Comment on "Anomalies in electrostatic calibration for the measurement of the Casimir force in a sphere-plane geometry"

TL;DR

This paper critiques previous electrostatic calibration experiments measuring the Casimir force, proposing that surface imperfections and patch potentials explain observed anomalies rather than new physics.

Contribution

It introduces a model accounting for surface deviations and patch potentials, clarifying the anomalous electrostatic force behavior in sphere-plane measurements.

Findings

Surface imperfections affect electrostatic force measurements.

Patch surface potentials can cause deviations from Coulomb law.

The proposed model aligns with experimental observations.

Abstract

Recently W. J. Kim, M. Brown-Hayes, D. A. R. Dalvit, J. H. Brownell, and R. Onofrio [Phys. Rev. A, v.78, 036102(R) (2008)] performed electrostatic calibrations for a plane plate above a centimeter-size spherical lens at separations down to 20-30 nm and observed "anomalous behavior". It was found that the gradient of the electrostatic force does not depend on separation as predicted on the basis of a pure Coulombian contribution. Some hypotheses which could potentially explain the deviation from the expected behavior were considered, and qualitative arguments in favor of the influence of patch surface potentials were presented. We demonstrate that for the large lenses at separations of a few tens nanometers from the plate, the electrostatic force law used by the authors is not applicable due to possible deviations of the mechanically polished and ground lens surface from a perfect spherical shape. A model is proposed which explains the observed "anomalous behavior" using the standard Coulombian force.