Editing Physical cosmology (section)

===Big Bang Theory===
{{Main|Big Bang nucleosynthesis}}
Big Bang nucleosynthesis is the theory of the formation of the elements in the early universe. It finished when the universe was about three minutes old and its [[temperature]] dropped below that at which [[nuclear fusion]] could occur. Big Bang nucleosynthesis had a brief period during which it could operate, so only the very lightest elements were produced. Starting from hydrogen [[ion]]s ([[proton]]s), it principally produced [[deuterium]], [[helium|helium-4]], and [[lithium]]. Other elements were produced in only trace abundances. The basic theory of nucleosynthesis was developed in 1948 by George Gamow, [[Ralph Asher Alpher]], and [[Robert Herman]].<ref name=Peebles2014>{{cite journal | title=Discovery of the hot Big Bang: What happened in 1948 | last1=Peebles | first1=Phillip James Edwin | journal=The European Physical Journal H | volume=39 | issue=2 | pages=205–223 | date=April 2014 | doi=10.1140/epjh/e2014-50002-y | bibcode=2014EPJH...39..205P | arxiv=1310.2146 | s2cid=118539956 }}</ref> It was used for many years as a probe of physics at the time of the Big Bang, as the theory of Big Bang nucleosynthesis connects the abundances of primordial light elements with the features of the early universe.<ref name=Burles2001>{{cite journal | title=Big Bang Nucleosynthesis Predictions for Precision Cosmology | last1=Burles | first1=Scott | last2=Nollett | first2=Kenneth M. | last3=Turner | first3=Michael S. | journal=The Astrophysical Journal | volume=552 | issue=1 | pages=L1–L5 | date=May 2001 | doi=10.1086/320251 | bibcode=2001ApJ...552L...1B | arxiv=astro-ph/0010171 | s2cid=118904816 }}</ref> Specifically, it can be used to test the [[equivalence principle]],<ref name=Boucher2004>{{cite journal | title=Cosmic microwave background constraints on the strong equivalence principle | last1=Boucher | first1=V. | last2=Gérard | first2=J.-M. | last3=Vandergheynst | first3=P. | last4=Wiaux | first4=Y. | journal=Physical Review D | volume=70 | issue=10 | page=103528 | date=November 2004 | doi=10.1103/PhysRevD.70.103528 | bibcode=2004PhRvD..70j3528B | arxiv=astro-ph/0407208 | s2cid=1197376 }}</ref> to probe [[dark matter]], and test [[neutrino]] physics.<ref name=Cyburt2016>{{cite journal | title=Big bang nucleosynthesis: Present status | last1=Cyburt | first1=Richard H. | last2=Fields | first2=Brian D. | last3=Olive | first3=Keith A. | last4=Yeh | first4=Tsung-Han | journal=Reviews of Modern Physics | volume=88 | issue=1 | page=015004 | date=January 2016 | doi=10.1103/RevModPhys.88.015004 | bibcode=2016RvMP...88a5004C | arxiv=1505.01076 | s2cid=118409603}}</ref> Some cosmologists have proposed that Big Bang nucleosynthesis suggests there is a fourth "sterile" species of neutrino.<ref name=Lucente2018>{{cite arXiv| title=Leptogenesis, dark matter and neutrino masses | last1=Lucente | first1=Michele | last2=Abada | first2=Asmaa | last3=Arcadi | first3=Giorgio | last4=Domcke | first4=Valerie  | eprint=1803.10826 | date=March 2018| class=hep-ph }}</ref>

====Standard model of Big Bang cosmology====
The '''ΛCDM''' ('''Lambda cold dark matter''') or '''[[Lambda-CDM]]''' model is a [[Parametric equation|parametrization]] of the Big Bang cosmological model in which the universe contains a cosmological constant, denoted by [[Lambda]] ([[Greek alphabet|Greek]] '''Λ'''), associated with dark energy, and [[cold dark matter]] (abbreviated '''CDM'''). It is frequently referred to as the '''standard model''' of Big Bang cosmology.<ref name=Planck2015>{{cite journal | title=Planck 2015 Results. XIII. Cosmological Parameters | arxiv=1502.01589 | last1=Collaboration | first1=Planck | last2=Ade | first2=P. A. R. | last3=Aghanim | first3=N.|author3-link=Nabila Aghanim | last4=Arnaud | first4=M. | last5=Ashdown | first5=M. |last6=Aumont  | first6=J. | last7=Baccigalupi | first7=C. | last8=Banday | first8=A. J. | last9=Barreiro | first9=R. B. | last10=Bartlett | first10=J. G. | last11=Bartolo | first11=N. | last12=Battaner | first12=E. | last13=Battye | first13=R. | last14=Benabed | first14=K. | last15=Benoit | first15=A. | last16=Benoit-Levy | first16=A. | last17=Bernard | first17=J. -P. | last18=Bersanelli | first18=M.  | last19=Bielewicz | first19=P. | last20=Bonaldi | first20=A. | last21=Bonavera | first21=L. | last22=Bond | first22=J. R. | last23=Borrill | first23=J. | last24=Bouchet | first24=F. R. | last25=Boulanger | first25=F. | last26=Bucher | first26=M. | last27=Burigana | first27=C. | last28=Butler | first28=R. C. | last29=Calabrese | first29=E. | last30=Cardoso | first30=J.-F. | display-authors=29 | year=2016 | doi=10.1051/0004-6361/201525830 | volume=594 | issue=13 | journal=Astronomy & Astrophysics | page=A13 | bibcode=2016A&A...594A..13P | s2cid=119262962 }}</ref><ref name=Carlisle>{{cite journal | title=Planck Upholds Standard Cosmology | first1=Camille M. | last1=Carlisle  | journal=Sky and Telescope | date=10 February 2015 | volume=130 | issue=1 | page=28 | publisher=Sky & Telescope Media | bibcode=2015S&T...130a..28C | url=http://www.skyandtelescope.com/astronomy-news/planck-upholds-standard-cosmology-0210201523/ | access-date=2018-04-09 }}</ref>