Perspectives on Quantum Friction, Self-Propulsion, and Self-Torque

TL;DR

This paper reviews nonequilibrium quantum forces and torques, including quantum friction and self-propulsion effects, highlighting their theoretical predictions and potential observability in thermal and vacuum environments.

Contribution

It provides a comprehensive overview of nonequilibrium fluctuational forces and torques, emphasizing phenomena beyond traditional Casimir effects and exploring conditions for self-propulsion and self-torque.

Findings

Quantum friction causes retarding forces on moving bodies.

Nonreciprocity can induce torques in stationary bodies out of thermal equilibrium.

Self-propulsion and self-torque can lead to observable terminal velocities.

Abstract

This paper provides an overview of the nonequilibrium fluctuational forces and torques acting on a body either in motion or at rest relative to another body or to the thermal vacuum blackbody radiation. We consider forces and torques beyond the usual static Casimir-Polder and Casimir forces and torques. For a moving body, a retarding force emerges, called quantum or Casimir friction, which in vacuum was first predicted by Einstein and Hopf in 1910. Nonreciprocity may allow a stationary body, out of thermal equilibrium with its environment, to experience a torque. Moreover, if a stationary reciprocal body is not in thermal equilibrium with the blackbody vacuum, a self-propulsive force or torque can appear, resulting in a potentially observable linear or angular terminal velocity, even after thermalization.