Abstract

The recently published Vol. 8 of Einstein’s Collected Papers brings together for the first time all extant letters and postcards documenting the famous debate of 1916–18 between Einstein and the Leyden astronomer Willem de Sitter (1872–1934), over, as they referred to it, the relativity of inertia. It was in the course of this debate that the first two relativistic cosmological models were proposed: the “Einstein cylinder world,” filled with a uniform static mass distribution; and the completely empty “De Sitter hyperboloid world” (a name introduced in..