THE OLD AND NEW QUANTUM THEORIES

L. H. Thomas

振一郎 朝永

Anthony Duncan A, Michel Janssen B

Abstract This chapter discusses how the new quantum theory took care of some of the failures of the old quantum theory and how it put the old theory’s successes on a firmer basis. Examples in the former category are the new theory’s resolution of the problems the old theory ran into with the anomalous Zeeman effect and helium (giving the wrong value for its ground state energy and being unable to explain the spectroscopic divide between ortho- and parahelium). Examples in the latter category are the fine structure in hydrogen and the Stark effect. The chapter also discusses some examples of Kuhn losses, instances where the new theory (at least initially) could not account for phenomena explained by the old one.

D. ter Haar, Arthur E. Ruark

Michela Massimi

The transition from the atomic core model to the electron's spin, the debate on the adequacy of semi-classical models, and the lack of an appropriate scientific terminology are symptomatic of the revolutionary transition from the old quantum theory to the new quantum theory around 1921–5. As such, they provide us with a foil for rethinking Kuhn's view on scientific revolutions. In this view, scientific revolutions are distinctively accompanied by incommensurability between paradigms, or – to use Kuhn's later terminology – untranslatability between scientific lexicons. In the light of the historical reconstruction offered in Chapter 2, I shall here argue for the prospective intelligibility of the revolutionary transition around 1924 via a two-step argument that (1) reconsiders Kuhn's notion of incommensurability as untranslatability (Section 3.2), and (2) offers a positive account of the way the electron's Zweideutigkeit and the exclusion rule came out of the old quantum theory (Section 3.3). The revolutionary transition from the old quantum theory to the new quantum theory On 5 November 1980, Thomas Kuhn delivered a lecture at Harvard University entitled ‘The crisis of the old quantum theory: 1922–25’. In his distinctive style of reasoning, Kuhn presented the rise of quantum mechanics after 1925 as the result of a period of crisis of the old quantum theory between 1922 and 1925. The old quantum theory – in Kuhn's view – cannot be regarded as a full-blown theory but rather as a set of algorithms to solve problems and paradoxes.