Universe

== Definition ==
[[File:NASA-HubbleLegacyFieldZoomOut-20190502.webm|thumb|upright=2.7|center|<div align="center">[[Hubble Space Telescope]] – [[Hubble Ultra-Deep Field|Ultra-Deep Field galaxies]] to Legacy field zoom out<br />(video 00:50; May 2, 2019)</div>]]
The physical universe is defined as all of [[space]] and [[time]]{{efn|name=spacetime|}} (collectively referred to as [[spacetime]]) and their contents.<ref name="Zeilik1998" /> Such contents comprise all of energy in its various forms, including [[electromagnetic radiation]] and [[matter]], and therefore planets, [[natural satellite|moons]], stars, galaxies, and the contents of [[intergalactic space]].<ref name="Britannica">{{cite encyclopedia |title=Universe |encyclopedia=Encyclopaedia Britannica online |date=2012 |url=https://www.britannica.com/science/universe |access-date=February 17, 2018 |archive-date=June 9, 2021 |archive-url=https://web.archive.org/web/20210609004717/https://www.britannica.com/science/universe |url-status=live }}</ref><ref>{{cite web |url=http://www.merriam-webster.com/dictionary/Universe |title=Universe |work=Merriam-Webster Dictionary |access-date=September 21, 2012 |archive-date=October 22, 2012 |archive-url=https://web.archive.org/web/20121022182145/http://www.merriam-webster.com/dictionary/universe |url-status=live }}</ref><ref>{{cite web |url=http://dictionary.reference.com/browse/Universe?s=t |title=Universe |work=Dictionary.com |access-date=September 21, 2012 |archive-date=October 23, 2012 |archive-url=https://web.archive.org/web/20121023004855/http://dictionary.reference.com/browse/universe?s=t |url-status=live }}</ref> The universe also includes the [[physical law]]s that influence energy and matter, such as [[conservation law]]s, [[classical mechanics]], and [[Theory of relativity|relativity]].<ref name="Schreuder2014">{{cite book|first=Duco A.|last=Schreuder|title=Vision and Visual Perception|url=https://books.google.com/books?id=I7a7BQAAQBAJ&pg=PA135|date=2014|publisher=Archway Publishing|isbn=978-1-4808-1294-9|page=135|access-date=January 27, 2016|archive-date=April 22, 2021|archive-url=https://web.archive.org/web/20210422045606/https://books.google.com/books?id=I7a7BQAAQBAJ&pg=PA135|url-status=live}}</ref>

The universe is often defined as "the totality of existence", or [[everything]] that exists, everything that has existed, and everything that will exist.<ref name="Schreuder2014" /> In fact, some philosophers and scientists support the inclusion of ideas and abstract concepts—such as mathematics and logic—in the definition of the universe.{{refn|1={{cite journal |last=Tegmark |first=Max |title=The Mathematical Universe |journal=Foundations of Physics |volume=38 |issue=2 |pages=101–150 |doi=10.1007/s10701-007-9186-9 |bibcode=2008FoPh...38..101T |arxiv=0704.0646 |year=2008|s2cid=9890455 }} A short version of which is available at {{cite arXiv |eprint=0709.4024 |title=Shut up and calculate|last1=Fixsen|first1=D. J.|class=physics.pop-ph|year=2007}} in reference to David Mermin's famous quote "shut up and calculate!"<ref>{{cite journal |title=Could Feynman Have Said This? |first=N. David |last=Mermin |journal=Physics Today |volume=57 |issue=5 |page=10 |date=2004 |doi=10.1063/1.1768652 |bibcode=2004PhT....57e..10M |doi-access= }}</ref>}}<ref>{{cite book|first=Jim|last=Holt|title=Why Does the World Exist?|publisher=Liveright Publishing |year=2012|page=308}}</ref><ref>{{cite book|first=Timothy|last=Ferris|title=The Whole Shebang: A State-of-the-Universe(s) Report|publisher=Simon & Schuster|year=1997|page=400}}</ref> The word ''universe'' may also refer to concepts such as ''the cosmos'', ''the world'', and ''nature''.<ref>{{cite book |title=Creation Out of Nothing: A Biblical, Philosophical, and Scientific Exploration |page=[https://archive.org/details/creationoutofnot0000copa/page/220 220] |first1=Paul |last1=Copan |author2=William Lane Craig |publisher=Baker Academic |date=2004 |isbn=978-0-8010-2733-8 |url=https://archive.org/details/creationoutofnot0000copa/page/220 }}</ref><ref name="Bolonkin2011">{{cite book|first=Alexander|last=Bolonkin|title=Universe, Human Immortality and Future Human Evaluation|url=https://books.google.com/books?id=TuWQx58ZnPsC&pg=PA3|date=2011|publisher=Elsevier|isbn=978-0-12-415801-6|pages=3–|access-date=January 27, 2016|archive-date=February 8, 2021|archive-url=https://web.archive.org/web/20210208114300/https://books.google.com/books?id=TuWQx58ZnPsC&pg=PA3|url-status=live}}</ref>