2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/158274We introduce the concept of Casimir friction, i.e. friction due to quantum fluctuations. In this first article we describe the calculation of a constant torque, arising from the scattering of quantum fluctuations, on a dielectric rotating in an electromagnetic vacuum.To appear in Modern Encyclopedia of Mathematical Physics (MEMPhys); campanion article to cond-mat/0503757; v2 - minor editorial changesQuantum Physicstext