Spectral and polarization characteristics of the nonspherically decaying radiation generated by polarization currents with superluminally rotating distribution patterns: comment.
I repeat my (very short and easy) disproof of the recurring main claim of Ardavan et al. [J. Opt. Soc. Am. A 21, 858 (2004)] that a smooth source of electromagnetic fields moving in a confined region can generate an intensity decaying more slowly than the inverse square of the distance away ("nonspherical" decay). The field is not isotropic, so energy conservation is not enough to dismiss the claim. Instead my disproof follows directly from Maxwell's equations, supplying an upper bound with inverse square decay on the intensity. It therefore applies under all circumstances, quite irrespective of any fast or slow motion of the source. Despite the falsity of the main claim, the derivation of the uniform approximation to the Green function for superluminal circulation, which was needed for the claim and is based on the previous work of the first author, is valid. Its validity, importantly, extends significantly beyond the regime envisaged by the authors, and it stands as a basic result of superluminal circulation.
Hannay
J H
JH
H. H. Wills Physics Laboratory, University of Bristol, UK. J.H.Hannay@bristol.ac.uk