General relativity and what other theoretical foundation underlie the Big Bang model ?
While the scientific community was once divided between supporters of two different expanding universe theories — the Big Bang and the Steady State theory , observational confirmation of the Big Bang scenario came with the discovery of the cosmic microwave background radiation in 1964 , and later when its spectrum ( i.e. , the amount of radiation measured at each wavelength ) was found to match that of thermal radiation from a black body .