Abstract
A hundred years ago, two British expeditions measured the deflection of starlight by the Sun’s gravitational field, confirming the prediction made by Einstein’s General Theory of Relativity. One hundred years later many physicists around the world are involved in studying the consequences and use as a research tool, of the deflection of light by gravitational fields, a discipline that today receives the generic name of Gravitational Lensing. The present review aims to commemorate the centenary of Einstein’s Eclipse expeditions by presenting a historical perspective of the development and milestones on gravitational light bending, covering from early XIX century speculations, to its current use as an important research tool in astronomy and cosmology.
Highlights
On the 6th of November of 1919 the results of two British expeditions to observe a solar eclipse that took place on May 29th of that same year, were released at a joint meeting of the Royal Society and the Royal Astronomical Society
The conclusion given at that meeting was: “the results of the expeditions to Sobral and Principe can leave little doubt that a deflection of light takes place in the neighborhood of the Sun and that it is of the amount demanded by Einstein’s generalized theory of relativity, as attributable to the Sun’s gravitational field” [1]
To commemorate the centennial of Eddington’s and colleagues’ key observation that tested Einstein’s theory, shaking our conceptions of space and time, we present a historical review of several phenomena collectively known as gravitational lensing effects, that have their roots in those observations made in 1919
Summary
On the 6th of November of 1919 the results of two British expeditions to observe a solar eclipse that took place on May 29th of that same year, were released at a joint meeting of the Royal Society and the Royal Astronomical Society. Universe 2020, 6, 9 the gravitational field of the interposed object acts like a lens, focusing the light and producing effects such as: magnification of sources, image distortions, replicating images of a single source or shifting the apparent location of the source These four consequences of gravitational light deflection are collectively known as gravitational lensing effects or lensing for short. The interest in gravitational bending of light originates in early speculations on the existence of massive stellar objects (“dark stars”) capable of modifying trajectories of light rays This led, at that time, the need to value the mass of stars and the development of means to do so, such as the torsion balance. At this point we will abandon our chronological storyline to follow the narrative into several topics in separate sections, covering the relevance of lensing in astronomical observations and its cosmological implications
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