Forces from fluctuations in and out of equilibrium (in QED and active matter)
Mehran Kardar
Tue, Oct. 17th 2023, 11:00-12:00
Amphi Claude Bloch, Bât. 774, Orme des Merisiers

The pressure of a gas, the van der Waals attraction between molecules, and the Casimir force in quantum electrodynamic (QED) are common examples of forces resulting from equilibrium (thermal or quantum) fluctuations. Current research on “Active Matter” studies collective behaviors of large groups of self-driven entities (living or artificial), whose random motions superficially resemble thermally fluctuating particles. However, the absence of time reversal symmetry leads to unusual phenomena such as directed (ratchet) forces, and a pressure that depends on the shape and structure of the confining wall.  Some manifestations of QED fluctuations out of thermal equilibrium are well-known, as in the Stefan-Boltzmann laws of radiation pressure and heat transfer. These laws, however, acquire non-trivial twists in the near-field regime of sub-micron separations, and in the proximity of moving surfaces.  Symmetry arguments suggest that lateral ratchet forces should emerge out of equilibrium and with broken spatial symmetry. We inquire if such forces can be used to construct a heat engine, and discuss constraints on its operation.

Contact : Matthew VONHIPPEL


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