I. Abstract of The Quantum Theory of Radiation

Alexander S. Blum, Martin Jähnert

Abstract This paper studies the notion of virtuality in the Bohr-Kramers-Slater theory of 1924. We situate the virtual entities of BKS within the tradition of the correspondence principle and the radiation theory of the Bohr model. We show how, in this context, virtual oscillators emerged as classical substitute radiators and were used to describe the otherwise elusive quantum transitions. They played an effective role in the quantum theory of radiation while remaining categorically distinct and ontologically separated from the quantum world of the Bohr model. The notion of virtuality thus differs markedly from its counterpart in quantum mechanics or QFT.

Albert Einstein

Joseph H. Eberly

. It is pointed out that the self-consistent treatment of radiation reaction is a common feature of many Ph.D. theses of E. T. Jaynes' students and “grandstudents” in the 30-year period 1962 - 1992. In this way they are all descended from Microwave Laboratory Report 502, written by Jaynes at Stanford in 1958. A number of examples are described briefly, and a new example that extends the framework laid down in M. L. 502 is presented. Microwave Laboratory Report 502 In 1958 E. T. Jaynes wrote a paper entitled Some Aspects of Maser Theory that was issued as Microwave Laboratory Report No. 502 at Stanford University. The cover of the report is shown in Fig. 1. In the Abstract of M. L. 502 Jaynes identified the work as an examination of the relation between quantum electrodynamics and the semiclassical theory of radiation. M. L. 502 was intended to serve as a preliminary step in a study of the ultimate limitations on noise figure and frequency stability in molecular-beam masers. The Abstract says, among other things, that “the semiclassical theory, as extended here, is a far more reliable means of calculating radiation processes than usually supposed.” In the present author's view, M. L. 502 reported the first examination of dynamical questions that are now associated with the field of cavity quantum electrodynamics.

Albert Einstein

S. Brandt

Abstract There are two rather different phenomena that furthered the development of quantum theory: blackbody radiation and atomic spectra. In fact quantum theory began in 1900 with Planck’s radiation law and his introduction of the quantum of action h (Episode 7). His derivation of the law was by no means stringent. He assumed the existence of many resonators (atoms or molecules) of different but fixed frequencies ν, which could emit or absorb radiation only in quanta of energy E = hν. Einstein, in his light-quantum hypothesis of 1905, postulated that the energy quantization is a property of the radiation field itself and not due to the material resonators. He found a similarity between a cavity filled with radiation consisting of quanta and a vessel filled with gas consisting of atoms. However, he could not obtain Planck’s law but only Wien’s (Episode 10).

Peter Michler, Simone Luca Portalupi