Johann Lambert and the Italian Jesuit and mathematician Giovanni Sacchetti first conceived of non-Euclidean geometry, later developed in detail by Riemann, Gauss, Bolyai, and Lobachevsky in the early 19th century. This would later form the basis of Schwarzschild’s insight, which in 1900 proposed that the geometry of the universe is not flat according to Euclid, but curved according to non-Euclidean geometries.
