Nordström, Ehrenfest, and the Role of Dimensionality in Physics

Abstract.

In the summer of 1916, Finnish physicist Gunnar Nordström (1881–1923) arrived in Leiden to carry out research with Paul Ehrenfest (1880–1933), Hendrik A. Lorentz’s successor in the chair of theoretical physics. Nordström had recently published the first five-dimensional unified model of the universe, a theory that went virtually unnoticed by the physics community. Ehrenfest’s personal journals reveal that Nordström’s visit coincided with a flowering of Ehrenfest’s own interest in dimensionality, which resulted in his well-known paper on the connection between the fundamental laws of physics and the three-dimensionality of space. I examine Nordström’s and Ehrenfest’s collaboration and explore the relationship between their ideas and the Kaluza-Klein model of five-dimensional unification.