The chapter provides a brief overview of the first three major eras, out of four, in the development of cosmology. The first era started with “prehistory” of cosmology in antiquity, continued with the major contributions of Newton and the nineteenth-century debates on thermodynamics conditions at the cosmic scale, and ended with a “quantum leap” in relevant observational capacities at the beginning of the twentieth century. The second era saw cosmology develop as a mathematical game of sorts, rather than a physical theory predicated on Einstein’s General Theory of Relativity. It was marked by Einstein’s static model of the universe and a static model by De Sitter. A cosmological revolution began in the third era (from 1929 to 1948), with the development of expanding models of the universe that captured its physical dynamics.

The chapter summarizes the historical trajectory of alternatives to the orthodox explanation of the CMB, which lacked strife or “great controversy” prior to the 1965 discovery. Various alternative explanations were discussed and criticized to differing extents, but no consensus emerged. The engagement and observational refutations, most decisively with the COBE results, came in gradually without significant social and professional jitters. Yet careful theoretical considerations of the alternatives and the challenges they offered prepared the way for later convergence when overwhelming empirical evidence in favor of the emerging orthodoxy still did not exist. Some of the most authoritative physics figures worked on alternatives because the wiggle room was quite wide. This was an epistemically responsible response to the prolonged state of underdetermination of theories by existing limited (and fluctuating) evidence. In a concluding discussion, the chapter compares specific challenges and limitations of cosmology to those of experimentally driven fields of physics.

As the chapter points out, standard cosmology textbooks offer a triumphant account of the Hot Big Bang model as the orthodoxy that was almost instantly accepted with the discovery of the CMB by Penzias and Wilson. Yet this historical account does not reveal the whole story of the orthodoxy’s gradual ascent and the all but forgotten, but at the time important, side roads. We argue that historical analysis must shun the triumphant partial account, but resist eliminating the current understanding as irrelevant for understanding the past. If approached in a balanced manner, the story of the CMB evidence often diverges from the values that unequivocally lent support to the orthodoxy, thus opening the space for alternative interpretations.