Lambda-CDM model: Difference between revisions

Revision as of 02:23, 19 June 2025

Revision as of 21:56, 18 July 2025

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* Cold: Its velocity is far less than the speed of light at the epoch of radiation–matter equality (thus neutrinos are excluded, being non-baryonic but not cold)

* Dissipationless: Cannot cool by radiating photons

* Collisionless: Dark matter particles interact with each other and other particles only through gravity and possibly the [[weak force]]

Dark matter constitutes about 26.5%<ref name="PDG2019">{{cite journal |first1=M. |last1= Tanabashi |display-authors=etal |collaboration=[[Particle Data Group]] |url=http://pdg.lbl.gov/2019/reviews/rpp2019-rev-astrophysical-constants.pdf |title=Astrophysical Constants and Parameters |publisher=[[Particle Data Group]] |year=2019 |access-date=2020-03-08 |journal=Physical Review D |volume=98 |issue=3 |page=030001|doi= 10.1103/PhysRevD.98.030001|doi-access=free |bibcode= 2018PhRvD..98c0001T }}</ref> of the mass–energy density of the universe. The remaining 4.9%<ref name="PDG2019"/> comprises all ordinary matter observed as atoms, chemical elements, gas and [[Plasma (physics)|plasma]], the stuff of which visible planets, stars and galaxies are made. The great majority of ordinary matter in the universe is unseen, since visible stars and gas inside galaxies and clusters account for less than 10% of the ordinary matter contribution to the mass–energy density of the universe.<ref>

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The model includes a single originating event, the "[[Big Bang]]", which was not an explosion but the abrupt appearance of expanding [[spacetime]] containing radiation at temperatures of around 10¹⁵&nbsp;K. This was immediately (within 10⁻²⁹ seconds) followed by an exponential expansion of space by a scale multiplier of 10²⁷ or more, known as [[cosmic inflation]]. The early universe remained hot (above 10 ,000 K) for several hundred thousand years, a state that is detectable as a residual [[cosmic microwave background]], or CMB, a very low-energy radiation emanating from all parts of the sky. The "Big Bang" scenario, with cosmic inflation and standard particle physics, is the only cosmological model consistent with the observed continuing expansion of space, the observed distribution of [[Big Bang nucleosynthesis|lighter elements in the universe]] (hydrogen, helium, and lithium), and the spatial texture of minute irregularities ([[Anisotropy|anisotropies]]) in the CMB radiation. Cosmic inflation also addresses the "[[horizon problem]]" in the CMB; indeed, it seems likely that the universe is larger than the observable [[particle horizon]].<ref>{{Cite journal |last1=Davis |first1=Tamara M. |last2=Lineweaver |first2=Charles H. |date=January 2004 |title=Expanding Confusion: Common Misconceptions of Cosmological Horizons and the Superluminal Expansion of the Universe |url=https://www.cambridge.org/core/journals/publications-of-the-astronomical-society-of-australia/article/expanding-confusion-common-misconceptions-of-cosmological-horizons-and-the-superluminal-expansion-of-the-universe/EFEEEFD8D71E59F86DDA82FDF576EFD3 |journal=Publications of the Astronomical Society of Australia |language=en |volume=21 |issue=1 |pages=97–109 |doi=10.1071/AS03040 |issn=1323-3580|arxiv=astro-ph/0310808 |bibcode=2004PASA...21...97D }}</ref>

== Cosmic expansion history ==