Introduction

Abstract

Nowadays, the behavior of light rays in a gravitational field must be described with Albert Einstein’s Theory of General Relativity. Long before the creation of this theory, however, it was suspected that gravity influences the behavior of light. Already in the first edition of his Opticks, published in 1704, Sir Isaac Newton formulated as the first Query: “Do not Bodies act upon Light at a distance, and by their action bend its Rays; and is not this action (caeteris paribus) strongest at the least distance?” It took almost three generations until this problem was carried further. In 1783, the British geologist and astronomer John Michell communicated in a letter to Henry Cavendish that “... if the semi-diameter of a sphere of the same density with the Sun were to exceed that of the Sun in the proportion of 500 to 1, a body falling from an infinite height towards it, would have acquired at its surface a greater velocity than that of light, and consequently, supposing light to be attracted by the same force in proportion to its vis inertiae, with other bodies, all light emitted from such body would be made to return towards it, by its own proper gravity” [MI84.1] . He even proposed how one might discover such “black” bodies, by observing companion stars revolving around these invisible objects.