ResearchPod Summary
This paper investigates whether a massive moving object with charged internal degrees of freedom, such as a neutral atom, experiences a viscous force when interacting with a classical field at zero temperature in unbounded space. This phenomenon, termed vacuum viscosity, is theoretically linked to cosmological particle creation, the dynamical Casimir effect, and quantum friction. While previous studies focused on bi-partite systems like moving mirrors or spacetime boundaries, this work examines a tripartite system where internal electronic activities interact directly with a field, indirectly affecting the center-of-mass motion.
The authors employ a microphysics model known as the AMOF model, featuring three interlinked dynamical variables: the external mechanical degree of freedom, the internal harmonic oscillator degree of freedom, and an ambient massless scalar field. Initially, the authors perform a standard nonrelativistic calculation using lab time. This approach yields a damping or viscous force acting on the object's motion. However, a closer inspection of the Green function expansions reveals that assuming a fixed spatial separation during motion is fundamentally flawed.
To resolve the conflict, the authors formulate a fully relativistic covariant framework for both the scalar field and the internal degrees of freedom. By enforcing special relativity, the velocity-dependent viscous terms vanish from the equation of motion because internal energy is fully accounted for via mass-energy equivalence and mass renormalization. Consequently, Newton's first law holds true for an object in uniform motion, while Newton's second law requires a time-dependent relativistic mass rather than a vacuum viscous drag.
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