Cosmological concept · Cosmology

The Cosmic Microwave Background

Cosmology & UniverseEstablished Science

Definition

The faint, uniform microwave glow left over from recombination — the oldest light in the Universe.

Scientific overview

The CMB is relic radiation released 380,000 years after the Big Bang, now cooled by expansion to just 2.7 K. Its near-perfect uniformity, tiny temperature fluctuations (1 part in 100,000), and detailed spectrum encode the composition, geometry, and age of the Universe.

Evidence

Its perfect blackbody spectrum (COBE)
Temperature anisotropies (WMAP, Planck) that fix the cosmological parameters

Current measurements

Temperature

2.7255 ± 0.0006 K

Planck Collaboration

Rests on

Recombination

Related discoveries & objects

The Cosmic Microwave Background

Measured by

COBE (Cosmic Background Explorer)

WMAP (Wilkinson Microwave Anisotropy Probe)

Planck

Related scientists

Arno Penzias

Robert Wilson

Knowledge connections

Predicted byThe Big Bang
Predicted byCosmic Inflation
Predicted byRecombination
Depends onRecombination
Part of modelThe Lambda-CDM Model
Related toThe Cosmic Microwave Background
Studied byArno Penzias
Studied byRobert Wilson
Measured byCOBE (Cosmic Background Explorer)
Measured byWMAP (Wilkinson Microwave Anisotropy Probe)
Measured byPlanck
Related toThe Lambda-CDM Model
Associated withCMB Measurements
Associated withScalar Spectral Index (ns)
Associated withEarly Dark Energy
Associated withQuantum Fluctuations
Associated withThe Cosmic Neutrino Background
Associated withThe GZK Limit

Sources & references

The primary and reference sources this topic draws on.

Planck CollaborationESA Planck mission / Planck Collaboration
Cosmic microwave background maps and the cosmological parameters of the ΛCDM model.
NASANational Aeronautics and Space Administration
Mission data, planetary science, space telescopes, and public-domain imagery.
Most NASA-produced imagery is in the public domain; individual items are checked for usage terms before publication.

Quick facts

Type: Cosmological concept
Field: Cosmology
Consensus: Established Science
Part of model: The Lambda-CDM Model

Scientific consensus

Established Science

Observationally confirmed and consistent across all leading models.

Quality & authority

Complete

Reviewed

Description: Complete
Source coverage: Complete
Relationship coverage: Complete
Review coverage: Complete
Citation coverage: Complete
Image coverage: Not applicable

Curated from authoritative sources. See source quality.

Provenance & sources

review 2026.1

Asteria Scientific Review Process · verification: sourced · accurate

High evidenceconfirmed
The cosmic microwave background is relic thermal radiation from the early universe, discovered in 1965 and measured to be a near-perfect blackbody at about 2.725 K.
Source: ESA — Planck Collaboration
- Planck 2018 results. VI. Cosmological parameters, Astronomy & Astrophysics 641, A6 (2020)doi:10.1051/0004-6361/201833910

Reviewed by the internal Asteria Scientific Review Process — not an external institutional review. See the evidence framework and authority dashboard.

Scientific citations

Real, source-backed references — primary papers first, then datasets and institutional sources. Formatted through the citation engine; nothing is fabricated.

Peer-reviewed paperA Measurement of Excess Antenna Temperature at 4080 Mc/s

Arno A. Penzias & Robert W. Wilson · The Astrophysical Journal 142, 419–421 · 1965

The Astrophysical Journal · doi:10.1086/148307

Cite (APA / BibTeX)

Arno A. Penzias & Robert W. Wilson (1965). A Measurement of Excess Antenna Temperature at 4080 Mc/s. The Astrophysical Journal 142, 419–421. The Astrophysical Journal. https://doi.org/10.1086/148307

@misc{cite:penzias-wilson-1965,
  title        = {A Measurement of Excess Antenna Temperature at 4080 Mc/s},
  author       = {Arno A. Penzias and Robert W. Wilson},
  organization = {The Astrophysical Journal},
  howpublished = {The Astrophysical Journal 142, 419–421},
  year         = {1965},
  doi          = {10.1086/148307},
  url          = {https://doi.org/10.1086/148307},
  note         = {Discovery of the cosmic microwave background.}
}

Peer-reviewed paperPlanck 2018 results. VI. Cosmological parameters

Planck Collaboration · Astronomy & Astrophysics 641, A6 · 2020

ESA — Planck Collaboration · doi:10.1051/0004-6361/201833910

Cite (APA / BibTeX)

Planck Collaboration (2020). Planck 2018 results. VI. Cosmological parameters. Astronomy & Astrophysics 641, A6. ESA — Planck Collaboration. https://doi.org/10.1051/0004-6361/201833910

@misc{cite:planck-2018-cosmological-parameters,
  title        = {Planck 2018 results. VI. Cosmological parameters},
  author       = {Planck Collaboration},
  organization = {ESA — Planck Collaboration},
  howpublished = {Astronomy & Astrophysics 641, A6},
  year         = {2020},
  doi          = {10.1051/0004-6361/201833910},
  url          = {https://doi.org/10.1051/0004-6361/201833910},
  note         = {Cosmological parameters from the final Planck data release.}
}

Mission pagePlanck — ESA Science

European Space Agency

Cite (APA / BibTeX)

European Space Agency (n.d.). Planck — ESA Science. European Space Agency. https://www.esa.int/Science_Exploration/Space_Science/Planck

@misc{cite:esa-planck,
  title        = {Planck — ESA Science},
  organization = {European Space Agency},
  year         = {n.d.},
  url          = {https://www.esa.int/Science_Exploration/Space_Science/Planck},
  note         = {ESA Planck mission — high-precision CMB maps.}
}

Institutional pageCosmic Microwave Background — NASA Universe

NASA

Cite (APA / BibTeX)

NASA (n.d.). Cosmic Microwave Background — NASA Universe. NASA. https://science.nasa.gov/

@misc{cite:nasa-cosmo-cosmic-microwave-background,
  title        = {Cosmic Microwave Background — NASA Universe},
  organization = {NASA},
  year         = {n.d.},
  url          = {https://science.nasa.gov/},
  note         = {NASA science overview: Cosmic Microwave Background.}
}

Historical referenceThe Nobel Prize in Physics 1978

1978

The Nobel Prize

Cite (APA / BibTeX)

The Nobel Prize (1978). The Nobel Prize in Physics 1978. The Nobel Prize. https://www.nobelprize.org/prizes/physics/1978/

@misc{cite:nobel-physics-1978,
  title        = {The Nobel Prize in Physics 1978},
  organization = {The Nobel Prize},
  year         = {1978},
  url          = {https://www.nobelprize.org/prizes/physics/1978/},
  note         = {Penzias & Wilson (cosmic microwave background radiation).}
}