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.