Cosmological concept · Cosmology

The Expansion of the Universe

Cosmology & UniverseEstablished Science

Definition

The observed stretching of space itself, which carries galaxies apart at rates proportional to their distance.

Scientific overview

Space between galaxies is expanding, so distant galaxies recede from us — and from each other — with a speed proportional to their distance. Galaxies are not moving through space so much as being carried along by the growth of space itself.

Evidence

The redshift–distance relation of galaxies
The cosmic microwave background
Baryon acoustic oscillations

Rests on

General Relativity

Related discoveries & objects

The Expansion of the Universe

Related scientists

Edwin Hubble

Georges Lemaître

Cosmological Redshift

The Hubble–Lemaître Law

The Hubble Constant

Knowledge connections

Sources & references

The primary and reference sources this topic draws on.

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.
Planck CollaborationESA Planck mission / Planck Collaboration
Cosmic microwave background maps and the cosmological parameters of the ΛCDM model.

Quick facts

Type: Cosmological concept
Field: Cosmology
Consensus: Established Science

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 universe is expanding, with distant galaxies receding at rates proportional to their distance (the Hubble–Lemaître law), a relation first established observationally in the 1920s.
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 relation between distance and radial velocity among extra-galactic nebulae

Edwin Hubble · PNAS 15 (3), 168–173 · 1929

Proceedings of the National Academy of Sciences · doi:10.1073/pnas.15.3.168

Cite (APA / BibTeX)

Edwin Hubble (1929). A relation between distance and radial velocity among extra-galactic nebulae. PNAS 15 (3), 168–173. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.15.3.168

@misc{cite:hubble-1929,
  title        = {A relation between distance and radial velocity among extra-galactic nebulae},
  author       = {Edwin Hubble},
  organization = {Proceedings of the National Academy of Sciences},
  howpublished = {PNAS 15 (3), 168–173},
  year         = {1929},
  doi          = {10.1073/pnas.15.3.168},
  url          = {https://doi.org/10.1073/pnas.15.3.168},
  note         = {The velocity–distance relation (Hubble's law).}
}

Institutional pageThe Expanding Universe — NASA Universe

NASA

Cite (APA / BibTeX)

NASA (n.d.). The Expanding Universe — NASA Universe. NASA. https://science.nasa.gov/

@misc{cite:nasa-cosmo-the-expanding-universe,
  title        = {The Expanding Universe — NASA Universe},
  organization = {NASA},
  year         = {n.d.},
  url          = {https://science.nasa.gov/},
  note         = {NASA science overview: The Expanding Universe.}
}

The Expansion of the Universe

Definition

Scientific overview

Evidence

Rests on

Related discoveries & objects

Related scientists

Related topics

Knowledge connections

Sources & references