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*A Personal Historical View of the Theory of Deterministic Chaos *

## David Ruelle

(Member of the Académie des Sciences de Paris; foreign member of the American Academy of Arts and Sciences and of the US Academy of Sciences)

**Tuesday, April 5, 2022, @5:00pmJefferson Lab 250**

**and streamed live via Zoom:**

https://harvard.zoom.us/j/97699458611?pwd=dEpYQ1VEZUtUeWdQWjQzbDMvTG1Odz09

Passcode: 086979

Classical deterministic time evolutions exist with apparent random features, as is seen in hydrodynamic turbulence. Such phenomena have been called deterministic chaos, and are associated with sensitive dependence on initial conditions. We discuss chaos theory with emphasis on the multidisciplinary work concerning chaos in natural phenomena during the three decades 1970-2000. Work in that period has involved developments in pure mathematics, new experimental techniques, and the use of digital computers. The problems addressed include hydrodynamical turbulence, meteorology, chemical kinetics, and the astronomy of the solar system. These problems can be handled with precision. More general applications of deterministic chaos theory remain open.

______________________________________________________________________**David Ruelle** (b. 1935) is a mathematical physicist who worked at The Université libre de Bruxelles (Belgium), ETHZ (Eidgenössische Technische Hochschule Zürich, Switzerland), The Institute for Advanced Study (Princeton), and Institut des Hautes Etudes Scientifiques (France). His research spanned quantum field theory (more specifically, the Haag-Ruelle scattering theory), equilibrium statistical mechanics (thermodynamic limit and the Dobrushin-Lanford-Ruelle equation), the latter resulting in two books: *Statistical Mechanics Rigorous Results *(1969) and *Thermodynamic Formalism* (1978), as well as hyperbolic dynamics (transfer operators, dynamical zeta functions, Sinai-Bowen-Ruelle measures). Ruelle was interested in hydrodynamic turbulence, and is one of the fathers of chaos theory (see Ruelle-Takens (1971), etc.). He has made a number of other scientific contributions and his current interests center on nonequilibrium statistical mechanics.

David Ruelle has also written two books for general audience: *Chance and Chaos *(1991) and *The Mathematician's Brain* (2007). He is now Honorary Professor of Mathematical Physics at the The Institut des hautes études scientifiques (France).