Articles | Volume 6, issue 1
Review article
05 May 2015
Review article |  | 05 May 2015

Expanding Earth and declining gravity: a chapter in the recent history of geophysics

H. Kragh

Abstract. Although speculative ideas of an expanding Earth can be found before World War II, it was only in the 1950s and 1960s that the theory attracted serious attention among a minority of earth scientists. While some of the proponents of the expanding Earth adopted an empiricist attitude by disregarding the physical cause of the assumed expansion, others argued that the cause, either fully or in part, was of cosmological origin. They referred to the possibility that the gravitational constant was slowly decreasing in time, as first suggested by P. Dirac in 1937. As a result of a stronger gravitation in the past, the ancient Earth would have been smaller than today. The gravitational argument for an expanding Earth was proposed by P. Jordan and L. Egyed in the 1950s and during the next 2 decades it was discussed by several physicists, astronomers and earth scientists. Among those who for a period felt attracted by "gravitational expansionism" were A. Holmes, J. Tuzo Wilson and F. Hoyle. The paper examines the idea of a varying gravitational constant and its impact on geophysics in the period from about 1955 to the mid-1970s.

Short summary
This paper discusses the hypothesis of the expanding Earth in the period ca. 1950-1975 and how it interacted with Paul Dirac’s cosmological hypothesis of a decreasing gravitational constant. It pays particular attention to the models in which the expansion of the Earth was thought to be caused by a varying gravitational constant. These models, primarily due to Pascual Jordan, László Egyed and Robert Dicke, were for a decade or so considered interesting alternatives to continental drift.