Editing Big Bang (section)

===Dark matter===
{{Main|Dark matter}}
[[File:Cosmological Composition – Pie Chart.svg|thumb|right|upright=1.6|[[pie chart|Chart]] shows the proportion of different components of the universe {{spaced ndash}} about 95% is [[dark matter]] and [[dark energy]].]]
During the 1970s and the 1980s, various observations showed that there is not sufficient visible matter in the universe to account for the apparent strength of gravitational forces within and between galaxies. This led to the idea that up to 90% of the matter in the universe is dark matter that does not emit light or interact with normal baryonic matter. In addition, the assumption that the universe is mostly normal matter led to predictions that were strongly inconsistent with observations. In particular, the universe today is far more lumpy and contains far less deuterium than can be accounted for without dark matter. While dark matter has always been controversial, it is inferred by various observations: the anisotropies in the CMB, the [[galaxy rotation problem]], [[galaxy cluster]] [[velocity dispersion]]s, large-scale structure distributions, [[gravitational lens]]ing studies, and [[X-ray astronomy|X-ray measurements]] of galaxy clusters.<ref>{{cite web |url=http://pages.astronomy.ua.edu/keel/galaxies/darkmatter.html |url-status=live |last=Keel |first=William C. |date=October 2009 |orig-date=Last changes: February 2015 |title=Dark Matter |website=Bill Keel's Lecture Notes – Galaxies and the Universe |archive-url=https://web.archive.org/web/20190503112916/http://pages.astronomy.ua.edu/keel/galaxies/darkmatter.html |archive-date=3 May 2019 |access-date=15 December 2019}}</ref>

Indirect evidence for dark matter comes from its gravitational influence on other matter, as no dark matter particles have been observed in laboratories. Many particle physics candidates for dark matter have been proposed, and several projects to detect them directly are underway.<ref name="pdg">{{harvnb|Tanabashi, M.|2018|pp=[http://pdg.lbl.gov/2018/reviews/rpp2018-rev-dark-matter.pdf 396–405]|loc=chpt. 26: "Dark Matter" (Revised September 2017) by Manuel Drees and Gilles Gerbier.}}
* {{harvnb|Yao, W.-M.|2006|pp=[http://pdg.lbl.gov/2006/reviews/darkmatrpp.pdf 233–237]|loc=chpt. 22: "Dark Matter" (September 2003) by Manuel Drees and Gilles Gerbier.}}</ref>

Additionally, there are outstanding problems associated with the currently favored cold dark matter model which include the [[dwarf galaxy problem]]<ref name="Martínez-Delgado">{{Cite book |arxiv= 1009.4505|last1 = Bullock|first1 = James S.|title = Local Group Cosmology|chapter= Notes on the Missing Satellites Problem |pages = 95–122|year = 2010 |doi=10.1017/CBO9781139152303.004|isbn = 9781139152303|s2cid = 119270708|editor1-last = Martinez-Delgado|editor1-first = David|editor2-last = Mediavilla|editor2-first = Evencio}}</ref> and the [[cuspy halo problem]].<ref name="Diemand2005">{{cite journal |last1=Diemand |first1=Jürg |last2=Zemp |first2=Marcel |last3=Moore |first3=Ben |last4=Stadel |first4=Joachim |last5=Carollo |first5=C. Marcella |author-link5=C. Marcella Carollo |date=December 2005 |title=Cusps in cold dark matter haloes |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=364 |issue=2 |pages=665–673 |arxiv=astro-ph/0504215 |bibcode=2005MNRAS.364..665D |doi=10.1111/j.1365-2966.2005.09601.x |doi-access=free |s2cid=117769706 }}</ref> Alternative theories have been proposed that do not require a large amount of undetected matter, but instead modify the laws of gravity established by Newton and Einstein; yet no alternative theory has been as successful as the cold dark matter proposal in explaining all extant observations.<ref>{{cite journal |last1=Dodelson |first1=Scott |date=31 December 2011 |title=The Real Problem with MOND |journal=[[International Journal of Modern Physics D]] |arxiv=1112.1320 |doi=10.1142/S0218271811020561 |volume=20 |issue=14 |pages=2749–2753 |bibcode=2011IJMPD..20.2749D |s2cid=119194106 }}</ref>