The Nobel Prize in Physics 2021 has been awarded to Giorgio Parisi for his work in statistical physics, with the other half going to two specialists in climate modeling. Giorgio Parisi, professor at the University of Rome "La Sapienza", has made numerous stays in the Paris region, where he has established many collaborations.

Giorgio Parisi has been distinguished for his work on disordered systems: The Sherrington-Kirkpatrick model in the first place (a mean-field spin glass model), for which he found the solution "with a very unconventional method" and revealed a surprisingly complex and totally new physics. The Edwards-Anderson model then (a spin glass model on a lattice), with both analytical and numerical methods. Finally, the one-step replica symmetry breaking models, which have a very different physics and which, beyond their interest in understanding the physics of structural glasses, have opened a whole field of studies mixing physics and theoretical computer science (optimization problems, artificial intelligence, neural networks, ...).

Besides statistical physics, Giorgio Parisi is known for works on surprisingly varied subjects, such as field theory applied to particle physics (Altarelli-Parisi equations), critical phenomena (with an original method of calculating exponents), numerical simulations of lattice QCD (quantum chromodynamics), and even the mechanisms at work in starling clouds. The methods used range from mathematical physics to numerical simulations, including the design of computers dedicated to lattice QCD simulations.

He is a physicist full of ideas and he had many collaborations with IPhT physicists. He has co-authored 36 papers with our institute, first on mathematical physics and field theory (with R. Balian, E. Brézin, J.-M. Drouffe, C. Itzykson, A. Voros, J. Zinn-Justin, J.-B. Zuber), then on lattice QCD (A. Billoire), and these last years on the physics of disordered systems (A. Billoire, P. Urbani).