Étienne Guyon

Superconductivity, superfluidity, liquid crystals, hydrodynamic instabilities and turbulence, porous media, granular systems and others are the themes on which the French physicist Étienne Guyon, who died on July 12 at the age of 88, made major contributions, widely recognized by the international scientific community.

But to mention only this essential aspect of his scientific life would be to neglect his personality, which is rare in this community. Étienne Guyon has distinguished himself as a teacher, writer, scientific animator, popularizer and institutional actor. As a professor at the University of Paris Orsay and the École Supérieure de Physique et Chimie Industrielles de Paris (ESPCI), he was also director of the Palais de la Découverte from 1988, a position he left in 1990 to take over the management of the École Normale Supérieure (ENS) until 2000, before returning as a researcher emeritus to the PMMH laboratory of the ESPCI, which he had created in 1978 and where he continued to work until his death.

In 1955, he passed the competition for the École Polytechnique and the ENS and chose the latter. In this year of the Algerian war, he was part of a group of Catholic students ("talas"), committed pacifists and active militants against the Algerian war. In 1961, he began an experimental thesis, which he defended in 1964, on superconductivity (electrical conduction without resistance at very low temperatures) with the young professor of physics at the University of Orsay Pierre Gilles de Gennes, of whom he was to be his first doctoral student and the faithful friend whom he accompanied in 1991 to Stockholm at the award ceremony of his Nobel Prize.

After his thesis, Étienne Guyon went to the University of California at Los Angeles to work on superfluid helium (flowing without viscosity at very low temperatures). Part of his experiments inspired the theory of Kosterlitz and Thouless, awarded in 2016 by the Nobel Prize in Physics.

Back at Orsay as a teacher, he joined a new activity initiated by Pierre Gilles de Gennes on liquid crystals. His work on the movement of liquid crystals subjected to temperature differences makes him an international reference in this field. Étienne Guyon then became one of the figureheads of the French research community on instabilities, chaos and turbulence, studies that would have a strong international impact between the 1980s and 1990s.

Then, in 1978, he joined the ESPCI to teach the physical hydrodynamics course, succeeding another great experimenter of turbulence and chaos, Pierre Bergé. He opened a new laboratory, which would later become the Laboratory of Physics and Mechanics of Heterogeneous Media (PMMH), today one of the largest at ESPCI. This Grande Ecole, attached to the City of Paris, trains engineers by favouring experimentation and research. It has a rich history in physics since Pierre and Marie Curie discovered radium there in 1898. It was, among others, directed by Paul Langevin, and when Étienne Guyon joined it, Pierre Gilles de Gennes assumed the direction.

The courses given at ESPCI by P. Bergé and E. Guyon have radically changed the traditional teaching of hydrodynamics. They provide it based on recent research results and make it the basis of an educational text of which Étienne Guyon was the co-author, under the title "Physical hydrodynamics". This book accompanies generations of students worldwide in their first steps in fluid mechanics.

At ESPCI, he developed research on hydrodynamic instabilities and porous media and opened a research activity on soft matter. Endowed with a remarkable capacity for work and a dazzling dynamism, Étienne Guyon was an enthusiastic scientific leader and played a crucial role in the genesis of a pioneering research style, combining physics and mechanics and inspired by statistical physics. He is interested in disordered matter and physical hydrodynamics. He founded the research group "Milieux Aléatoires Macroscopics" (MIAM), which structured, and still structures today, the French community of studies on soft matter.

His passion for research was also expressed through actions to popularize science in motion, explaining his work in simple words to share it, first, with his family and, more widely, with young people. In 1975, on the occasion of the National Congress of the French Physical Society, in Dijon, he was asked to install an open-air physics animation entitled Physique dans la rue, which was a great success. As he said himself, he was inspired by May 68 to create this science in the street.

He carried this experience with him when he chaired the orientation committee of La Villette when it opened and then at the Palais de la Découverte, which he directed from 1988. The model of the Palais de la Découverte (exhibitions, events, conferences), with ongoing relations with experiments and the world of research, suited this experimental physicist very well. During his short mandate, he revitalized the scientific clubs of young people, nicknamed -Les petits débrouillards- to which E. Guyon has always remained very attached. Very sensitive to the preservation of the Palais de la Découverte, which almost disappeared in the works of the neighbouring Grand Palais, he has recently actively campaigned for a revival of this establishment.

During his mandate as President of the French Physical Society, from 2002 and 2003, he was able to develop this vocation in the community of physicists in France. He completed his institutional experience in 1990 by directing the École Normale Supérieure for ten years. He thus crosses the 200 meters that separate the ESPCI from rue Vauquelin to rue d’Ulm to return to the places of his youth. During his mandates, he directed the commemoration of the bicentenary with numerous promotional operations for the ENS and the publication of various archival books.

His broad culture and sensitivity for the human sciences made him particularly attentive to literary students at the ENS. He notably intervened to develop IT in the literary departments and digitize the library. One of its most innovative initiatives was the creation of the "European" entrance examination allowing direct access to the normalien student category after an examination in one of the five authorized languages (English, German, French, Spanish and Italian). Currently, unfortunately, the international selection only gives access to scholarships.

Étienne Guyon energetically defended the precise use of the language in the world of science, even in the recurring debates in the laboratory during which he defended the use of French. This is how he was appointed expert to the General Commission of Terminology and Neology. By cultivating bilingualism, he promoted linguistic diversity. He liked to write, endowed with an easy and fast pen. A man of combat, he wielded the pen as a weapon and spoke easily to everyone. His voice carried far, literally and figuratively. Étienne Guyon was, in his last years, a prolific author writing, in an original style, a dozen books of scientific popularization in which he exposed, in simple and accessible language, the latest results of the physics of disorder straight out of the laboratories. Many of its co-authors were young scientists marked by this exercise of working together.

He closely supported his wife, Marie-Yvonne, who was very committed to solidarity actions, himself giving literacy lessons to undocumented immigrants or getting involved in projects in Mali. His family home in Limours was open to anyone who needed a roof. He, who had suffered the pain of losing two of his four children, radiated with pleasure years later announcing, urbi et orbi, the coming into the world of a 9th great-grandchild.

José Eduardo Wesfreid ; Directeur de Recherche au CNRS (PMMH-ESPCI)

Link to the obituary published in "Le Monde"