Brownian Motion in Robertson-Walker Space-Times from electromagnetic Vacuum Fluctuations

TL;DR

This paper studies how classical particles in a Robertson-Walker universe experience Brownian motion due to electromagnetic vacuum fluctuations, with motion characteristics depending on the universe's expansion.

Contribution

It demonstrates that electromagnetic vacuum fluctuations cause Brownian motion in particles within an expanding universe, considering various couplings and scale factors.

Findings

Particles exhibit non-zero mean squared velocities.

Brownian motion depends on the universe's scale factor.

Different couplings and models influence the motion characteristics.

Abstract

We consider classical particles coupled to the quantized electromagnetic field in the background of a spatially flat Robertson-Walker universe. We find that these particles typically undergo Brownian motion and acquire a non-zero mean squared velocity which depends upon the scale factor of the universe. This Brownian motion can be interpreted as due to non-cancellation of anti-correlated vacuum fluctuations in the time dependent background space-time. We consider several types of coupling to the electromagnetic field, including particles with net electric charge, a magnetic dipole moment, and electric polarizability. We also investigate several different model scale factors.