Kip Thorne identifies the "golden age of general relativity" as the period roughly from 1960 to 1975, during which the study of general relativity, which had previously been regarded as something of a curiosity, entered the mainstream of theoretical physics. During this period, many of the concepts and terms which continue to inspire the imaginations of gravitation researchers and the general public were introduced, including black holes and gravitational singularities. At the same time, in a closely related development, the study of physical cosmology entered the mainstream and the Big Bang became well established.