It's the 5 of October 2021, at the end of incredible year for Italy, for better or for worse. It's not over yet though.

That day, in fact, the Swedish Royal Academy of Sciences hold the annual press conference for the announcement of the Noble Prize for physics, in Stockholm. Along with climate physicist Hasselmann and Manabe (a first for the field), the Academy gives half of the Nobel Prize 2021 to Italian physicist Giorgio Parisi [1][2]. The motivation isfor the discovery of the interplay of disorder and fluctuations in physical systems from atomic to planetary scales.

Giorgio Parisi was born in 1948 in Rome (Italy) and began his career in the Italian capital city, graduating in 1970 with a work about particle physics. Despite short periods spent in the United States and France, his life is in Rome, where he comes back in 1981 as professor of physics, in the University of Tor Vergata first and then at the La Sapienza University, where he's still working. His scientific interest goes from theoretical physics to probability theory. The work worth of the Noble Prize, however, is about "spin glasses" [3].

A spin glass is a crystalline structure containing magnetic atoms, arranged randomly. In particular, the “spin” [4] of each of these atoms tends to be discordant at any moment with respect to that of its neighbors. Individual spins therefore tend to change continuously, making spin glasses very messy and complex to study. Not by chance, they are defined as magnetically “frustrated”.

In the late 1970s, the replication method was used to catalog and try to predict the spin orientation in those glasses, according to some properties. However, there are infinite ways to arrange spin glasses, so different studies gave different results. Parisi found the way to make a hierarchy of spin glasses according to their similarity, considering the average state of the particles, and also finding an equation to describe the process [5][6][7]. Also thanks to this discovery, according to Parisi "words like chaotic, irregular, unpredictable, which in the past were seen as negative, now get a positive meaning” [8].

That theory has been applied to a wide range of problems (atomic structure, maths, biology, climate, …), all about complex systems. Scientific discoveries frequently have important applications in very distant fields. Parisi himself stressed the importance of basic research (in essence, the one not guided by any specific purpose) and has actively participated in campaigns on the importance of investing in public research [9]. It's important to stress his stances on many scientific and social issues, like the defense of the secular nature of the state and the criticism against biodynamic agriculture practices, up to the importance to fight climate change.

About the importance of understand and simplify complex problems, Parisi says in a recently published book [10] that "starting from being able to simplify physical phenomena to theiressence, mankind developed physics over the last centuries. And physics has become so powerful and rich that it can again introduce complexity and disorder into its models, what Galileo had been forced to exclude.

1 – Announcement of the 2021 Nobel Prize in Physics

2 – The 2021 Nobel Prize in Physics

3 –

4 – 0400. What is spin?

5 – Giorgio Parisi and the physics of complexity. Full movie HD

6 – What Giorgio Parisi discovered? | Nobel Prize in Physics 2021

7 – The spin glasses (and the technique of making people sit at the table)

8 – Parisi Giorgio

9 – Let's save the Italian research

10 – Giorgio Parisi, Also thanks to this discovery