DIRAC, P.A.M. (PAUL ADRIEN MAURICE). - THE RADIATION THEORY, THE BIRTH OF QUANTUM ELECTRODYNAMICS

The Quantum Theory of Emission and Absorption of Radiation. (+) The Quantum Theory of Dispersion. (2 Papers).

London, Harrison And Sons, Ltd., 1927. Royal8vo. Contemp. full cloth. A small stamp on verso of titlepage. In: "Proceedings of the Royal Society of London", Series A, Vol. 114. VI,IX,748 pp. (entire volume offered). Dirac's papers: pp. 243-265 a. pp. 710-728. Clean and fine.

First appearance of these milestone papers in Quantum Physics, constituting the first step in Quantum Field Theory and the invention of the Second Quantifization Method. By these papers Dirac "gave the foundation for that theory, quantum electrodynamics"(Pais).

"A New Radiation Theory. Dirac liked his transformation theory because it was the outcome of a planned line of research and not a fortuitous discovery. He forced his future investigations to fit it. The first results of this strategy were almost miraculous. First came his new radiation theory, in February 1927, which quantized for the first time James Clerk Maxwell’s radiation in interaction with atoms. Previous quantum-mechanical studies of radiation problems, except for Jordan’s unpopular attempt, retained purely classical fields. In late 1925 Jordan had applied Heisenberg’s rules of quantization to continuous free fields and obtained a light-quantum structure with the expected statistics (Bose Einstein) and dual fluctuation properties. Dirac further demonstrated that spontaneous emission and its characteristics—previously taken into account only by special postulates—followed from the interaction between atoms and the quantum field. Essential to this success was the fact that Dirac’s transformation theory eliminated from the interpretation of the quantum formalism every reference to classical emitted radiation, contrary to Heisenberg’s original point of view and also to Schrödinger’s concept of ? as a classical source of field.

This work was done during Dirac’s visit to Copenhagen in the winter of 1927. Presumably to please Bohr, who insisted on wave-particle duality and equality, Dirac opposed the "corpuscular point of view" to the quantized electromagnetic "wave point of view." He started with a set of massless Bose particles described by symmetric ? waves in configuration space. As he discovered by’ playing with the equations, ’ this description was equivalent to a quantized Schrödinger equation in the space of one particle; this’ second quantization’ was already known to Jordan, who during 1927 extended it into the basic modern quantum field representation of matter. Dirac limited his use of second quantization electromagnetic to radiation: to establish that the corpuscular point of view, once brought into this form, was equivalent to the wave point of view."(DSB).

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