Lambda-CDM model: Difference between revisions

Revision as of 09:54, 14 May 2025

Revision as of 16:56, 26 May 2025

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Finally, the light which will become astronomical observations must pass through the universe. The latter part of that journey will pass through [[reionization|ionized space]], where the electrons can scatter the light, altering the anisotropies. This effect is characterized by one additional parameter.<ref name=PDG-2024/>{{rp|25.1.3}}

The ΛCDM model includes an expansion of the spatial [[metricMetric spacetensor (general relativity)|metric]] that is well documented, both as the [[redshift]] of prominent spectral absorption or emission lines in the light from distant galaxies, and as the time dilation in the light decay of supernova luminosity curves. Both effects are attributed to a [[Doppler shift]] in electromagnetic radiation as it travels across expanding space. Although this expansion increases the distance between objects that are not under shared gravitational influence, it does not increase the size of the objects (e.g. galaxies) in space. Also, since it originates from ordinary general relativity, it, like general relativity, allows for distant galaxies to recede from each other at speeds greater than the speed of light; local expansion is less than the speed of light, but expansion summed across great distances can collectively exceed the speed of light.<ref name=DavisLineweaver>{{Cite journal |last1=Davis |first1=Tamara M. |last2=Lineweaver |first2=Charles H. |date=2004 |title=Expanding Confusion: Common Misconceptions of Cosmological Horizons and the Superluminal Expansion of the Universe |url=https://www.cambridge.org/core/product/identifier/S132335800000607X/type/journal_article |journal=Publications of the Astronomical Society of Australia |language=en |volume=21 |issue=1 |pages=97–109 |doi=10.1071/AS03040 |arxiv=astro-ph/0310808 |bibcode=2004PASA...21...97D |issn=1323-3580}}</ref>

The letter Λ ([[lambda]]) represents the [[cosmological constant]], which is associated with a vacuum energy or [[dark energy]] in empty space that is used to explain the contemporary accelerating expansion of space against the attractive effects of gravity. A cosmological constant has negative pressure, <math> p = - \rho c^{2} </math>, which contributes to the [[stress–energy tensor]] that, according to the general theory of relativity, causes accelerating expansion. The fraction of the total energy density of our (flat or almost flat) universe that is dark energy, <math>\Omega_{\Lambda}</math>, is estimated to be 0.669 ± 0.038 based on the 2018 [[Dark Energy Survey]] results using [[Type Ia supernova]]e<ref>{{Cite journal |arxiv = 1811.02374|author=DES Collaboration |title = First Cosmology Results using Type Ia Supernovae from the Dark Energy Survey: Constraints on Cosmological Parameters|journal = The Astrophysical Journal|volume = 872|issue = 2|pages = L30|year = 2018|doi = 10.3847/2041-8213/ab04fa|s2cid = 84833144 |doi-access=free |bibcode=2019ApJ...872L..30A }}</ref> or {{val|0.6847|0.0073}} based on the 2018 release of [[Planck (spacecraft)|''Planck'' satellite]] data, or more than 68.3% (2018 estimate) of the mass–energy density of the universe.<ref>{{Cite journal |arxiv = 1807.06209|author=Planck Collaboration|title = Planck 2018 results. VI. Cosmological parameters|journal = Astronomy & Astrophysics|year = 2020|volume = 641|pages = A6|doi = 10.1051/0004-6361/201833910|bibcode = 2020A&A...641A...6P|s2cid = 119335614}}</ref>