(Received February 10, 1949)
Electromagnetic interactions between matter can be described, for quantum-mechanical as well as for classical phenomena, as caused by a neutral vector-meson field, if the mass of the mesons is assumed to be so small as to be negligible.
One might perhaps think that such a description of an electromagnetic field would lead to difficulties with the derivation of Planck's radiation law, as this law depends essentially on the number of degrees of freedom of the field, which seems to be 3 instead of 2 for each plane wave in a meson field.
It is shown, however, that one can and should consider the longitudinal meson field in this case as a sum of a direct Coulomb field, which does not present a degree of freedom of the meson field, and a field of longitudinal “surplus”-mesons. True enough, the latter corresponds to a longitudinal degree of freedom in the meson field, but the coupling between these surplus-mesons and matter disappears in the limit of vanishing meson mass. The surplus-mesons therefore are not observable in this limit, moreover, they will not be emitted and are not in thermal equilibrium with the surrounding. Thence only the transverse mesons are to be taken into account in the derivation of a radiation law for mesons with vanishing mass, and Planck's law results.
URL : http://ptp.ipap.jp/link?PTP/4/165/
DOI : 10.1143/PTP.4.165