Editing Quantum cosmology (section)

{{Short description|Attempts to develop a quantum mechanical theory of cosmology}}
{{quantum field theory}}

'''Quantum cosmology'''<ref name="url[1501.04899] Quantum cosmology: a review">{{Cite journal|title=Quantum cosmology: A review |year=2015 |doi=10.1088/0034-4885/78/2/023901 |arxiv=1501.04899 |last1=Bojowald |first1=Martin |journal=Reports on Progress in Physics |volume=78 |issue=2 |page=023901 |pmid=25582917 |bibcode=2015RPPh...78b3901B |s2cid=18463042 }}</ref><ref name="url[1412.4362] Loop Quantum Gravity">{{Cite journal|title=Loop quantum gravity |year=2015 |doi=10.1142/S0218271815300050 |arxiv=1412.4362 |last1=Chiou |first1=Dah-Wei |journal=International Journal of Modern Physics D |volume=24 |issue=1 |pages=1530005–1530331 |bibcode=2015IJMPD..2430005C |s2cid=16655619 }}</ref> is the attempt in [[theoretical physics]] to develop a [[Quantum field theory|quantum theory]] of the [[universe]]. This approach attempts to answer open questions of classical [[physical cosmology]], particularly those related to the first phases of the universe.

Classical cosmology is based on [[Albert Einstein]]'s [[general theory of relativity]] (GTR or simply GR) which describes the evolution of the universe very well, as long as you do not approach the [[Big Bang]]. It is the [[gravitational singularity]] and the [[Planck time]] where relativity theory fails to provide what must be demanded of a final theory of space and time. Therefore, a theory is needed that integrates relativity theory and quantum theory.<ref>Stephen Hawking wrote 1999: ''So what the singularity theorems are really telling us, is that the universe had a quantum origin, and that we need a theory of quantum cosmology, if we are to predict the present state of the universe.''{{cite web |title=Quantum Cosmology, M-theory and the Anthropic Principle – Stephen Hawking |url=http://www.hawking.org.uk/quantum-cosmology-m-theory-and-the-anthropic-principle.html |url-status=dead |archive-url=https://web.archive.org/web/20150214222724/http://www.hawking.org.uk/quantum-cosmology-m-theory-and-the-anthropic-principle.html |archive-date=2015-02-14 |access-date=2015-02-14}}</ref> Such an approach is attempted for instance with [[loop quantum cosmology]], [[loop quantum gravity]], [[string theory]] and [[Causal sets|causal set theory]].<ref>{{cite journal|author=Klebanov, Igor |author2=Maldacena, Juan |name-list-style=amp |title=Solving Quantum Field Theories via Curved Spacetimes |journal=[[Physics Today]] |date=2009 |page=28 |doi=10.1063/1.3074260 |volume=62 |issue=1 |bibcode=2009PhT....62a..28K |doi-access=free }}</ref>

In quantum cosmology, the universe is treated as a [[wave function]] instead of classical [[spacetime]].<ref name="urlarxiv.org">{{Cite journal|arxiv=1404.1207 |doi=10.1103/PhysRevD.89.083510 |title=Spontaneous creation of the universe from nothing |year=2014 |last1=He |first1=Dongshan |last2=Gao |first2=Dongfeng |last3=Cai |first3=Qing-yu |journal=Physical Review D |volume=89 |issue=8 |page=083510 |bibcode=2014PhRvD..89h3510H |s2cid=118371273 }}</ref>