As for the third, I do know Giorgio Parisi's research in qualitative terms, and I happen to know him personally; well, at least we are Facebook friends, as maybe 500 of his contacts can also claim - plus, he once invited me to a symposium at the Accademia dei Lincei, of which he his vice-president. And I did write about his scientific accomplishments in the past here, on two occasions.
In the first case (2011) I briefly wrote about the awarding of the Max Planck medal to Parisi; in the second (2016) it was because of his win of the Onsager prize, for much the same reason of the Nobel prize he was awarded earlier this week. And I now realize I missed writing about his collection of the Wolf prize, too, which he won earlier this year. So, Parisi keeps us scribblers busy with the prizes he's taken a habit of collecting!
Indeed, the Nobel Prize to Parisi is a deserved recognition to his works on disordered complex systems and spin glass studies. Spin glasses are a very interesting system where a small amount of metallic atoms are frozen into random positions in a glass, and can have their spins aligned with those of other atoms or not. Depending on the relative alignments, the potential energy of the system is different. Any physical system tries to naturally roll down to the state of minimum energy, but in a spin glass things are not so easy, as there are a wealth of configurations and the way to the lowest energy state may be a tortuous path of unstable equilibrium states. Studying the behaviour of such systems, as well as related but completely different ones such as flocks of birds (birds in storm will adjust their motion to that of neighbors much like spins in a spin glass), is incredibly hard, and Parisi found the right ways to understand them.
Funnily, despite the enormity of the contributions he gave to condensed matter physics, to me and to many of my colleagues who study elementary particles rather than condensed matter systems (a bit of an antithesis!), Parisi is mainly one of the theorists behind a very important equation (rather, a set of equations) that describe the behaviour of quarks and gluons inside hadrons. In a nutshell, the probability to observe that a quark or a gluon inside a proton carry a certain fraction x of the parent's total momentum is a function of the energy at which one is probing the inside of the proton, and the Dogshitzer-Gribov-Lipatov-Altarelli-Parisi equations explain exactly how and why. Altarelli and Parisi, working together, found the rule independently to the Russian colleagues, and the equations now are identified by the acronym "DGLAP".
So, all the above is to say I cannot competently write about Parisi's work here. But I can tell you about the fact that he is a wonderful person and an elegant dancer! Jokes aside, this year the Nobel Committee did the right thing, in honouring one very special person and a great human mind. Cheers, Giorgio!
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Tommaso Dorigo (see his personal web page here) is an experimental particle physicist who works for the INFN and the University of Padova, and collaborates with the CMS experiment at the CERN LHC. He coordinates the MODE Collaboration, a group of physicists and computer scientists from eight institutions in Europe and the US who aim to enable end-to-end optimization of detector design with differentiable programming. Dorigo is an editor of the journals Reviews in Physics and Physics Open. In 2016 Dorigo published the book "Anomaly! Collider Physics and the Quest for New Phenomena at Fermilab", an insider view of the sociology of big particle physics experiments. You can get a copy of the book on Amazon, or contact him to get a free pdf copy if you have limited financial means.
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