“The first amazing fact about gravitation is that the ratio of inertial mass to gravitational mass is constant wherever we have checked it. The second amazing thing about gravitation is how weak it is.” -Richard Feynman
One of the strangest, most novel predictions of Einstein’s relativity is that mass would not only curve space, but that the curved space would act like a lens. Background light traveling past this mass would become magnified, distorted and stretched. In some cases, arc, multiple images or even perfect, 360º rings would occur.
Although this gravitational lensing phenomenon was theoretically predicted shortly after it was proposed, it was only in 1937 that Fritz Zwicky realized that a galaxy cluster could cause this phenomenon. 42 years later, 1979’s discovery of the Twin QSO validated this picture, and hundreds of other instances of lensing have been found since.