When I started teaching college in 1964, the required reading for my general studies science course included two articles by two prominent physicists published in Scientific American eight years previously. George Gamow, a principal architect of the big bang theory, made the case for a universe that began billions of years ago as an explosion from an infinitely dense and infinitely small seed of energy. Fred Hoyle, stalwart champion of the steady state theory, took the stand for an infinite universe with no beginning and no end, in which matter is continuously created in the space between the galaxies.
Both theories explained the outward rush of the galaxies discovered by Vesto Slipher, Edwin Hubble and Milton Humason in the first decades of the century. Both theories had strengths and weaknesses. For example, the big bang successfully accounted for the known abundances of hydrogen and helium in the universe but posited an embarrassing beginning that could not be explained. The steady state theory avoided the stumbling block of a universe that seemed to come from nowhere but replaced it with many little unexplained beginnings (those particles of matter appearing continuously from nothing). Yet the big bang theory made one prediction that was testable: if the universe began in a blaze of luminosity, a degraded remnant of that radiation should still permeate the cosmos, and the precise spectral distribution of this microwave-frequency background could be calculated.