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Dark energy and accelerating expansion

Saul PerlmutterBrian SchmidtAdam RiessDESI Collaboration

This page delivers no verdict; it presents claims and evidence with their sources. No theory in science is absolute. Method

For everyone

In 1998 distant supernovae appeared fainter than expected, which was interpreted as the expansion of the universe accelerating. The unknown cause was named "dark energy". Data released by DESI in 2025 hinted that dark energy may not be constant but may change over time; this result is not yet settled.

For specialists

Type Ia supernovae were used as "standard candles"; a positive cosmological constant (Λ) gave the best fit. DESI DR2 combined baryon acoustic oscillation measurements from more than 14 million galaxies and quasars with CMB and supernova data. In this combined analysis a time-varying dark energy (w₀wₐ parametrisation) was preferred over ΛCDM at 2.8–4.2σ. The significance depends on which supernova catalogue is used, and some researchers argue that systematic effects could account for the result.

Claims

Evidence

Supporting

Observation

High-redshift Type Ia supernovae were observed to be fainter than expected in a decelerating or coasting universe.[1][2]

Measurement

DESI's three-year data, combined with CMB and supernova data, preferred evolving dark energy over constant dark energy.[3]

Statistics / meta-analysis

When the same data were examined taking into account how supernova properties change with redshift, a strong result in favour of acceleration was found; combined with other cosmological data, acceleration is also supported with high confidence.[5]

Challenging

Statistics / meta-analysis

A re-analysis of the 740-supernova JLA catalogue with a different statistical method argued that the evidence for accelerating expansion is below 3 sigma, that is, "marginal".[4]

Open questions

Connections

Parent

Astronomy and cosmology

Related

The beginning of the universe and the Big Bang

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Sources

  1. ArticleRiess, A. G. et al. (1998). Observational evidence from supernovae for an accelerating universe and a cosmological constant. The Astronomical Journal 116, 1009–1038DOI 10.1086/300499archive
  2. ArticlePerlmutter, S. et al. (1999). Measurements of Ω and Λ from 42 high-redshift supernovae. The Astrophysical Journal 517, 565–586DOI 10.1086/307221archive
  3. PreprintDESI Collaboration (2025). DESI DR2 Results II: Measurements of baryon acoustic oscillations and cosmological constraintsarXiv:2503.14738archive
  4. ArticleNielsen, J. T.; Guffanti, A.; Sarkar, S. (2016). Marginal evidence for cosmic acceleration from Type Ia supernovae. Scientific Reports 6, 35596DOI 10.1038/srep35596archive
  5. ArticleRubin, D.; Hayden, B. (2016). Is the expansion of the universe accelerating? All signs point to yes. The Astrophysical Journal Letters 833, L30DOI 10.3847/2041-8213/833/2/L30archive

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APA

Athena contributors. (2026). Dark energy and accelerating expansion. Athena: The tree of human knowledge. Retrieved November 1, 2026, from https://latifkedi.github.io/athena/en/d/karanlik-enerji/

BibTeX
@misc{athena_karanlik_enerji,
  title        = {Dark energy and accelerating expansion},
  author       = {{Athena contributors}},
  year         = {2026},
  howpublished = {\url{https://latifkedi.github.io/athena/en/d/karanlik-enerji/}},
  note         = {Athena: The tree of human knowledge. Accessed: 2026-11-01}
}

Added: September 27, 2026 · Last changed: September 28, 2026 · Page history

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