Comment on "Temperature dependence of the Casimir force for lossy bulk media"

TL;DR

This paper refutes a recent claim that Lifshitz theory is invalid for thermal Casimir force calculations in finite-sized bodies, showing that dominant evanescent waves are well within the size limits of experimental setups.

Contribution

The authors clarify the role of evanescent waves in thermal Casimir force calculations, correcting misconceptions about the applicability of Lifshitz theory with the Drude model.

Findings

Evanescent waves dominate thermal corrections in Casimir force.

Wavelengths of relevant evanescent waves are smaller than test body sizes.

Misinterpretation arose from confusing propagating and evanescent waves.

Abstract

Recently Yampol'skii et al. [Phys. Rev. A v.82, 032511 (2010)] advocated that Lifshitz theory is not applicable when the characteristic wavelength of the fluctuating electromagnetic field, responsible for the thermal correction to the Casimir force, is larger than the size of the metal test bodies. It was claimed that this is the case in experiments which exclude Lifshitz theory combined with the Drude model. We calculate the wavelengths of the evanescent waves giving the dominant contribution to the thermal correction and we find that they are much smaller than the sizes of the test bodies. The opposite conclusion obtained by the authors arose from a confusion between propagating and evanescent waves.