cosmic microwave background: a standalone construct

Ralph Alpher and Robert Herman first predicted this radiation in 1948, reasoning that a hot, dense early universe should have left a faint thermal glow that cooled to a few degrees above absolute zero as space expanded. Arno Penzias and Robert Wilson detected it by accident in 1965 as a uniform excess microwave hiss their radio antenna could not otherwise explain, and the measurement quickly became the strongest observational support for the Big Bang model. The cosmic microwave background is the oldest light in the universe, released about 380,000 years after the Big Bang when the cooling plasma first became transparent to photons, and today it reaches Earth from every direction as microwaves with an almost perfect blackbody spectrum (radiation whose intensity across wavelengths depends only on temperature) at about 2.7 kelvin. Its temperature is nearly the same across the whole sky, and the tiny departures of a few parts in one hundred thousand map the density ripples in the infant universe that later grew into galaxies. Precise measurement of its spectrum by the COBE FIRAS instrument in the 1990s confirmed the blackbody form to high accuracy, and the field remains a primary source of the numbers cosmologists use to estimate the age, composition, and geometry of the universe.[1][2][3]

Unit

A diffuse background radiation field, characterised by its blackbody temperature (about 2.725 K) and by the angular pattern of its faint temperature anisotropies

Recovery means

Not applicable

Measured by

Recorded with radiometers and telescopes on satellites (COBE, WMAP, Planck), balloons, and the ground that measure its intensity, spectrum, angular temperature anisotropies, and polarisation across the sky