# Michel Plancherel, une vie pour les mathématiques et pour le prochain

### Norbert Hungerbühler

ETH Zürich, Switzerland### Martine Schmutz

Université de Fribourg, Switzerland

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## Abstract

Michel Plancherel was one of the leading figures of Swiss mathematics of the 20th century. He is best known for his fundamental results in harmonic analysis and applications in PDE theory and the calculus of variations. A milestone in mathematical physics was his proof that mechanical systems cannot be ergodic. He also left his traces in algebra, in particular in the context of quadratic forms and the theory of commutative Hilbert algebras. Not less remarkable is Plancherel’s unfatiguing dedication to the community: He served as a president of the Swiss Mathematical Society, as vice-president of the International Congress of Mathematicians 1932 in Zurich, he was rector of ETH, president and co-founder of the foundation for the advancement of the mathematical sciences in Switzerland, and he served in many other institutions. He raised funds to help the 550 Hungarian students who escaped in 1956 to Switzerland, he was president of the Swiss Winterhilfe, an organization to help people during hard winters, and he presided the Mission Catholique Française in Zurich. With his wife Cécile, née Tercier, he had 9 children, five boys and four girls.