What theory did Bohr, Kramers and Slater advance in 1924?

Bohr, Kramers, and Slater advanced BKS theory in 1924. The name comes from Niels Bohr, Hendrik Kramers, and John C. Slater, who proposed a provocative account of how atoms interact with electromagnetic radiation.

BKS theory tried to preserve a classical wave description of light while retaining quantum transitions in atoms. It introduced “virtual oscillators” associated with possible absorption and emission frequencies. Most strikingly, it treated energy and momentum conservation as statistical rules applying overall, rather than necessarily holding in every individual interaction.

The proposal was partly motivated by Bohr’s resistance to Einstein’s light-quantum or photon hypothesis. It was not a lasting theory: coincidence experiments by Walther Bothe and Hans Geiger, along with work by Arthur Compton and Alfred W. Simon, showed that individual scattering events obeyed conservation laws in a way BKS could not explain.

Even though BKS failed experimentally, it helped stimulate discussion about quantum radiation and influenced the development of matrix mechanics. It is therefore remembered as both a historical dead end and an important step in quantum theory’s transition.