Lambda-CDM model: Difference between revisions

Revision as of 18:49, 3 February 2025

Revision as of 19:53, 3 February 2025

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The model assumes that [[general relativity]] is the correct theory of gravity on cosmological scales. It emerged in the late 1990s as a '''concordance cosmology''', after a period of time when disparate observed properties of the universe appeared mutually inconsistent, and there was no consensus on the makeup of the energy density of the universe.

The ΛCDM model has been successful in modeling broad collection of astronomical observations over decades. Remaining issues have lead to many alternative models and challenges the assumptions of the ΛCDM model.<ref name="Snowmass21"/>

== Overview ==

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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 |last=Davis |first=Tamara M. |last2=Lineweaver |first2=Charles H. |date=January 2004-01 |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}}</ref>

== Cosmic expansion history ==

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|url=https://www.livescience.com/hubble-constant-discrepancy-explained.html

|date=26 August 2019 |work=[[Live Science]] |access-date=26 August 2019

}}</ref><ref name="Snowmass21"/><ref name="Turner"/>

Dozens of proposals for modifications of ΛCDM or completely new models have been published to explain the Hubble tension. Among these models are many that modify the properties of [[dark energy]] or of [[dark matter]] over time, interactions between dark energy and dark matter, unified dark energy and matter, other forms of dark radiation like [[sterile neutrinos]], modifications to the properties of gravity, or the modification of the effects of [[inflation (cosmology)|inflation]], changes to the properties of elementary particles in the early universe, among others. None of these models can simultaneously explain the breadth of other cosmological data as well as ΛCDM.<ref name="di Valentino 2021 153001"/>

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Several discrepancies between the predictions of [[cold dark matter]] in the ΛCDM model and observations of galaxies and their clustering have arisen. Some of these problems have proposed solutions, but it remains unclear whether they can be solved without abandoning the ΛCDM model.<ref>{{Cite journal |arxiv=1006.1647 |title=Local-Group tests of dark-matter Concordance Cosmology: Towards a new paradigm for structure formation |year=2010 |last1=Kroupa |first1=P. |last2=Famaey |first2=B. |last3=de Boer |first3=Klaas S. |last4=Dabringhausen |first4=Joerg |last5=Pawlowski |first5=Marcel |last6=Boily |first6=Christian |last7=Jerjen |first7=Helmut |last8=Forbes |first8=Duncan |last9=Hensler |first9=Gerhard |journal=Astronomy and Astrophysics |volume=523 |pages=32–54 |doi=10.1051/0004-6361/201014892 |bibcode=2010A&A...523A..32K|s2cid=11711780 }}</ref>

[[Mordehai Milgrom|Milgrom]], [[Stacy McGaugh|McGaugh]], and [[Pavel Kroupa|Kroupa]] have criticized the dark matter portions of the theory from the perspective of [[galaxy formation]] models and supporting the alternative [[modified Newtonian dynamics]] (MOND) theory, which requires a modification of the [[Einstein field equations]] and the [[Friedmann equations]] as seen in proposals such as [[modified gravity theory]] (MOG theory) or [[tensor–vector–scalar gravity]] theory (TeVeS theory).{{cncitation needed|date=January 2025}} Other proposals by theoretical astrophysicists of cosmological alternatives to Einstein's general relativity that attempt to account for dark energy or dark matter include [[f(R) gravity]], [[Scalar–tensor theory|scalar–tensor theories]] such as {{ill|galileon|ko}} theories (see [[Galilean invariance]]), [[brane cosmology|brane cosmologies]], the [[DGP model]], and [[massive gravity]] and its extensions such as [[bimetric theory|bimetric gravity]].{{citation needed|date=February 2024}}

==== Cuspy halo problem ====