Bending space-time: a commentary on Dyson, Eddington and Davidson (1920) 'A determination of the deflection of light by the Sun's gravitational field'

Abstract

The famous eclipse expedition of 1919 to Sobral, Brazil, and the island of Principe, in the Gulf of Guinea, led by Dyson, Eddington and Davidson was a turning point in the history of relativity, not only because of its importance as a test of Einstein's General Theory of Relativity, but also because of the intense public interest which was aroused by the success of the expedition. The dramatic sequence of events which occurred is reviewed, as well as the long-term impact of its success. The gravitational bending of electromagnetic waves by massive bodies is a subject of the greatest importance for contemporary and future astronomy, astrophysics and cosmology. Examples of the potential impact of this key tool of modern observational astronomy are presented. This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society.

Keywords: Eddington; eclipse expedition 1919; general relativity; gravitational lensing; light bending by the Sun.

Figure 1.

The 16-inch lens and large coelostat (on the left) and the smaller 4-inch telescope in a square box (on the right), with its much smaller coelostat on location at Sobral, Brazil. (Courtesy of the Science Museum, London.)

Figure 2.

The radial deflections of the positions of seven stars observed by the 4-inch telescope at Sobral as a function of distance from the centre of the Sun. The scale on the abscissa is the inverse of the distance from the centre of the Sun. The dotted line shows the Newtonian prediction and the central heavy solid line shows the expectation of the General Theory of Relativity. The upper light solid line shows a best-fit to the deflection of the seven stars by the Sun. Image from [19] (Copyright The Royal Society).

Figure 3.

Measurement of the coefficient (1+γ)/2 from light deflection and time delay measurements [26]. In General Relativity, the value of γ is 1. The upper part of the diagram shows how the precision of the experiments has improved since the pioneering experiments of 1919. The lower part of the diagram shows the corresponding improvements in the limits to deviations from General Relativity from the Shapiro time delay experiments. (Courtesy of Prof. Clifford Will.)

Figure 4.

A Hubble Space Telescope image of the central region of the rich cluster of galaxies Abell 2218, showing the prominent arcs centred on the massive core of the cluster. The circular images are the gravitationally lensed images of a very distance background galaxy. The core of the cluster acts as a gravitational lens. (Courtesy of NASA, ESA and the Space Telescope Science Institute, Baltimore, MD, USA.)