Classical-field theory of thermal radiation

TL;DR

This paper develops a classical field theory approach to thermal radiation, deriving Planck's law and Einstein coefficients without quantum mechanics, and shows the spectral energy density's dependence on atomic nature.

Contribution

It introduces a fully classical framework for thermal radiation, deriving key quantum results without quantization or photons, challenging traditional quantum interpretations.

Findings

Derives Planck's law within classical field theory.

Shows spectral energy density depends on atomic nature.

Validates Planck's law as an approximation at weak atomic excitation.

Abstract

In this paper, using the viewpoint that quantum mechanics can be constructed as a classical field theory without any quantization I build a fully classical theory of thermal radiation. Planck's law for the spectral energy density of thermal radiation and the Einstein A-coefficient for spontaneous emission are derived in the framework of classical field theory without using the concept of "photon". It is shown that the spectral energy density of thermal radiation is apparently not a universal function of frequency, as follows from the Planck's law, but depends weakly on the nature of atoms, while Planck's law is valid only as an approximation in the limit of weak excitation of atoms.