Einstein Ring - History

History

The bending of light by a gravitational body was predicted by Einstein in 1912, a few years before the publication of General Relativity in 1916 (see Renn et al. 1997). The ring effect was first mentioned in academic literature by Orest Chwolson in 1924. Albert Einstein remarked upon this effect in 1936 in a paper prompted by a letter by a Czech engineer, R W Mandl, but stated

Of course, there is no hope of observing this phenomenon directly. First, we shall scarcely ever approach closely enough to such a central line. Second, the angle β will defy the resolving power of our instruments. —Science vol 84 p 506 1936

In this statement, β is the Einstein Radius currently denoted by (see above). However, Einstein was only considering the chance of observing Einstein rings produced by stars, which is low; however, the chance of observing those produced by larger lenses such as galaxies or black holes is higher since the angular size of an Einstein ring increases with the mass of the lens.