Universe: Difference between revisions
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Completing the Universe draft: expansion of the origin and present-day sections with Planck 2018, the Lemaître 1927 and Hubble 1929 papers, and NASA sources; AI-assisted (RonzzWikiCowriter) (via update-page on MediaWiki MCP Server) |
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The universe is the | '''The universe''' is the totality of space and time, together with all the matter and energy they contain. It includes: | ||
* matter and energy, both in the ordinary forms we see around us and in the "dark" forms ([[Dark matter|dark matter]] and dark energy) whose existence is inferred mainly from their gravitational effects, organised on the largest scales into a structure known as the [[Cosmic web|cosmic web]]; | |||
* [[Spacetime]], the four-dimensional continuum in which matter and energy exist, move and interact. | |||
== Origin of the universe == | |||
= | As of August 2026, the most accepted theory of the origin of the universe is the [[Big Bang Theory|Big Bang]]: the universe began about 13.8 billion years ago in an extremely hot and dense state, and has been expanding and cooling ever since.<ref>{{#cite:Q356}}</ref><ref>{{#cite:Q1232}}</ref> | ||
[[File:Universe-timeline.jpg|thumb|upright=1.8|The history of the universe, from cosmic inflation (far left) to the present day. The expansion first slowed under the pull of gravity, then accelerated as dark energy came to dominate. Credit: NASA/WMAP Science Team (public domain).]] | |||
The earliest era that observations can probe is marked by the cosmic microwave background (CMB), the light released when the universe, a few hundred thousand years old, had cooled enough to become transparent.<ref>{{#cite:Q1232}}</ref> The CMB was mapped over the whole sky by the Planck space observatory of the [[Collective:European Space Agency|European Space Agency]]; the [[Collective:Planck Collaboration|Planck Collaboration]]'s final analysis of the mission data, published in 2020, found good consistency with the standard six-parameter model, "base ΛCDM", and the tiny temperature fluctuations it resolved are the seeds from which galaxies and all later structure grew.<ref>{{#cite:Q1232}}</ref> | |||
The Big Bang is not the only theory of the origin of the universe: alternative proposals, such as the ekpyrotic universe theory,<ref>{{#cite:Q360}}</ref> the BVG unified cosmology,<ref>{{#cite:Q389}}</ref> and the bilobular collision model,<ref>{{#cite:Q391}}</ref> remain under active research. None has so far displaced the standard ΛCDM model, which the Planck data fit well.<ref>{{#cite:Q1232}}</ref> | |||
== The universe today == | == The universe today == | ||
The universe is | === Expansion === | ||
The universe is expanding: on the largest scales, the distances between galaxies grow with time, and the more distant a galaxy is, the faster it recedes from us. In 1927, [[Person:Georges Lemaître|Georges Lemaître]] showed that general relativity admits a homogeneous universe of constant mass and increasing radius, and derived a linear relation between the distance of extra-galactic nebulae and their radial velocity.<ref>{{#cite:Q1526}}</ref> In 1929, [[Person:Edwin Hubble|Edwin Hubble]] gave the relation its observational foundation, using distances to extra-galactic nebulae measured from the Cepheid variable stars they contain.<ref>{{#cite:Q1527}}</ref> The relation, known today as the Hubble–Lemaître law (historically, Hubble's law), is characterised by the Hubble constant, H<sub>0</sub>, the present-day expansion rate; from the CMB, the Planck Collaboration measures H<sub>0</sub> = (67.4 ± 0.5) km s<sup>−1</sup> Mpc<sup>−1</sup>.<ref>{{#cite:Q1232}}</ref> | |||
=== Composition === | |||
In the standard model, the universe today consists of about 68% dark energy, about 27% dark matter, and about 5% ordinary (baryonic) matter.<ref>{{#cite:Q1232}}</ref> Ordinary matter is the stuff of stars, planets, and gas; dark matter neither emits nor absorbs light and reveals itself only through its gravity, which binds galaxies and galaxy clusters;<ref>{{#cite:Q1532}}</ref> and dark energy behaves like the cosmological constant of general relativity, driving the accelerated expansion of the universe in the standard model.<ref>{{#cite:Q1232}}</ref> | |||
=== Large-scale structure === | |||
Matter is not spread uniformly: gravity has gathered it into galaxies, groups, and clusters, which in turn form superclusters, walls, and filaments. On the very largest scales these structures arrange themselves into the cosmic web, a pattern of filaments and walls surrounding vast, nearly empty voids, which forms as gravitational attraction draws matter into ever larger concentrations.<ref>{{#cite:Q1532}}</ref> Averaged over still larger scales, the universe is homogeneous and isotropic, an assumption built into the standard model of cosmology and consistent with Planck's measurements of the CMB.<ref>{{#cite:Q1232}}</ref> | |||
== References == | |||
<references/> | |||
== Further reading == | |||
* [https://science.nasa.gov/universe/ The Universe], NASA Science | |||
* [https://www.esa.int/Science_Exploration/Space_Science/Planck Planck], European Space Agency | |||
Revision as of 13:06, 2 September 2026
The universe is the totality of space and time, together with all the matter and energy they contain. It includes:
- matter and energy, both in the ordinary forms we see around us and in the "dark" forms (dark matter and dark energy) whose existence is inferred mainly from their gravitational effects, organised on the largest scales into a structure known as the cosmic web;
- Spacetime, the four-dimensional continuum in which matter and energy exist, move and interact.
Origin of the universe
As of August 2026, the most accepted theory of the origin of the universe is the Big Bang: the universe began about 13.8 billion years ago in an extremely hot and dense state, and has been expanding and cooling ever since.[1][2]
The earliest era that observations can probe is marked by the cosmic microwave background (CMB), the light released when the universe, a few hundred thousand years old, had cooled enough to become transparent.[2] The CMB was mapped over the whole sky by the Planck space observatory of the European Space Agency; the Planck Collaboration's final analysis of the mission data, published in 2020, found good consistency with the standard six-parameter model, "base ΛCDM", and the tiny temperature fluctuations it resolved are the seeds from which galaxies and all later structure grew.[2]
The Big Bang is not the only theory of the origin of the universe: alternative proposals, such as the ekpyrotic universe theory,[3] the BVG unified cosmology,[4] and the bilobular collision model,[5] remain under active research. None has so far displaced the standard ΛCDM model, which the Planck data fit well.[2]
The universe today
Expansion
The universe is expanding: on the largest scales, the distances between galaxies grow with time, and the more distant a galaxy is, the faster it recedes from us. In 1927, Georges Lemaître showed that general relativity admits a homogeneous universe of constant mass and increasing radius, and derived a linear relation between the distance of extra-galactic nebulae and their radial velocity.[6] In 1929, Edwin Hubble gave the relation its observational foundation, using distances to extra-galactic nebulae measured from the Cepheid variable stars they contain.[7] The relation, known today as the Hubble–Lemaître law (historically, Hubble's law), is characterised by the Hubble constant, H0, the present-day expansion rate; from the CMB, the Planck Collaboration measures H0 = (67.4 ± 0.5) km s−1 Mpc−1.[2]
Composition
In the standard model, the universe today consists of about 68% dark energy, about 27% dark matter, and about 5% ordinary (baryonic) matter.[2] Ordinary matter is the stuff of stars, planets, and gas; dark matter neither emits nor absorbs light and reveals itself only through its gravity, which binds galaxies and galaxy clusters;[8] and dark energy behaves like the cosmological constant of general relativity, driving the accelerated expansion of the universe in the standard model.[2]
Large-scale structure
Matter is not spread uniformly: gravity has gathered it into galaxies, groups, and clusters, which in turn form superclusters, walls, and filaments. On the very largest scales these structures arrange themselves into the cosmic web, a pattern of filaments and walls surrounding vast, nearly empty voids, which forms as gravitational attraction draws matter into ever larger concentrations.[8] Averaged over still larger scales, the universe is homogeneous and isotropic, an assumption built into the standard model of cosmology and consistent with Planck's measurements of the CMB.[2]
References
- ↑ Johnson, C. (2017). An Introduction to Geology. In An Introduction to Geology. OpenGeology.
- ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ Planck Collaboration. (2020). Planck 2018 results (Scholarly article). In Astronomy and Astrophysics (Vols. 641, p. A6). https://doi.org/10.1051/0004-6361/201833910
- ↑ Gunn, A. (2025). This bold theory says the Big Bang wasn’t our beginning. In BBC Science Focus.
- ↑ Varnam, B. (2026). The BVG Unified Cosmology: A Complete Field-Driven Alternative to the Big Bang. Zenodo. https://doi.org/10.5281/zenodo.20591798
- ↑ Aldana, A. D. (2026). The Origin of the Universe Without a Big Bang Singularity: The Bilobular Collision Model as a Cyclic Anisotropic Alternative to ΛCDM. Zenodo. https://doi.org/10.5281/zenodo.20487411
- ↑ Lemaître, G. (1927). Un univers homogène de masse constante et de rayon croissant rendant compte de la vitesse radiale des nébuleuses extra-galactiques (Scholarly article). In Annales de la Société scientifique de Bruxelles (Vols. 47, pp. 49–59).
- ↑ Hubble, E. (1929). A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae (Scholarly article). In Proceedings of the National Academy of Sciences of the United States of America (Vols. 15, Issues 3, pp. 168–173). https://doi.org/10.1073/pnas.15.3.168
- ↑ ↑ National Aeronautics and Space Administration. (n.d.). Large Scale Structures (Webpage). In NASA Science (Website).
Further reading
- The Universe, NASA Science
- Planck, European Space Agency