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The European Physical Journal H

Charles Galton Darwin’s 1922 quantum theory of optical dispersion

Benjamin R. G. Johnson

Published May 28, 2020• 0 citations
Publisher

Abstract

Abstract The quantum theory of dispersion was an important conceptual advancement which led out of the crisis of the old quantum theory in the early 1920s and aided in the formulation of matrix mechanics in 1925. The theory of Charles Galton Darwin, often cited only for its reliance on the statistical conservation of energy, was a wave-based attempt to explain dispersion phenomena at a time between the theories of Ladenburg and Kramers. It contributed to future successes in quantum theory, such as the virtual oscillator, while revealing through its own shortcomings the limitations of the wave theory of light in the interaction of light and matter. After its publication, Darwin’s theory was widely discussed amongst his colleagues as the competing interpretation to Compton’s in X-ray scattering experiments. It also had a pronounced influence on John C. Slater, whose ideas formed the basis of the BKS theory.

DOI
10.1140/epjh/e2020-80058-7

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Failed attempts to understand the anomalous Zeeman effect contributed to the feeling of crisis that by 1924 characterized parts of the physics community. The solution proposed by W. Heisenberg’s ‘core model’ only raised other problems. Another indication was the state of radiation theory and the uncertain relationship between wave theory and the light quantum, a problem that resulted in the controversial BKS (Bohr–Kramers–Slater) theory of 1924. In the wake of this theory, H. Kramers and Heisenberg constructed a formal theory of dispersion that did not rely on electron orbits but only on observable quantities, in agreement with the ‘quantum mechanics’ programme of M. Born. The development culminated with Heisenberg’s paper of August 1925, which marks the end of the Bohr model and the beginning of quantum mechanics. The chapter reconsiders the crisis and the reasons for it, in particular the role of experimental anomalies.
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