Editing Physical cosmology (section)

===Very early universe===
[[File:Big bang inflation vs standard genericchart.png|thumb|upright=1.2|The inflationary theory as an augmentation to the Big Bang theory was first proposed by Alan Guth of MIT. Inflation solves the 'horizon problem' by making the early universe much more compact than was assumed in the standard model. Given such smaller size, causal contact (i.e., thermal communication) would have been possible among all regions of the early universe. The image was an adaptation from various generic charts depicting the growth of the size of the observable universe, for both the standard model and inflationary model respectively, of the Big Bang theory.]]
The early, hot universe appears to be well explained by the Big Bang from roughly 10<sup>−33</sup> seconds onwards, but there are several [[Big Bang#Problems|problems]]. One is that there is no compelling reason, using current particle physics, for the universe to be [[shape of the universe|flat]], homogeneous, and [[isotropic]] ''(see the [[cosmological principle]])''. Moreover, [[grand unified theory|grand unified theories]] of particle physics suggest that there should be [[magnetic monopole]]s in the universe, which have not been found. These problems are resolved by a brief period of [[cosmic inflation]], which drives the universe to [[Flatness (cosmology)|flatness]], smooths out [[Anisotropy|anisotropies]] and inhomogeneities to the observed level, and exponentially dilutes the monopoles.<ref name=Guth1981>{{cite journal | title=Inflationary universe: A possible solution to the horizon and flatness problems | last1=Guth | first1=Alan H. | journal=Physical Review D | volume=23 | issue=2 | date=15 January 1981 | pages=347–356 | doi=10.1103/PhysRevD.23.347 | bibcode=1981PhRvD..23..347G | doi-access=free }}</ref> The physical model behind cosmic inflation is extremely simple, but it has not yet been confirmed by particle physics, and there are difficult problems reconciling inflation and [[quantum field theory]].{{Vague|date=April 2018}} Some cosmologists think that [[string theory]] and [[brane cosmology]] will provide an alternative to inflation.<ref name=Pogosian2003>{{cite journal | title=Observational constraints on cosmic string production during brane inflation | last1=Pogosian | first1=Levon | last2=Tye | first2=S.-H. Henry | last3=Wasserman | first3=Ira | last4=Wyman | first4=Mark | journal=Physical Review D | volume=68 | issue=2 | page=023506 | year=2003 | doi=10.1103/PhysRevD.68.023506 | bibcode=2003PhRvD..68b3506P | arxiv=hep-th/0304188 }}</ref>

Another major problem in cosmology is what caused the universe to contain far more matter than [[antimatter]]. Cosmologists can observationally deduce that the universe is not split into regions of matter and antimatter. If it were, there would be [[X-ray]]s and [[gamma ray]]s produced as a result of [[annihilation]], but this is not observed. Therefore, some process in the early universe must have created a small excess of matter over antimatter, and this (currently not understood) process is called ''[[baryogenesis]]''. Three required conditions for baryogenesis were derived by [[Andrei Sakharov]] in 1967, and requires a violation of the particle physics [[Symmetry#In physics|symmetry]], called [[CP-symmetry]], between matter and antimatter.<ref name=Canetti2012>{{cite journal | title=Matter and antimatter in the universe | display-authors=1 | first1=Laurent | last1=Canetti | first2=Marco | last2=Drewes | first3=Mikhail | last3=Shaposhnikov | journal=New Journal of Physics | volume=14 | issue=9 | pages=095012 | date=September 2012 | doi=10.1088/1367-2630/14/9/095012 | bibcode=2012NJPh...14i5012C | arxiv=1204.4186 | s2cid=119233888 }}</ref> However, particle accelerators measure too small a violation of CP-symmetry to account for the baryon asymmetry. Cosmologists and particle physicists look for additional violations of the CP-symmetry in the early universe that might account for the [[baryon asymmetry]].<ref name=Pandolfi2017>{{cite web | title=New source of asymmetry between matter and antimatter | first1=Stefania | last1=Pandolfi | date=30 January 2017 | publisher=CERN | url=https://home.cern/about/updates/2017/01/new-source-asymmetry-between-matter-and-antimatter | access-date=2018-04-09 }}</ref>

Both the problems of baryogenesis and cosmic inflation are very closely related to particle physics, and their resolution might come from high energy theory and [[particle accelerator|experiment]], rather than through observations of the universe.{{speculation inline|date=April 2018}}<!-- This statement is both speculative and somewhat obvious. It will either be one, the other, or none. Is it needed? -->