Violation of action--reaction and self-forces induced by nonequilibrium fluctuations

TL;DR

This paper demonstrates that nonequilibrium fluctuations in driven fluids can induce self-forces on asymmetric objects and violate the action-reaction principle, phenomena impossible at equilibrium, expanding understanding of fluctuation-induced forces.

Contribution

It introduces the concept that nonequilibrium conditions can lead to self-forces and action-reaction violations in Casimir-like forces, supported by explicit calculations in a reaction-diffusion model.

Findings

Self-forces can be induced on asymmetric objects in nonequilibrium fluids.

The action-reaction principle can be violated between objects in such conditions.

The sum of internal Casimir forces can produce a net self-force on combined objects.

Abstract

We show that the extension of Casimir-like forces to fluctuating fluids driven out of equilibrium can exhibit two interrelated phenomena forbidden at equilibrium: self-forces can be induced on single asymmetric objects and the action--reaction principle between two objects can be violated. These effects originate in asymmetric restrictions imposed by the objects' boundaries on the fluid's fluctuations. They are not ruled out by the second law of thermodynamics since the fluid is in a nonequilibrium state. Considering a simple reaction--diffusion model for the fluid, we explicitly calculate the self-force induced on a deformed circle. We also show that the action--reaction principle does not apply for the internal Casimir forces exerting between a circle and a plate. Their sum, instead of vanishing, provides the self-force on the circle-plate assembly.