Seminars & Colloquia Calendar

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Giovanni Gallavotti – University of Rome "La Sapienza"

Wednesday, September 23, 10:45AM

Title

“Viscosity, Reversibility, Statistical Ensembles for stationary non-equilibria”

New ideas generate misunderstandings and controversies. The theory of chaotic evolution has key implications on topics like nonequilibrium thermodynamics, ergodicity, entropy, turbulence, ensembles:
some of them will be presented to discuss novelties stemming out of Ruelle's and Bowen contributions and from the preceding work of Anosov, Sinai ... An example from the study of fluctuations in stationary states for
a simple Navier-Stokes system will be presented and centered on the question: is it possible that a viscous fluid could be described via reversible equations? A positive answer is proposed in analogy with the ensembles
equivalence in mechanics; the role of the container volume is played by a regularization parameter N for the equations, the temperature by the viscosity and the energy by the fluid enstrophy.  The thermodynamic limit will correspond to the removal of the regularization (N -> infinity). An interpretation of viscosity emerges which maintains the equation reversible while retaining the physical consequences of irreversibility, interpreted as a spontaneous symmetry breakdown. And typical fluctuation properties of reversible flows arise, in some cases, in the usual viscous flow.