Arno Allan Penzias and Robert Woodrow Wilson , while testing some microwave-receiving equipment, discovered cosmic background radiation (CBR) which yielded "noise temperature [of] a value about 3.5 degrees K. higher than expected" and concluded it was coming in all directions with no obvious source and was not "due to radio sources of types known to exist". Robert Henry Dicke , Phillip James Edwin Peebles , and colleagues explained the "excess radiation as the residual temperature of the primeval explosion that initiated the expansion of the Universe". The implication is that intergalactic space is above absolute zero, or about 3 degrees K.  CBR together with the extant amount of helium is corroberated by extrapolation to the point in time when the Universe was a few seconds old and hot enough for nuclear reactions to occur.  This, in turn, led to a drastic shift of the consensus to favor acceptance of the big-bang cosmology.