Debating Relativistic Cosmology, 1917–1924

Physical astronomy as we know it today matured during the latter half of the twentieth century. It was preceded by a period Jean Eisenstaedt has dubbed the “low water mark” in general relativity (GR), covering roughly the period 1925 to 1955 (Eisenstaedt 1988b). Starting in the 1960s, however, a series of startling developments helped pave the way for what has since been called the “renaissance of general relativity,” which suddenly took on great significance for astrophysics and cosmology. In the days of Einstein and Eddington, one could imagine a gravitational field so strong that it would produce a black hole, a true space–time singularity. People talked about such things, but hardly anyone believed they could actually occur (Thorne 1994). Yet after Penrose and Hawking proved the celebrated singularity theorems (Earman 1999; Hawking and Ellis 1973), experts began to look for evidence that might confirm the existence of black holes. This was only one of many unexpected developments in GR that helped to inaugurate a revolutionary shift in our understanding of the universe. Truly momentous discoveries soon followed, leading to findings that would eventually shatter the quaint universe inhabited by Albert Einstein at the time he unveiled his general theory of relativity.