Quantum cosmology

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

{{quantum field theory}}

Quantum cosmology{{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 }}{{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 }} is the attempt in theoretical physics to develop a 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.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}} Such an approach is attempted for instance with loop quantum cosmology, loop quantum gravity, string theory and causal set theory.{{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 }}

In quantum cosmology, the universe is treated as a wave function instead of classical spacetime.{{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 }}