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The cosmic microwave background (CMB, CMBR), or relic radiation, is microwave radiation that fills all space in the observable universe.

With a standard optical telescope, the background space between stars and galaxies is almost completely dark. However, a sufficiently sensitive radio telescope detects a faint background glow that is almost uniform and is not associated with any star, galaxy, or other object. Its energy density exceeds that of all the photons emitted by all the stars in the history of the universe. The CMB is the key experimental evidence of the Big Bang theory for the origin of the universe.

The cosmic microwave background radiation is an emission of uniform black body thermal energy coming from all directions.

Alpher and Herman were able to estimate the temperature of the cosmic microwave background to be 5 K.

Dicke's colleagues at Princeton University, began constructing a Dicke radiometer to measure the cosmic microwave background.

Rashid Sunyaev, using the alternative name relic radiation, calculated the observable imprint that these inhomogeneities would have on the cosmic microwave background.

RELIKT-1, a Soviet cosmic microwave background anisotropy experiment on board the Prognoz 9 satellite (launched 1 July 1983), gave the first upper limits on the large-scale anisotropy.

Inspired by the COBE results, a series of ground and balloon-based experiments measured cosmic microwave background anisotropies on smaller angular scales over the next two decades. They ruled out cosmic strings as a major component of cosmic structure formation and suggested cosmic inflation was the right theory of structure formation.

These measurements were able to rule out cosmic strings as the leading theory of cosmic structure formation, and suggested cosmic inflation was the right theory.

On 21 March 2013, the European-led research team behind the Planck cosmology probe released the mission's all-sky map of the cosmic microwave background.

The cosmic microwave background radiation and the cosmological redshift-distance relation are together regarded as the best available evidence for the Big Bang event. Most of the radiation energy in the universe is in the cosmic microwave background, making up a fraction of roughly 6×10−5 of the total density of the universe. Two of the greatest successes of the Big Bang theory are its prediction of the almost perfect black body spectrum and its detailed prediction of the anisotropies in the cosmic microwave background.

The anisotropy, or directional dependency, of the cosmic microwave background is divided into two types: primary anisotropy, due to effects that occur at the surface of last scattering and before; and secondary anisotropy, due to effects such as interactions of the background radiation with intervening hot gas or gravitational potentials, which occur between the last scattering surface and the observer. The structure of the cosmic microwave background anisotropies is principally determined by two effects: acoustic oscillations and diffusion damping (also called collisionless damping or Silk damping).

Models of "slow-roll" cosmic inflation in the early universe predicts primordial gravitational waves that would impact the polarisation of the cosmic microwave background, creating a specific pattern of B-mode polarization.

Although Shamonov did not recognize it at the time, it is now clear that Shmaonov did observe the cosmic microwave background at a wavelength of 3.2 cm 1990 – FIRAS on the Cosmic Background Explorer (COBE) satellite measures the black body form of the CMB spectrum with exquisite precision, and shows that the microwave background has a nearly perfect black-body spectrum with T = 2.73 K and thereby strongly constrains the density of the intergalactic medium. January 1992 – Scientists that analysed data from the RELIKT-1 report the discovery of anisotropy in the cosmic microwave background at the Moscow astrophysical seminar. 1992 – Scientists that analysed data from COBE DMR report the discovery of anisotropy in the cosmic microwave background. 1995 – The Cosmic Anisotropy Telescope performs the first high resolution observations of the cosmic microwave background.

Quick Facts

• 1995 – The Cosmic Anisotropy Telescope performs the first high resolution observations of the cosmic microwave background.
• The cosmic microwave background radiation is an emission of uniform black body thermal energy coming from all directions.
• Models of "slow-roll" cosmic inflation in the early universe predicts primordial gravitational waves that would impact the polarisation of the cosmic microwave background, creating a specific pattern of B-mode polarization.
• Most of the radiation energy in the universe is in the cosmic microwave background, making up a fraction of roughly 6×10−5 of the total density of the universe.
• Alpher and Herman were able to estimate the temperature of the cosmic microwave background to be 5 K.

Source material: Wikipedia - "Cosmic microwave background". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.