Cosmic background radiation is

electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) li ...

from the Big Bang. The origin of this radiation depends on the region of the

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...

that is observed. One component is the

cosmic microwave background In Big Bang cosmology the cosmic microwave background (CMB, CMBR) is electromagnetic radiation that is a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all spac ...

. This component is redshifted

photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they a ...

s that have freely streamed from an epoch when the Universe became transparent for the first time to radiation. Its discovery and detailed observations of its properties are considered one of the major confirmations of the Big Bang. The discovery (by chance in 1965) of the cosmic background radiation suggests that the early universe was dominated by a radiation field, a field of extremely high temperature and pressure. The Sunyaev–Zel'dovich effect shows the phenomena of radiant cosmic background radiation interacting with "

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

" clouds distorting the spectrum of the radiation. There is also background radiation in the

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

x-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

s, etc., with different causes, and they can sometimes be resolved into an individual source. See

cosmic infrared background Cosmic infrared background is infrared radiation caused by stellar dust. History Recognizing the cosmological importance of the darkness of the night sky ( Olbers' paradox) and the first speculations on an extragalactic background light date ...

and

X-ray background The observed X-ray background is thought to result from, at the "soft" end (below 0.3 keV), galactic X-ray emission, the "galactic" X-ray background, and, at the "hard" end (above 0.3keV), from a combination of many unresolved X-ray sources outside ...

. See also

cosmic neutrino background The cosmic neutrino background (CNB or CB) is the universe's background particle radiation composed of neutrinos. They are sometimes known as relic neutrinos. The CB is a relic of the Big Bang; while the cosmic microwave background radiation (CM ...

and extragalactic background light.

Timeline of significant events

1896: Charles Édouard Guillaume estimates the "radiation of the stars" to be 5.6 K. 1926: Sir Arthur Eddington estimates the non-thermal radiation of starlight in the galaxy has an effective temperature of 3.2 K

1930s: Erich Regener calculates that the non-thermal spectrum of cosmic rays in the galaxy has an effective temperature of 2.8 K. 1931: The term ''microwave'' first appears in print: "When trials with wavelengths as low as 18 cm were made known, there was undisguised surprise that the problem of the micro-wave had been solved so soon." ''Telegraph & Telephone Journal'' XVII. 179/1" 1938:

Nobel Prize The Nobel Prizes ( ; sv, Nobelpriset ; no, Nobelprisen ) are five separate prizes that, according to Alfred Nobel's will of 1895, are awarded to "those who, during the preceding year, have conferred the greatest benefit to humankind." Alfr ...

winner (1920) Walther Nernst re-estimates the cosmic ray temperature as 0.75 K. 1946: The term "

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...

" is first used in print in an astronomical context in an article "Microwave Radiation from the Sun and Moon" by

Robert Dicke Robert Henry Dicke (; May 6, 1916 – March 4, 1997) was an American astronomer and physicist who made important contributions to the fields of astrophysics, atomic physics, cosmology and gravity. He was the Albert Einstein Professor in Scienc ...

and

Robert Beringer The name Robert is an ancient Germanic given name, from Proto-Germanic "fame" and "bright" (''Hrōþiberhtaz''). Compare Old Dutch ''Robrecht'' and Old High German ''Hrodebert'' (a compound of '' Hruod'' ( non, Hróðr) "fame, glory, honou ...

. 1946:

predicts a microwave background radiation temperature of 20 K (ref: Helge Kragh) 1946: Robert Dicke predicts a microwave background radiation temperature of "less than 20 K" but later revised to 45 K (ref: Stephen G. Brush). 1946:

George Gamow George Gamow (March 4, 1904 – August 19, 1968), born Georgiy Antonovich Gamov ( uk, Георгій Антонович Гамов, russian: Георгий Антонович Гамов), was a Russian-born Soviet and American polymath, theoret ...

estimates a temperature of 50 K. 1948:

Ralph Alpher Ralph Asher Alpher (February 3, 1921 – August 12, 2007) was an American cosmologist, who carried out pioneering work in the early 1950s on the Big Bang model, including Big Bang nucleosynthesis and predictions of the cosmic microwave backgroun ...

and

Robert Herman Robert Herman (August 29, 1914 – February 13, 1997) was an American scientist, best known for his work with Ralph Alpher in 1948–50, on estimating the temperature of cosmic microwave background radiation from the Big Bang explosion. Biograp ...

re-estimate Gamow's estimate at 5 K. 1949: Ralph Alpher and Robert Herman re-re-estimate Gamow's estimate at 28 K. 1960s: Robert Dicke re-estimates a MBR (microwave background radiation) temperature of 40 K (ref: Helge Kragh). 1965:

Arno Penzias Arno Allan Penzias (; born April 26, 1933) is an American physicist, radio astronomer and Nobel laureate in physics. Along with Robert Woodrow Wilson, he discovered the cosmic microwave background radiation, which helped establish the Big Bang ...

and

Robert Woodrow Wilson Robert Woodrow Wilson (born January 10, 1936) is an American astronomer who, along with Arno Allan Penzias, discovered cosmic microwave background radiation (CMB) in 1964. The pair won the 1978 Nobel Prize in Physics for their discovery. While ...

measure the temperature to be approximately 3 K. Robert Dicke,

P. J. E. Peebles Phillip James Edwin Peebles (born April 25, 1935) is a Canadians, Canadian-Americans, American astrophysicist, astronomer, and theoretical physical cosmology, cosmologist who is currently the Albert Einstein Professor in Science, Emeritus, at ...

, P. G. Roll and D. T. Wilkinson interpret this radiation as a signature of the Big Bang.

References

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External links

The Diffuse X-ray and Gamma-ray Background & Deep Fields
Observational astronomy Physical cosmology Concepts in astronomy Electromagnetic radiation