Forces Induced by Non-Equilibrium Fluctuations: The Soret-Casimir Effect

TL;DR

This paper extends the concept of fluctuation-induced forces to nonequilibrium systems, revealing a net force that causes objects to move toward colder regions and demonstrating violations of Newton's third law in certain configurations.

Contribution

It introduces a generalized framework for fluctuation-induced forces in nonequilibrium conditions, specifically analyzing the Soret-Casimir effect and its implications.

Findings

A net force pushes objects toward colder regions in a temperature gradient.

Casimir forces on two plates differ, violating Newton's third law.

Force behavior depends on nonequilibrium fluctuation conditions.

Abstract

The notion of fluctuation-induced forces is generalized to the cases where the fluctuations have nonequilibrium origin. It is shown that a net force is exerted on a single flat plate that restricts scale-free fluctuations of a scalar field in a temperature gradient. This force tends to push the object to the colder regions, which is a manifestation of thermophoresis or the Soret effect. In the classic two-plate geometry, it is shown that the Casimir forces exerted on the two plates differ from each other, and thus the Newton's third law is violated.