Discovery of cosmic microwave background radiation

The discovery of cosmic microwave background radiation constitutes a major development in modern physical cosmology. In 1964, US physicist Arno Allan Penzias and radio-astronomer Robert Woodrow Wilson discovered the cosmic microwave background (CMB), estimating its temperature as 3.5 K, as they experimented with the Holmdel Horn Antenna.^[1]^[2] The new measurements were accepted as important evidence for a hot early Universe (big bang theory) and as evidence against the rival steady state theory^[3] as theoretical work around 1950^[4] showed the need for a CMB for consistency with the simplest relativistic universe models. In 1978, Penzias and Wilson were awarded the Nobel Prize for Physics for their joint measurement. There had been a prior measurement of the cosmic background radiation (CMB) by Andrew McKellar in 1941 at an effective temperature of 2.3 K using CN stellar absorption lines observed by W. S. Adams.^[5] Although no reference to the CMB is made by McKellar, it was not until much later^[6] after the Penzias and Wilson measurements that the significance of this measurement was understood.

^ Cite error: The named reference PenziasWilson65CMB was invoked but never defined (see the help page).
^ Cite error: The named reference NYT-20230905 was invoked but never defined (see the help page).
^ Cite error: The named reference Dicke65 was invoked but never defined (see the help page).
^ Sciama, D. W. (1990). Mandolesi, N.; Vittorio, N. (eds.). "The Impact of the CMB Discovery on Theoretical Cosmology". The Cosmic Microwave Background: 25 Years Later. Astrophysics and Space Science Library. Dordrecht: Springer Netherlands: 1–15. doi:10.1007/978-94-009-0655-6_1. ISBN 978-94-009-0655-6.
^ Cite error: The named reference McKellar was invoked but never defined (see the help page).
^ Cite error: The named reference Thaddeus1972 was invoked but never defined (see the help page).

[PenziasWilson65CMB-1] Cite error: The named reference PenziasWilson65CMB was invoked but never defined (see the help page).

[NYT-20230905-2] Cite error: The named reference NYT-20230905 was invoked but never defined (see the help page).

[Dicke65-3] Cite error: The named reference Dicke65 was invoked but never defined (see the help page).

[4] Sciama, D. W. (1990). Mandolesi, N.; Vittorio, N. (eds.). "The Impact of the CMB Discovery on Theoretical Cosmology". The Cosmic Microwave Background: 25 Years Later. Astrophysics and Space Science Library. Dordrecht: Springer Netherlands: 1–15. doi:10.1007/978-94-009-0655-6_1. ISBN 978-94-009-0655-6.

[McKellar-5] Cite error: The named reference McKellar was invoked but never defined (see the help page).

[Thaddeus1972-6] Cite error: The named reference Thaddeus1972 was invoked but never defined (see the help page).

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