The conceptual origins of gravitational lensing

摘要

We critically examine the evidence available of the early ideas on thebending of light due to a gravitational attraction, which led to the concept ofgravitational lenses, and attempt to present an undistorted historicalperspective. Contrary to a widespread but baseless claim, Newton was not theprecursor to the idea, and the first Query in his {\sl Opticks} is totallyunrelated to this phenomenon. We briefly review the roles of Voltaire, Marat,Cavendish, Soldner and Einstein in their attempts to quantify the gravitationaldeflection of light. The first, but unpublished, calculations of the lensingeffect produced by this deflection are found in Einstein's 1912 notebooks,where he derived the lensing equation and the formation of images in agravitational lens. The brief 1924 paper by Chwolson which presents, withoutcalculations, the formation of double images and rings by a gravitational lenspassed mostly unnoticed. The unjustly forgotten and true pioneer of the subjectis F. Link, who not only published the first detailed lensing calculations in1936, nine months prior to Einstein's famous paper in {\sl Science}, but alsoextended the theory to include the effects of finite-size sources and lenses,binary sources, and limb darkening that same year. Link correctly predictedthat the microlensing effect would be easier to observe in crowded fields or ingalaxies, as observations confirmed five decades later. The calculations madeby Link are far more detailed than those by Tikhov and Bogorodsky. We discussbriefly some papers of the early 1960s which marked the renaissance of thistheoretical subject prior to the first detection of a gravitational lens in1979, and we conclude with the unpublished chapter of Petrou's 1981 PhD thesisaddressing the microlensing of stars in the Magellanic clouds by dark objectsin the Galactic halo.