The BKS Theory and the Light-Quantum Hypothesis: Virtual Entities and Transitions to Intermediate States, But in Different Conceptual Frameworks (1923–1925)
Markus Ehberger
Abstract Prior to the development of matrix and wave mechanics, virtual entities figured prominently in the so-called BKS theory. According to some historians, the virtual oscillators of the BKS theory and their mathematical representations are directly connected to the concepts of virtual transitions/states. I will analyse the meaning of the term “virtual” in BKS, discuss the theory’s most important conceptual building blocks and its impact on dispersion theoretic accounts, most importantly the Kramers-Heisenberg paper of 1925. Then I will turn to a development that has nearly faded from sight: Shortly before the development of quantum mechanics, but from a light quantum point of view, physicists developed the idea that scattering and dispersion is composed of successive emission and absorption processes through “intermediate states”. The discussion of both of these strands, BKS and the light-quantum viewpoint, will serve as basis for the further development and for an important question to be answered in the following: Was there a generative connection between virtual oscillators and what came to be known as virtual transitions?
Science networks•Jan 1, 2026•1 citation