Editing Big Bang (section)

=== Singularity ===
{{see also|Gravitational singularity|Initial singularity|Planck units#Cosmology}}
Existing theories of physics cannot tell us about the moment of the Big Bang.<ref name="Chow-2008"/>
Extrapolation of the expansion of the universe backwards in time using only general relativity yields a [[gravitational singularity]] with [[Infinity#Physics|infinite]] [[density]] and [[temperature]] at a finite time in the past,<ref name=Hawking_Ellis_1973>{{harvnb|Hawking|Ellis|1973}}</ref> but the meaning of this extrapolation in the context of the Big Bang is unclear.<ref>{{Cite journal |last=Senovilla |first=José M. M. |date=May 1998 |title=Singularity Theorems and Their Consequences |url=http://link.springer.com/10.1023/A:1018801101244 |journal=General Relativity and Gravitation |language=en |volume=30 |issue=5 |pages=701–848 |doi=10.1023/A:1018801101244 |arxiv=1801.04912 |bibcode=1998GReGr..30..701S |issn=0001-7701}}</ref> Moreover, [[classical field theory|classical]] gravitational theories are expected to be inadequate to describe physics under these conditions.<ref name="Peacock-1998">{{Cite book |last=Peacock |first=J. A. |url=https://www.cambridge.org/core/product/identifier/9780511804533/type/book |title=Cosmological Physics |date=1998-12-28 |publisher=Cambridge University Press |isbn=978-0-521-41072-4 |edition=1 |doi=10.1017/cbo9780511804533}}</ref>{{rp|275}} [[Quantum gravity]] effects are expected to be dominant during the [[Planck epoch]], when the temperature of the universe was close to the [[Planck scale]] (around 10<sup>32</sup> K or 10<sup>28</sup> eV).

Even below the Planck scale, undiscovered physics could greatly influence the expansion history of the universe. The Standard Model of particle physics is only tested up to temperatures of order 10<sup>17</sup>K (10 TeV) in particle colliders, such as the [[Large Hadron Collider]]. Moreover, new physical phenomena decoupled from the Standard Model could have been important before the time of [[neutrino decoupling]], when the temperature of the universe was only about 10<sup>10</sup>K (1 MeV).<ref>{{cite journal |last1=Allahverdi |first1=Rouzbeh |display-authors=et al |title=The first three seconds: A Review of Possible Expansion Histories of the early Universe |journal=The Open Journal of Astrophysics |date=29 January 2021 |volume=4 |issue=1 |page=1 |doi=10.21105/astro.2006.16182|arxiv=2006.16182 |bibcode=2021OJAp....4E...1A }}</ref>