# Nova Geminorum 1912 and the Origin of the Idea of Gravitational Lensing

## TL;DR

This paper reexamines Einstein's early calculations and correspondence to explore the origins of the idea of gravitational lensing, linking it to Nova Geminorum 1912 and his development of general relativity.

## Contribution

It uncovers new historical evidence suggesting Einstein's early interest in gravitational lensing around 1912-1915, connecting it to observational events and his theoretical progress.

## Key findings

- Einstein's early notebooks contain calculations related to gravitational lensing from 1912.
- A previously unknown letter indicates Einstein considered lensing as an explanation for new stars in 1915.
- The appearance of Nova Geminorum 1912 may have influenced Einstein's initial thoughts on lensing.

## Abstract

Einstein's early calculations of gravitational lensing, contained in a scratch notebook and dated to the spring of 1912, are reexamined. A hitherto unknown letter by Einstein suggests that he entertained the idea of explaining the phenomenon of new stars by gravitational lensing in the fall of 1915 much more seriously than was previously assumed. A reexamination of the relevant calculations by Einstein shows that, indeed, at least some of them most likely date from early October 1915. But in support of earlier historical interpretation of Einstein's notes, it is argued that the appearance of Nova Geminorum 1912 (DN Gem) in March 1912 may, in fact, provide a relevant context and motivation for Einstein's lensing calculations on the occasion of his first meeting with Erwin Freundlich during a visit in Berlin in April 1912. We also comment on the significance of Einstein's consideration of gravitational lensing in the fall of 1915 for the reconstruction of Einstein's final steps in his path towards general relativity.