The next most important observational evidence was the discovery of cosmic microwave background radiation in 1964. (sciencedaily.com)
Problems with the theory became apparent in the 1960s, and soon the discovery of the cosmic microwave background radiation killed the steady - state theory. (discovermagazine.com)
The famous cosmic microwave background radiation, considered to be the definitive proof of the big bang, fills the sky. (scientificamerican.com)