Expansion of the universe
The increase in distance between gravitationally unbound parts of the universe.
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Over time, the distances separating parts of the observable universe that are not bound by gravity intrinsically increase.[1] Observations show that galaxies far from Earth are moving away in every direction, and a galaxy's speed is directly linked to how far away it is.[2] Because the universe appears homogeneous and isotropic on the largest scales, and because of the observed relationship known as Hubble's law, the present-day expansion is uniform.[2]
Quick Facts
- Discovery period
- 1920s
- Key contributors
- Vesto Slipher
- Alexander Friedmann
- Knut Lundmark
- Georges Lemaître
- Edwin Hubble
- Field
- Cosmology
- Defining law
- Hubble's law (Hubble–Lemaître law)
- Current model
- Lambda-CDM model
Facts from the source article.
Key facts and history
Hubble himself did not associate the relationship now called Hubble's law to the expansion of the universe, and his estimate of the proportionality constant was too large by a factor of 7.[3] Between 1912 and 1914, Vesto Slipher observed that light from distant galaxies exhibited a redshift, which was subsequently understood to mean those galaxies were moving away from Earth.[4] Georges Lemaître, in 1927, solved Einstein's equations and used data from Slipher and Hubble to propose that a galaxy's recessional velocity and its distance follow a linear pattern.[5] Edwin Hubble, in 1929, used a variety of methods and verified techniques to solidly confirm this linear relationship.[5]
Observations of supernovae, which earned the 2011 Nobel Prize in Physics, demonstrated that the universe's expansion is currently speeding up.[6]
What the research sources say
The Space.com account states that Belgian priest and cosmologist Georges Lemaître published his discovery of the expansion of the universe in an obscure journal two years before Edwin Hubble.[7] The same source notes that Edwin Hubble has long been lauded for his 1929 discovery that the universe is expanding.[7] Ned Wright's Cosmology Tutorial explains that the homogeneity of the universe must be defined on a surface of constant proper time since the Big Bang.[8] Wright's tutorial also states that precise measurements of deviations of D_L from cz/H_o are what tell us that the expansion of the universe is accelerating.[8]
The tutorial further notes that current density estimates suggest the matter density is between 0.2 to 1 times the critical density, requiring that most matter in the universe is dark.[8]
References
- Wikipedia, "Expansion of the universe" (CC BY-SA 4.0), which cites: Overbye, "Cosmos Controversy: The Universe Is Expanding, but How Fast?", The New York Times, 20 February 2017 (original not read by us) en.wikipedia.org
- Wikipedia, "Expansion of the universe" (CC BY-SA 4.0), which cites: Longair, "Galaxy Formation", 2023 (we also read that source) en.wikipedia.org
- Wikipedia, "Expansion of the universe" (CC BY-SA 4.0), which cites: Bahcall, "Hubble's Law and the expanding universe", Proceedings of the National Academy of Sciences, 2015-03-17, p. 3173–3175; Baade, W. (1944) "The resolution of Messier 32, NGC 205, and the central region of the Andromeda nebula". ApJ 100. pp. 137–146; Baade, W. (1956) "The period–luminosity relation of the Cepheids". PASP 68. pp. 5–16; Allen, "Section 2: The Great Debate and the Great Mistake: Shapley, Hubble, Baade", The Cepheid Distance Scale: A History (original not read by us) en.wikipedia.org
- Wikipedia, "Expansion of the universe" (CC BY-SA 4.0), which cites: Slipher, "The Radial Velocity of the Andromeda Nebula", Lowell Observatory Bulletin, 1913, p. 56–57; "Vesto Slipher – American astronomer" (original not read by us) en.wikipedia.org
- Wikipedia, "Expansion of the universe" (CC BY-SA 4.0), which cites: Steer, "Who discovered Universe expansion?", Nature, October 2012, p. 176; Livio, "Mystery of the missing text solved", Nature, 2011-11-10, p. 171–173; Lemaître, "Un Univers homogène de masse constante et de rayon croissant rendant compte de la vitesse radiale des nébuleuses extra-galactiques", Annales de la Société Scientifique de Bruxelles, 1927, p. 49–59; Steer, "Who discovered Universe expansion?", Nature, October 2012, p. 176; "Astronomer sleuth solves mystery of Big Cosmos discovery", Space.com, 14 November 2011 (we also en.wikipedia.org
- Wikipedia, "Expansion of the universe" (CC BY-SA 4.0), which cites: "The Nobel Prize in Physics 2011", NobelPrize.org (original not read by us) en.wikipedia.org
- "Astronomer sleuth solves mystery of Big Cosmos discovery", Space.com, 14 November 2011. facts only, no text reused. space.com
- Wright, "Cosmology Tutorial – Part 2", Ned Wright's Cosmology Tutorial. facts only, no text reused. astro.ucla.edu
Each numbered sentence above was checked against the source it cites before publication. Sentences citing Wikipedia adapt text from the English Wikipedia article Expansion of the universe (contributors), used under CC BY-SA 4.0; this entry is available under the same licence. Other sources were used for facts only; no text or images are copied from them.
More in Cosmology Concepts
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Expansion of the universe (CC BY-SA 4.0).
- Word definitions: the , each quoted from its Wikipedia article.
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