On the occasion of the awarding of the Nobel Prize in Physics to the Italian Giorgio Parisi, professor at the Sapienza University of Rome, we spoke with Fèlix Ritort, professor of Physics at the University of Barcelona. Member of the Institute of Nanoscience and Nanotechnology of the UB (IN2UB), Ritort began his research in the 1990s under the supervision of the awardee, with whom he has signed more than twenty scientific articles.
"When I arrived at La Sapienza, he was already a professor", Ritort recalls. "I didn’t have an office and he offered me to share his, as if we were two students. He was a thesis supervisor who didn’t tell you whether you were doing well or badly: if I wasn’t doing enough, it was my problem", he adds. "He was a brilliant scientist, with great intuition and unconventional at all. He also had an extraordinary capacity for mental calculation: he was able to solve a cube root with decimals in a few seconds and without a calculator". Ritort spent six years working with Parisi, between 1989 and 1994, first on his doctoral thesis and then as a postdoc.
It was Javier Tejada, emeritus professor of the UB, who recommended Ritort to work with Parisi in Rome. In the late 1980s, Tejada was working experimentally with spin crystals and wanted a student to get theoretical training in the field. "At that time, spin crystals became fashionable. Interestingly, over the years they have had no practical application, but they have yielded a lot of intellectual results". Spin crystals are metal alloys in which atoms of other metals that behave like tiny magnets are mixed (these are called spins). These impurities cause a "magnetic frustration" that causes the metal atoms to point randomly in different directions.
Parisi, in the 1980s, had discovered hidden spin organization patterns in these systems and developed a theory of disordered and random phenomena that could be applied to other complex systems: replica symmetry breaking (RSB). This theory, which would take thirty years to be mathematically proven, soon had many applications, from neural network to optimization theory in computer science. It was later applied to problems in biology such as protein folding or nucleic acids, a field of biophysics in which Ritort is currently doing research at the Small Biosystems Lab that he directs at the Faculty of Physics. More recently, Parisi explained the collective behavior of starlings, a paradigm of animal behavior in dynamic groupings.
About his apprenticeship with Parisi, Ritort explains that "experiments show you new realities that lead you to new discoveries, and Parisi taught me that theory too". "What you have to look for he continues is beauty, and his theory had it. Together with its vast applicability, it is one of the most revolutionary in modern physics, since it explains a new organization of matter".
According to Ritort, "Parisi has shown that disordered matter organizes itself spontaneously in many aspects of life similarly to a family tree". If we think, for example, of cell differentiation, in which a cell divides and at the same time each cell divides again, we have a temporary family tree. "I am convinced that, beyond its applications, Parisi’s discovery can be linked to the origins of life. I believe that in the coming decades science will discover that living matter is organized in this pattern and that it is a spontaneous manifestation of this discovery", says the researcher.
In a paper published in the journal of the European Physical Society, Ritort recalls that the evidence for Parisi’s theory remains controversial from an experimental point of view: "In theoretical physics, many important discoveries have had to wait decades until they have been experimentally proved (e.g., gravity, gravitational waves or black holes), and RSB may be no different", he predicts.