Force from Non-equilibrium Fluctuations in QED and Active Matter
Equilibrium fluctuation-induced forces are abundant in nature, ranging from quantum electrodynamic (QED) Casimir and van der Waals forces, to their thermal analogs in fluctuating soft matter. Manifestations of QED fluctuations out of thermal equilibrium are also 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. I will discuss dissipation in moving steady states, and the non-Gaussian fluctuations of a particle in a quantum bath.
Non-equilibrium fluctuation forces for particulate matter also hold surprises which I present in the contexts of diffusive transport, and active matter: For the simple case of a current of diffusive particles between parallel slabs, we find a force that falls off with slab separation d as kT/d (at temperature T, and in all spatial dimensions), but that can be attractive or repulsive. There is also a universal transient force when a system of particles undergoes temperature quench or sudden agitation. For a wide wide class of active systems, we find that the pressure exerted on a container depends on details of interactions with the confining walls, as well as wall curvature and asymmetry.
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