Editing Universe (section)

=== Shape ===
{{Main|Shape of the universe}}
[[File:End of universe.jpg|thumb|The three possible options for the shape of the universe]]

Cosmologists often work with [[space-like]] slices of spacetime that are surfaces of constant time in [[Comoving distance|comoving coordinates]]. The geometry of these spatial slices is set by the [[density parameter]], Omega (Ω), defined as the average matter density of the universe divided by a critical value. This selects one of three possible [[Shape of the universe|geometries]] depending on whether Ω is equal to, less than, or greater than 1. These are called, respectively, the flat, open and closed universes.<ref name=FateOfTheUniverse>{{cite web|title=What is the Ultimate Fate of the Universe?|url=http://map.gsfc.nasa.gov/universe/uni_fate.html|publisher=National Aeronautics and Space Administration |access-date=August 23, 2015|archive-date=December 22, 2021|archive-url=https://web.archive.org/web/20211222195155/https://map.gsfc.nasa.gov/universe/uni_fate.html|url-status=live}}</ref>

Observations, including the [[Cosmic Background Explorer]] (COBE), [[Wilkinson Microwave Anisotropy Probe]] (WMAP), and [[Planck (spacecraft)|Planck]] maps of the CMB, suggest that the universe is infinite in extent with a finite age, as described by the [[Friedmann–Lemaître–Robertson–Walker metric|Friedmann–Lemaître–Robertson–Walker]] (FLRW) models.<ref name="nasa_popular_uni_curv">{{Cite web |title=WMAP – Shape of the Universe |url=https://map.gsfc.nasa.gov/universe/uni_shape.html |access-date=February 14, 2023 |website=map.gsfc.nasa.gov |archive-date=March 31, 2019 |archive-url=https://web.archive.org/web/20190331105235/https://map.gsfc.nasa.gov/universe/uni_shape.html |url-status=live }}</ref><ref name="Nat03">{{cite journal
 |last1        = Luminet
 |first1       = Jean-Pierre
 |author-link  = Jean-Pierre Luminet
 |last2        = Weeks
 |first2       = Jeffrey R.
 |last3        = Riazuelo
 |first3       = Alain
 |last4        = Lehoucq
 |first4       = Roland
 |last5        = Uzan
 |first5       = Jean-Philippe
 |title        = Dodecahedral space topology as an explanation for weak wide-angle temperature correlations in the cosmic microwave background
 |journal      = [[Nature (journal)|Nature]]
 |volume       = 425
 |issue        = 6958
 |pages        = 593–595
 |date         = October 9, 2003
|pmid         = 14534579
 |arxiv        = astro-ph/0310253
 |doi          = 10.1038/nature01944
 |bibcode      = 2003Natur.425..593L
 |s2cid        = 4380713
 |url          = https://cds.cern.ch/record/647738
 |type         = Submitted manuscript
 |access-date  = August 21, 2018
|archive-date = May 17, 2021
|archive-url  = https://web.archive.org/web/20210517180259/https://cds.cern.ch/record/647738
 |url-status   = live
}}</ref><ref name="RBSG08">{{cite journal|last1=Roukema|first1=Boudewijn|first2=Zbigniew |last2=Buliński |first3=Agnieszka |last3=Szaniewska |first4=Nicolas E. |last4=Gaudin |title=A test of the Poincare dodecahedral space topology hypothesis with the WMAP CMB data|journal=Astronomy and Astrophysics|volume=482|issue=3 |pages=747–753|date=2008|arxiv=0801.0006|doi=10.1051/0004-6361:20078777|bibcode=2008A&A...482..747L|s2cid=1616362}}</ref><ref name="Aurich0403597">{{cite journal|last=Aurich|first=Ralf|author2=Lustig, S. |author3=Steiner, F. |author4=Then, H. |title=Hyperbolic Universes with a Horned Topology and the CMB Anisotropy|journal=Classical and Quantum Gravity|volume=21 |issue=21 |pages=4901–4926|date=2004 |doi=10.1088/0264-9381/21/21/010 |arxiv=astro-ph/0403597|bibcode=2004CQGra..21.4901A|s2cid=17619026}}</ref> These FLRW models thus support inflationary models and the standard model of cosmology, describing a [[Minkowski space|flat]], homogeneous universe presently dominated by [[dark matter]] and [[dark energy]].<ref name="planck_cosmological_parameters">{{cite journal |arxiv=1303.5076 |title=Planck 2013 results. XVI. Cosmological parameters |author=Planck Collaboration |journal=Astronomy & Astrophysics |date=2014 |bibcode=2014A&A...571A..16P |doi=10.1051/0004-6361/201321591 |volume=571 |page=A16|s2cid=118349591 }}</ref><ref>{{cite web
|title=Planck reveals 'almost perfect' universe
|url=http://physicsworld.com/cws/article/news/2013/mar/21/planck-reveals-almost-perfect-universe
|work=Michael Banks
|publisher=Physics World
|date=March 21, 2013
|access-date=March 21, 2013
|archive-date=March 24, 2013
|archive-url=https://web.archive.org/web/20130324022238/http://physicsworld.com/cws/article/news/2013/mar/21/planck-reveals-almost-perfect-universe
|url-status=live
}}</ref>