EventHelge Kragh

Spin, Relativity and Quantum Mechanics

The new quantum theory of 1925-26 was non-relativistic and unable to explain the electron’s spin. And yet, a relativistic generalization of the Schrödinger equation, in the form of the Klein-Gordon equation, was known at an early date. In fact, Schrödinger originally started with the relativistic equation. However, it was only with Paul Dirac’s linear wave equation of 1928 that quantum mechanics and relativity theory appeared in a unified form. Not only did the Dirac equation account for the electron’ spin, it also led to the amazing prediction of the antielectron, and more generally antimatter. Dirac thought initially that the antielectron was identical to the proton and only later did he introduce it as a new elementary particle. The talk will survey the complicated route from the spectroscopic fine-structure (ca. 1895) to the discovery of the positron (1933), with a brief look to the later development. Some common misconceptions concerning this chapter in the history of quantum physics will be pointed out.

Lecture 1

About The Speaker

2012 Helge

Helge Kragh is presently Professor Emeritus at the Niels Bohr Institute in Copenhagen, and has previously held positions at Cornell University, University of Oslo, and University of Aarhus, Denmark. His work covers the history of physics, chemistry and astronomy since about 1800. He is a member of the Royal Danish Academy of Sciences and Letters, and the recipient of several international awards, including the Abraham Pais Prize for History of Physics awarded by the American Physical Society. His latest monograph, co-edited with M. Longair, is The Oxford Handbook of the History of Modern Cosmology (Oxford University Press, 2019).