Soldner’s 1801 paper on light bending by gravitational force

Few people could even imagine light can be bent by gravitational force. It took the unique genius of Einstein to achieve that. The story goes. But like many other legendary stories about prominent people, this story is also false. The idea of light bending by gravitational force was once pretty common.

Soldner, in 1801, calculated the bending of light when it passes through a gravitational field. The method is identical to the calculation of trajectory of any object passing through a gravitational field. He even calculated the condition when light cannot escape the gravitational pull. This is identical to the situation when planets, such as Earth, cannot escape the gravitational pull of the sun. In this way, he predicted the condition of blackhole.

The simplicity of his method is remarkable. Soldner is truly a great genius. However, “only sporadic and at times misleading references have been made to Johann Georg von Soldner”.

An introduction of Soldner’s life and work can be found from the following paper. In this paper, the history of ideas of light bending and variable speed of light is also discussed.

Jaki, S.L. (1978) Johann Georg von Soldner and the gravitational bending of light, with an English translation of his essay on it published in 1801. Found Phys 8, 927–950.

Some quotations from the paper.

To this technical conclusion, which in Lihotzky's eyes was damaging, though not fatally, to Einstein's theory, he added a philosophical conclusion which covertly endorsed the charge that relativity rested on complex assumptions bordering on contradictions. The truth of a theory, Lihotzky claimed, ultimately rested on its being free of contradictions: "if it makes a number of existing contradictions to disappear without introducing new ones then we must attribute to it a greater content of truth.  (P 931)

Comment: The logical inconsistency of the relativity theory is a big problem.

The other aspect is his rigorous insistence on the mechanical character of all processes. It was that rigor which made him postulate the variability of the speed of light and its being subject to gravitational attraction, just as any other material phenomenon and entity was subject to it. His pondering of such ideas could naturally raise in his mind the idea of the bending of light in strong gravitational fields and make him search for a method of determining it with accuracy. (P 937)

In Einstein's popular accounts of relativity Soldner is never mentioned. (P 937)