UNIVERSALITY IN GRAY-BODY RADIANCE - EXTENDING KIRCHHOFF LAW TO THE STATISTICS OF QUANTA

An ideal grey body is a macroscopic object with definite temperature w hich absorbs only a fraction of the radiation incident on it. Assuming that a grey body always emits in a mixed state, and that the radiatio n density matrix factors into matrices for the various frequency modes , we employ general arguments to derive the complete statistics of gre y-body radiance elicited by incident radiation. These depend only on t he temperature and the absorptivities for the various frequencies (hen ce are of universal form), and coincide with the statistics of black-h ole radiance first derived a decade and a half ago.