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GP: Fachverband Geschichte der Physik

GP 11: The tools of physical theory

GP 11.4: Vortrag

Mittwoch, 20. März 2019, 15:30–16:00, HS 9

A History of Kirchhoff’s Law of Thermal Emission — •Pierre-Marie Robitaille¹ and Stephen Crothers² — ¹The Ohio State University, Columbus, OH — ²Tasmania, Australia

In 1859, Gustav Kirchhoff advanced his Law of Thermal Emission stating that within any arbitrary opaque cavity, in thermal equilibrium, the radiation will always be black, or normal, dependent only on temperature and frequency, while being independent of the nature of the wall. Kirchhoff’s proposed this law based solely on theoretical arguments and without experimental proof. Yet, since that time, no theoretical proof of Kirchhoff’s law has survived, as Hilbert highlighted at the beginning of the 20th century. Furthermore, this now includes the proof advanced by Max Planck himself [1]. At the same time, no experimental proof of Kirchhoff’s law exists. This is because, perfectly reflecting cavities are designed to be resonant. Quality factors for laser cavities have now achieved values of 10¹¹. Conversely, unlike rigid perfect reflectors, actual black bodies are able to do work, transforming any incident energy (either as photons or heat) into normal radiation manifesting the equilibrium temperature. Perfect reflectors can never achieve such a feat (unable to emit) and are in fact, completely uncoupled from the radiation field. In this talk, the history of black body radiation will be reviewed beginning with work preceding Kirchhoff until present. It will be demonstrated that Kirchhoff’s Law is indeed false and that universality does not exist. The consequences for modern physics will also be discussed. [1] P.-M. Robitaille and S. Crothers, Progress in Physics, v. 11, p.120-132, (2015).