in climate change

Benzi, R., Parisi, G., Sutera, A., & Vulpiani, A. (1982). Stochastic resonance in climatic change. Tellus, 34(1), 10-16. doi:10.1111/j.2153-3490.1982.tb01787.x

a field that we can consider strictly connected with the study of complex systems.
This part takes us directly to the other half of the 2021 Prize, shared by Syukuro Manabe and Klaus Hasselmann precisely for their research on complex systems, which brings us straight to chaos theory. I hope to write soon some articles about this subject in the next weeks.
Stay tuned!