Universe

== Historical conceptions ==
{{See also|Cosmology|Timeline of cosmological theories|Nicolaus Copernicus#Copernican system|Philosophiæ Naturalis Principia Mathematica#Beginnings of the Scientific Revolution}}
Historically, there have been many ideas of the cosmos (cosmologies) and its origin (cosmogonies). Theories of an impersonal universe governed by physical laws were first proposed by the Greeks and Indians.<ref name=Routledge /> Ancient Chinese philosophy encompassed the notion of the universe including both all of space and all of time.<ref>{{cite news|last=Gernet|first=J.|date=1993–1994|title=Space and time: Science and religion in the encounter between China and Europe|journal=Chinese Science|volume=11|pages=93–102}}</ref> Over the centuries, improvements in astronomical observations and theories of motion and gravitation led to ever more accurate descriptions of the universe. The modern era of cosmology began with [[Albert Einstein]]'s 1915 [[general relativity|general theory of relativity]], which made it possible to quantitatively predict the origin, evolution, and conclusion of the universe as a whole. Most modern, accepted theories of cosmology are based on general relativity and, more specifically, the predicted [[Big Bang]].<ref name="Blandford">{{cite journal|title=A century of general relativity: Astrophysics and cosmology|author=Blandford R. D.|journal=Science|volume=347|issue=6226|pages=1103–1108|doi=10.1126/science.aaa4033|bibcode=2015Sci...347.1103B|pmid=25745165|year=2015|s2cid=30364122}}</ref>

=== Mythologies ===
{{Main|Creation myth|Cosmogony|Religious cosmology}}
Many cultures have [[List of creation myths|stories describing the origin of the world and universe]]. Cultures generally regard these stories as having some [[truth]]. There are however many differing beliefs in how these stories apply amongst those believing in a supernatural origin, ranging from a god directly creating the universe as it is now to a god just setting the "wheels in motion" (for example via mechanisms such as the big bang and evolution).<ref>{{cite book |quote="In common usage the word 'myth' refers to narratives or beliefs that are untrue or merely fanciful; the stories that make up national or ethnic mythologies describe characters and events that common sense and experience tell us are impossible. Nevertheless, all cultures celebrate such myths and attribute to them various degrees of literal or symbolic ''truth''." |last=Leeming |first=David A. |isbn=978-1-59884-174-9 |date=2010|page=xvii |title=Creation Myths of the World |publisher=ABC-CLIO}}</ref>

Ethnologists and anthropologists who study myths have developed various classification schemes for the various themes that appear in creation stories.<ref name=Eliade1964>{{cite book|last1=Eliade|first1=Mircea|title=Myth and Reality (Religious Traditions of the World)|date=1964|publisher=Allen & Unwin|isbn=978-0-04-291001-7}}</ref><ref name=Leonard2004>{{cite book|last1=Leonard|first1=Scott A.|last2=McClure|first2=Michael|title=Myth and Knowing: An Introduction to World Mythology|date=2004|publisher=McGraw-Hill|isbn=978-0-7674-1957-4|edition=}}</ref> For example, in one type of story, the world is born from a [[world egg]]; such stories include the [[Finnish people|Finnish]] [[epic poetry|epic poem]] ''[[Kalevala]]'', the [[China|Chinese]] story of [[Pangu]] or the [[History of India|Indian]] [[Brahmanda Purana]]. In related stories, the universe is created by a single entity emanating or producing something by him- or herself, as in the [[Tibetan Buddhism]] concept of [[Adi-Buddha]], the [[ancient Greece|ancient Greek]] story of [[Gaia (mythology)|Gaia]] (Mother Earth), the [[Aztec mythology|Aztec]] goddess [[Coatlicue]] myth, the [[ancient Egyptian religion|ancient Egyptian]] [[Ennead|god]] [[Atum]] story, and the [[Judeo-Christian]] [[Genesis creation narrative]] in which the [[God in Abrahamic religions|Abrahamic God]] created the universe. In another type of story, the universe is created from the union of male and female deities, as in the [[Maori mythology|Maori story]] of [[Rangi and Papa]]. In other stories, the universe is created by crafting it from pre-existing materials, such as the corpse of a dead god—as from [[Tiamat]] in the [[Babylon]]ian epic ''[[Enuma Elish]]'' or from the giant [[Ymir]] in [[Norse mythology]]—or from chaotic materials, as in [[Izanagi]] and [[Izanami]] in [[Japanese mythology]]. In other stories, the universe emanates from fundamental principles, such as [[Brahman]] and [[Prakrti]], the [[Serer creation myth|creation myth]] of the [[Serer people|Serers]],<ref>([[Henry Gravrand]], "La civilisation Sereer -Pangool") [in] [[Universität Frankfurt am Main]], Frobenius-Institut, Deutsche Gesellschaft für Kulturmorphologie, Frobenius Gesellschaft, "Paideuma: Mitteilungen zur Kulturkunde, Volumes 43–44", F. Steiner (1997), pp. 144–145, {{ISBN|3-515-02842-0}}</ref> or the [[yin and yang]] of the [[Tao]].

=== Philosophical models ===
{{Further|Cosmology}}
{{See also|Pre-Socratic philosophy|Physics (Aristotle)|Hindu cosmology|Islamic cosmology|Philosophy of space and time}}
The [[pre-Socratic philosophy|pre-Socratic Greek philosophers]] and Indian philosophers developed some of the earliest philosophical concepts of the universe.<ref name=Routledge /><ref>{{cite book|title=The Unfinished Universe|page=21|publisher=Oxford University Press|first=Louise B.|last=Young |year=1993 |isbn=978-0-195-08039-1 |oclc=26399171}}</ref> The earliest Greek philosophers noted that appearances can be deceiving, and sought to understand the underlying reality behind the appearances. In particular, they noted the ability of matter to change forms (e.g., ice to water to steam) and several philosophers proposed that all the physical materials in the world are different forms of a single primordial material, or ''[[arche]]''. The first to do so was [[Thales]], who proposed this material to be [[Water (classical element)|water]]. Thales' student, [[Anaximander]], proposed that everything came from the limitless ''[[Apeiron (cosmology)|apeiron]]''. [[Anaximenes of Miletus|Anaximenes]] proposed the primordial material to be [[Air (classical element)|air]] on account of its perceived attractive and repulsive qualities that cause the ''arche'' to condense or dissociate into different forms. [[Anaxagoras]] proposed the principle of ''[[Nous]]'' (Mind), while [[Heraclitus]] proposed [[fire (classical element)|fire]] (and spoke of ''[[logos]]''). [[Empedocles]] proposed the elements to be earth, water, air and fire. His four-element model became very popular. Like [[Pythagoras]], [[Plato]] believed that all things were composed of [[number]], with Empedocles' elements taking the form of the [[Platonic solids]]. [[Democritus]], and later philosophers—most notably [[Leucippus]]—proposed that the universe is composed of indivisible [[atom]]s moving through a [[void (astronomy)|void]] ([[vacuum]]), although [[Aristotle]] did not believe that to be feasible because air, like water, offers [[Drag (physics)|resistance to motion]]. Air will immediately rush in to fill a void, and moreover, without resistance, it would do so indefinitely fast.<ref name=Routledge />

Although Heraclitus argued for eternal change,<ref>{{cite SEP|url-id=heraclitus |title=Heraclitus |date=September 3, 2019 |last=Graham |first=Daniel W.}}</ref> his contemporary [[Parmenides]] emphasized changelessness. Parmenides' poem ''On Nature'' has been read as saying that all change is an illusion, that the true underlying reality is eternally unchanging and of a single nature, or at least that the essential feature of each thing that exists must exist eternally, without origin, change, or end.<ref>{{cite SEP|url-id=parmenides |title=Parmenides |date=October 19, 2020 |first=John |last=Palmer}}</ref> His student [[Zeno of Elea]] challenged everyday ideas about motion with several famous [[Zeno's paradoxes|paradoxes]]. Aristotle responded to these paradoxes by developing the notion of a potential countable infinity, as well as the infinitely divisible continuum.<ref>{{cite SEP|url-id=zeno-elea |title=Zeno of Elea |date=April 8, 2021 |first=John |last=Palmer}}</ref><ref>{{cite IEP|url-id=zenos-paradoxes |title=Zeno's Paradoxes |first=Bradley |last=Dowden}}</ref> Unlike the eternal and unchanging cycles of time, he believed that the world is bounded by the celestial spheres and that cumulative stellar magnitude is only finitely multiplicative.

The [[Indian philosophy|Indian philosopher]] [[Kanada (philosopher)|Kanada]], founder of the [[Vaisheshika]] school, developed a notion of [[atomism]] and proposed that [[light]] and [[heat]] were varieties of the same substance.<ref>[[Will Durant]], ''Our Oriental Heritage'': {{blockquote|"Two systems of Hindu thought propound physical theories suggestively similar to those of [[Ancient Greece|Greece]]. Kanada, founder of the Vaisheshika philosophy, held that the world is composed of atoms as many in kind as the various elements. The [[Jainism|Jains]] more nearly approximated to [[Democritus]] by teaching that all atoms were of the same kind, producing different effects by diverse modes of combinations. Kanada believed light and heat to be varieties of the same substance; [[Udayana]] taught that all heat comes from the Sun; and [[Vācaspati Miśra|Vachaspati]], like [[Isaac Newton|Newton]], interpreted light as composed of minute particles emitted by substances and striking the eye."}}</ref> In the 5th century AD, the [[Buddhist atomism|Buddhist atomist]] philosopher [[Dignāga]] proposed [[atom]]s to be point-sized, durationless, and made of energy. They denied the existence of substantial matter and proposed that movement consisted of momentary flashes of a stream of energy.<ref>Stcherbatsky, F. Th. (1930, 1962), ''Buddhist Logic'', Volume 1, p. 19, Dover, New York: {{blockquote|"The Buddhists denied the existence of substantial matter altogether. Movement consists for them of moments, it is a staccato movement, momentary flashes of a stream of energy... "Everything is evanescent",... says the Buddhist, because there is no stuff... Both systems <nowiki>[</nowiki>[[Samkhya|Sānkhya]], and later Indian Buddhism<nowiki>]</nowiki> share in common a tendency to push the analysis of existence up to its minutest, last elements which are imagined as absolute qualities, or things possessing only one unique quality. They are called "qualities" (''guna-dharma'') in both systems in the sense of absolute qualities, a kind of atomic, or intra-atomic, energies of which the empirical things are composed. Both systems, therefore, agree in denying the objective reality of the categories of Substance and Quality,... and of the relation of Inference uniting them. There is in Sānkhya philosophy no separate existence of qualities. What we call quality is but a particular manifestation of a subtle entity. To every new unit of quality corresponds a subtle quantum of matter which is called ''guna'', "quality", but represents a subtle substantive entity. The same applies to early Buddhism where all qualities are substantive... or, more precisely, dynamic entities, although they are also called ''dharmas'' ('qualities')."}}</ref>

The notion of [[temporal finitism]] was inspired by the doctrine of creation shared by the three [[Abrahamic religions]]: [[Judaism]], [[Christianity]] and [[Islam]]. The [[Christian philosophy|Christian philosopher]], [[John Philoponus]], presented the philosophical arguments against the ancient Greek notion of an infinite past and future. Philoponus' arguments against an infinite past were used by the [[Early Islamic philosophy|early Muslim philosopher]], [[Al-Kindi]] (Alkindus); the [[Jewish philosophy|Jewish philosopher]], [[Saadia Gaon]] (Saadia ben Joseph); and the [[Kalam|Muslim theologian]], [[Al-Ghazali]] (Algazel).<ref name="Viney1985">{{cite book |author=Viney |first=Donald Wayne |title=Charles Hartshorne and the Existence of God |publisher=SUNY Press |year=1985 |isbn=978-0-87395-907-0 |pages=65–68 |chapter=The Cosmological Argument}}</ref>

[[Pantheism]] is the [[Philosophy|philosophical]] [[Religion|religious]] belief that the universe itself is identical to [[divinity]] and a [[Deity|supreme being]] or entity.<ref name="Pearsall">{{cite book |last1=Pearsall |first1=Judy |title=The New Oxford Dictionary Of English |date=1998 |publisher=Clarendon Press |isbn=978-0-19-861263-6 |edition=1st |location=Oxford |page=1341}}</ref> The physical universe is thus understood as an all-encompassing, [[Immanence|immanent]] deity.<ref name="Edwards">{{cite book |last1=Edwards |first1=Paul |url=https://archive.org/details/encyclopediaofph08edwa |title=Encyclopedia of Philosophy |date=1967 |publisher=Macmillan |location=New York |page=[https://archive.org/details/encyclopediaofph08edwa/page/34 34] |url-access=registration}}</ref> The term 'pantheist' designates one who holds both that everything constitutes a unity and that this unity is divine, consisting of an all-encompassing, manifested [[God (male deity)|god]] or [[goddess]].<ref name="Edwards2">{{Cite book |title=Encyclopedia of Philosophy ed. Paul Edwards |publisher=Macmillan and Free Press |year=1967 |location=New York |page=34}}</ref><ref>{{cite book |last=Reid-Bowen |first=Paul |title=Goddess as Nature: Towards a Philosophical Thealogy |date=April 15, 2016 |publisher=[[Taylor & Francis]] |isbn=9781317126348 |page=70}}</ref> Pantheistic concepts date back thousands of years, and pantheistic elements have been identified in various religious traditions.

=== Astronomical concepts ===
{{Main|History of astronomy|Timeline of astronomy}}
[[File:Aristarchus working.jpg|thumb|right|3rd century BCE calculations by [[Aristarchus of Samos|Aristarchus]] on the relative sizes of, from left to right, the Sun, Earth, and Moon, from a 10th-century AD Greek copy]]

The earliest written records of identifiable [[history of astronomy|predecessors to modern astronomy]] come from [[Ancient Egypt]] and [[Mesopotamia]] from around 3000 to 1200 [[Common Era|BCE]].<ref name=Lindberg2007a>{{Cite book |last=Lindberg |first=David C. |title=The beginnings of Western science: the European Scientific tradition in philosophical, religious, and institutional context |publisher=University of Chicago Press |year=2007 |isbn=9780226482057 |edition=2nd |page=12}}</ref><ref name="Grant2007a">{{cite book |last=Grant |first=Edward |title=A History of Natural Philosophy: From the Ancient World to the Nineteenth Century |publisher=Cambridge University Press |year=2007 |isbn=978-0-521-68957-1 |edition=|location=New York |pages=1–26 |chapter=Ancient Egypt to Plato |chapter-url=https://archive.org/details/historynaturalph00gran/page/n16 |chapter-url-access=limited}}</ref> [[Babylonian astronomy|Babylonian astronomers]] of the 7th century BCE viewed the world as a [[Flat Earth|flat disk]] surrounded by the ocean,<ref>{{cite journal|first=Wayne |last=Horowitz |journal=Iraq |year=1988 |title=The Babylonian Map of the World |volume=50 |pages=147–165 |doi=10.2307/4200289 |jstor=4200289|s2cid=190703581 }}</ref><ref>{{cite book |last1=Keel |first1=Othmar |title=The Symbolism of the Biblical World |year=1997 |publisher=Eisenbrauns |isbn=978-1-575-06014-9 |url=https://books.google.com/books?id=Fy4B1iMg33YC |pages=20–22 |access-date=February 26, 2023 |archive-date=March 13, 2024 |archive-url=https://web.archive.org/web/20240313184352/https://books.google.com/books?id=Fy4B1iMg33YC |url-status=live }}</ref> and this forms the premise for early Greek maps like those of [[Anaximander]] and [[Hecataeus of Miletus]].

Later [[Ancient Greece|Greek]] philosophers, observing the motions of the heavenly bodies, were concerned with developing models of the universe based more profoundly on [[empirical evidence]]. The first coherent model was proposed by [[Eudoxus of Cnidos]], a student of Plato who followed Plato's idea that heavenly motions had to be circular. In order to account for the known complications of the planets' motions, particularly [[Retrograde and prograde motion|retrograde movement]], Eudoxus' model included 27 different [[celestial spheres]]: four for each of the planets visible to the naked eye, three each for the Sun and the Moon, and one for the stars. All of these spheres were centered on the Earth, which remained motionless while they rotated eternally. Aristotle elaborated upon this model, increasing the number of spheres to 55 in order to account for further details of planetary motion. For Aristotle, normal [[classical elements|matter]] was entirely contained within the terrestrial sphere, and it obeyed fundamentally different rules from [[Aether (classical element)|heavenly material]].<ref>{{Cite journal |last=Wright |first=Larry |date=August 1973 |title=The astronomy of Eudoxus: Geometry or physics? |url=https://linkinghub.elsevier.com/retrieve/pii/0039368173900022 |journal=Studies in History and Philosophy of Science |language=en |volume=4 |issue=2 |pages=165–172 |doi=10.1016/0039-3681(73)90002-2 |bibcode=1973SHPSA...4..165W |access-date=February 27, 2023 |archive-date=March 15, 2023 |archive-url=https://web.archive.org/web/20230315164807/https://linkinghub.elsevier.com/retrieve/pii/0039368173900022 |url-status=live }}</ref><ref>{{Citation |last=Dicati |first=Renato |title=The Ancients' Astronomy |date=2013 |url=http://link.springer.com/10.1007/978-88-470-2829-6_2 |work=Stamping Through Astronomy |pages=19–55 |place=Milano |publisher=Springer Milan |language=en |doi=10.1007/978-88-470-2829-6_2 |isbn=978-88-470-2828-9 |access-date=February 27, 2023 |archive-date=March 13, 2024 |archive-url=https://web.archive.org/web/20240313184405/https://link.springer.com/chapter/10.1007/978-88-470-2829-6_2 |url-status=live }}</ref>

The post-Aristotle treatise ''[[De Mundo]]'' (of uncertain authorship and date) stated, "Five elements, situated in spheres in five regions, the less being in each case surrounded by the greater—namely, earth surrounded by water, water by air, air by fire, and fire by ether—make up the whole universe".<ref name=1908DeMundo>{{cite book |url=https://archive.org/details/demundoarisrich |title=De Mundo |year=1914 |author=Aristotle |author2=Forster, E. S. |author3=Dobson, J. F. |page=[https://archive.org/details/demundoarisrich/page/2 2] |location=Oxford |publisher=The Clarendon Press}}</ref>

This model was also refined by [[Callippus]] and after concentric spheres were abandoned, it was brought into nearly perfect agreement with astronomical observations by [[Ptolemy]].<ref name="almagest">{{cite journal |last=Goldstein |first=Bernard R. |date=1997 |title=Saving the phenomena: the background to Ptolemy's planetary theory |journal=Journal for the History of Astronomy |volume=28 |issue=1 |pages=1–12 |bibcode=1997JHA....28....1G |doi=10.1177/002182869702800101 |s2cid=118875902}}</ref> The success of such a model is largely due to the mathematical fact that any function (such as the position of a planet) can be decomposed into a set of circular functions (the [[Fourier series|Fourier modes]]). Other Greek scientists, such as the [[Pythagoreans|Pythagorean]] philosopher [[Philolaus]], postulated (according to [[Stobaeus]]' account) that at the center of the universe was a "central fire" around which the [[Earth]], [[Sun]], [[Moon]] and [[planet]]s revolved in uniform circular motion.<ref>Boyer, C. (1968) [https://archive.org/details/AHistoryOfMathematics ''A History of Mathematics'']. Wiley, p. 54.</ref>

The [[Greek astronomy|Greek astronomer]] [[Aristarchus of Samos]] was the first known individual to propose a [[Heliocentrism|heliocentric]] model of the universe. Though the original text has been lost, a reference in [[Archimedes]]' book ''[[The Sand Reckoner]]'' describes Aristarchus's heliocentric model. Archimedes wrote:

<blockquote>You, King Gelon, are aware the universe is the name given by most astronomers to the sphere the center of which is the center of the Earth, while its radius is equal to the straight line between the center of the Sun and the center of the Earth. This is the common account as you have heard from astronomers. But Aristarchus has brought out a book consisting of certain hypotheses, wherein it appears, as a consequence of the assumptions made, that the universe is many times greater than the universe just mentioned. His hypotheses are that the fixed stars and the Sun remain unmoved, that the Earth revolves about the Sun on the circumference of a circle, the Sun lying in the middle of the orbit, and that the sphere of fixed stars, situated about the same center as the Sun, is so great that the circle in which he supposes the Earth to revolve bears such a proportion to the distance of the fixed stars as the center of the sphere bears to its surface.<ref>{{Cite book |last=Heath |first=Thomas |url=https://books.google.com/books?id=rZmHAAAAQBAJ |title=Aristarchus of Samos, the Ancient Copernicus: A History of Greek Astronomy to Aristarchus, Together with Aristarchus's Treatise on the Sizes and Distances of the Sun and Moon |date=2013 |publisher=Cambridge University Press |isbn=978-1-108-06233-6 |pages=302 |language=en |author-link=Thomas Heath (classicist) |access-date=February 26, 2023 |archive-date=March 13, 2024 |archive-url=https://web.archive.org/web/20240313184546/https://books.google.com/books?id=rZmHAAAAQBAJ |url-status=live }}</ref></blockquote>

Aristarchus thus believed the stars to be very far away, and saw this as the reason why [[stellar parallax]] had not been observed, that is, the stars had not been observed to move relative each other as the Earth moved around the Sun. The stars are in fact much farther away than the distance that was generally assumed in ancient times, which is why stellar parallax is only detectable with precision instruments. The geocentric model, consistent with planetary parallax, was assumed to be the explanation for the unobservability of stellar parallax.<ref>{{Cite book |last=Kolkata |first=James J. |url=http://iopscience.iop.org/book/978-1-6817-4100-0 |title=Elementary Cosmology: From Aristotle's Universe to the Big Bang and Beyond |date=2015 |publisher=IOP Publishing |isbn=978-1-68174-100-0 |doi=10.1088/978-1-6817-4100-0ch4 |access-date=February 27, 2023 |archive-date=June 5, 2018 |archive-url=https://web.archive.org/web/20180605142714/http://iopscience.iop.org/book/978-1-6817-4100-0 |url-status=live }}</ref>

[[File:Flammarion.jpg|thumb|right|[[Flammarion engraving]], Paris 1888]]

The only other astronomer from antiquity known by name who supported Aristarchus's heliocentric model was [[Seleucus of Seleucia]], a [[Hellenistic astronomer]] who lived a century after Aristarchus.<ref>{{cite journal|author-link=Otto E. Neugebauer|author=Neugebauer, Otto E. |date=1945|title=The History of Ancient Astronomy Problems and Methods|journal=Journal of Near Eastern Studies|volume=4|issue=1|pages= 166–173|quote=the [[Chaldaea]]n Seleucus from Seleucia|jstor=595168|doi=10.1086/370729|s2cid=162347339 }}</ref><ref>{{cite journal |author=Sarton |first=George |author-link=George Sarton |date=1955 |title=Chaldaean Astronomy of the Last Three Centuries B. C. |journal=Journal of the American Oriental Society |volume=75 |issue=3 |pages=166–173 [169] |doi=10.2307/595168 |jstor=595168 |quote=the heliocentrical astronomy invented by Aristarchos of Samos and still defended a century later by Seleucos the [[Babylonia]]n}}</ref><ref>William P. D. Wightman (1951, 1953), ''The Growth of Scientific Ideas'', Yale University Press. p. 38, where Wightman calls him [[Seleucus of Seleucia|Seleukos]] the [[Chaldea]]n.</ref> According to Plutarch, Seleucus was the first to prove the heliocentric system through [[reasoning]], but it is not known what arguments he used. Seleucus' arguments for a heliocentric cosmology were probably related to the phenomenon of [[tide]]s.<ref>[[Lucio Russo]], ''Flussi e riflussi'', Feltrinelli, Milano, Italy, 2003, {{ISBN|88-07-10349-4}}.</ref> According to [[Strabo]] (1.1.9), Seleucus was the first to state that the tides are due to the attraction of the Moon, and that the height of the tides depends on the Moon's position relative to the Sun.<ref>{{harvtxt|Bartel|1987|loc=p. 527}}</ref> Alternatively, he may have proved heliocentricity by determining the constants of a [[Geometry|geometric]] model for it, and by developing methods to compute planetary positions using this model, similar to [[Nicolaus Copernicus]] in the 16th century.<ref>{{harvtxt|Bartel|1987|loc=pp. 527–529}}</ref> During the [[Middle Ages]], [[Heliocentrism|heliocentric]] models were also proposed by the [[Islamic astronomy|Persian astronomers]] [[Ja'far ibn Muhammad Abu Ma'shar al-Balkhi|Albumasar]]<ref>{{harvtxt|Bartel|1987 |loc=pp. 534–537}}</ref> and [[Al-Sijzi]].<ref name=Nasr>{{Cite book |last=Nasr |first=Seyyed H. |author-link=Hossein Nasr |orig-year=1964 |date=1993 |title=An Introduction to Islamic Cosmological Doctrines |edition=2nd |publisher=1st edition by [[Harvard University Press]], 2nd edition by [[State University of New York Press]] |isbn=978-0-7914-1515-3 |pages=[https://archive.org/details/introductiontois00nasr/page/135 135–136] |url=https://archive.org/details/introductiontois00nasr/page/135 }}</ref>

[[File:ThomasDiggesmap.JPG|thumb|left|[[Copernican heliocentrism|Model of the Copernican Universe]] by [[Thomas Digges]] in 1576, with the amendment that the stars are no longer confined to a sphere, but spread uniformly throughout the space surrounding the [[planet]]s]]

The Aristotelian model was accepted in the [[Western world]] for roughly two millennia, until Copernicus revived Aristarchus's perspective that the astronomical data could be explained more plausibly if the [[Earth]] rotated on its axis and if the [[Sun]] were placed at the center of the universe.<ref name="TMU">{{Cite book |last1=Frautschi |first1=Steven C. |title=The Mechanical Universe: Mechanics and Heat |title-link=The Mechanical Universe |last2=Olenick |first2=Richard P. |last3=Apostol |first3=Tom M. |last4=Goodstein |first4=David L. |date=2007 |publisher=Cambridge University Press |isbn=978-0-521-71590-4 |edition=Advanced |location=Cambridge [Cambridgeshire] |page=58 |oclc=227002144 |author-link=Steven Frautschi |author-link3=Tom M. Apostol |author-link4=David L. Goodstein}}</ref>

{{blockquote|In the center rests the Sun. For who would place this lamp of a very beautiful temple in another or better place than this wherefrom it can illuminate everything at the same time?|Nicolaus Copernicus|in Chapter 10, Book 1 of ''De Revolutionibus Orbium Coelestrum'' (1543)}}

As noted by Copernicus, the notion that the [[Earth's rotation|Earth rotates]] is very old, dating at least to [[Philolaus]] ({{Circa|450 BC}}), [[Heraclides Ponticus]] ({{Circa|350 BC}}) and [[Ecphantus the Pythagorean]]. Roughly a century before Copernicus, the Christian scholar [[Nicholas of Cusa]] also proposed that the Earth rotates on its axis in his book, ''On Learned Ignorance'' (1440).<ref>[[#Misner|Misner, Thorne and Wheeler]], p. 754.</ref> Al-Sijzi<ref>{{cite book|title=Science in the Quran|volume=1|publisher=Malik Library|first=Ema Ākabara|last=Ālī|page=218}}</ref> also proposed that the Earth rotates on its axis. [[Empirical research|Empirical evidence]] for the Earth's rotation on its axis, using the phenomenon of [[comet]]s, was given by [[Nasīr al-Dīn al-Tūsī|Tusi]] (1201–1274) and [[Ali Qushji]] (1403–1474).<ref>{{Citation |last=Ragep |first=F. Jamil |year=2001 |title=Tusi and Copernicus: The Earth's Motion in Context |journal=Science in Context |volume=14 |issue=1–2 |pages=145–163 |doi=10.1017/s0269889701000060 |s2cid=145372613 }}</ref>

This cosmology was accepted by [[Isaac Newton]], [[Christiaan Huygens]] and later scientists.<ref name="Misner-p755">[[#Misner|Misner, Thorne and Wheeler]], pp. 755–756.</ref> Newton demonstrated that the same [[Newton's laws of motion|laws of motion]] and gravity apply to earthly and to celestial matter, making Aristotle's division between the two obsolete. [[Edmund Halley]] (1720)<ref name=m756>[[#Misner|Misner, Thorne and Wheeler]], p. 756.</ref> and [[Jean-Philippe de Chéseaux]] (1744)<ref>{{cite book |author=de Cheseaux JPL |title=Traité de la Comète |date=1744 |publisher=Lausanne |pages=223ff |author-link=Jean-Philippe de Cheseaux}}. Reprinted as Appendix II in {{cite book |author=Dickson |first=F. P. |title=The Bowl of Night: The Physical Universe and Scientific Thought |date=1969 |publisher=M.I.T. Press |isbn=978-0-262-54003-2 |location=Cambridge, Massachusetts |language=en-us}}</ref> noted independently that the assumption of an infinite space filled uniformly with stars would lead to the prediction that the nighttime sky would be as bright as the Sun itself; this became known as [[Olbers' paradox]] in the 19th century.<ref>{{cite journal |author=Olbers HWM |author-link=Heinrich Wilhelm Matthäus Olbers |date=1826 |title=Unknown title |journal=Bode's Jahrbuch |volume=111}}. Reprinted as Appendix I in {{cite book |author=Dickson |first=F. P. |title=The Bowl of Night: The Physical Universe and Scientific Thought |date=1969 |publisher=M.I.T. Press |isbn=978-0-262-54003-2 |location=Cambridge, Massachusetts |language=en-us}}</ref> Newton believed that an infinite space uniformly filled with matter would cause infinite forces and instabilities causing the matter to be crushed inwards under its own gravity.<ref name="Misner-p755" /> This instability was clarified in 1902 by the [[Jeans instability]] criterion.<ref>{{cite journal|last1=Jeans |first1=J. H. |date=1902 |title=The Stability of a Spherical Nebula |journal=[[Philosophical Transactions of the Royal Society A]] |volume=199 |pages=1–53 |issue=312–320 |doi=10.1098/rsta.1902.0012 |bibcode=1902RSPTA.199....1J |jstor=90845 |doi-access= }}</ref> One solution to these paradoxes is the [[Carl Charlier|Charlier]] universe, in which the matter is arranged hierarchically (systems of orbiting bodies that are themselves orbiting in a larger system, ''ad infinitum'') in a [[fractal]] way such that the universe has a negligibly small overall density; such a cosmological model had also been proposed earlier in 1761 by [[Johann Heinrich Lambert]].<ref name=r196 /><ref>[[#Misner|Misner, Thorne and Wheeler]], p. 757.</ref>

During the 18th century, [[Immanuel Kant]] speculated that [[nebula]]e could be entire galaxies separate from the Milky Way,<ref name="m756" /> and in 1850, [[Alexander von Humboldt]] called these separate galaxies ''Weltinseln'', or "world islands", a term that later developed into "island universes".<ref>{{Cite journal |last=Jones |first=Kenneth Glyn |date=February 1971 |title=The Observational Basis for Kant's Cosmogony: A Critical Analysis |url=http://journals.sagepub.com/doi/10.1177/002182867100200104 |journal=Journal for the History of Astronomy |language=en |volume=2 |issue=1 |pages=29–34 |doi=10.1177/002182867100200104 |bibcode=1971JHA.....2...29J |s2cid=126269712 |issn=0021-8286 |access-date=February 27, 2023 |archive-date=February 27, 2023 |archive-url=https://web.archive.org/web/20230227183635/https://journals.sagepub.com/doi/10.1177/002182867100200104 |url-status=live }}</ref><ref>{{Cite journal |last=Smith |first=Robert W. |date=February 2008 |title=Beyond the Galaxy: The Development of Extragalactic Astronomy 1885–1965, Part 1 |url=http://journals.sagepub.com/doi/10.1177/002182860803900106 |journal=Journal for the History of Astronomy |language=en |volume=39 |issue=1 |pages=91–119 |doi=10.1177/002182860803900106 |bibcode=2008JHA....39...91S |s2cid=117430789 |issn=0021-8286 |access-date=February 27, 2023 |archive-date=February 27, 2023 |archive-url=https://web.archive.org/web/20230227183635/https://journals.sagepub.com/doi/10.1177/002182860803900106 |url-status=live }}</ref> In 1919, when the [[Hooker Telescope]] was completed, the prevailing view was that the universe consisted entirely of the Milky Way Galaxy. Using the Hooker Telescope, [[Edwin Hubble]] identified [[Cepheid variable]]s in several spiral nebulae and in 1922–1923 proved conclusively that [[Andromeda Galaxy|Andromeda Nebula]] and [[Triangulum Nebula|Triangulum]] among others, were entire galaxies outside our own, thus proving that the universe consists of a multitude of galaxies.<ref name="SharovNovikov1993">{{cite book|last1=Sharov|first1=Aleksandr Sergeevich|last2=Novikov|first2=Igor Dmitrievich|title=Edwin Hubble, the discoverer of the big bang universe|url=https://books.google.com/books?id=ttEwkEdPc70C&pg=PA34|access-date=December 31, 2011|date=1993|publisher=Cambridge University Press|isbn=978-0-521-41617-7|page=34|archive-date=June 23, 2013|archive-url=https://web.archive.org/web/20130623075250/http://books.google.com/books?id=ttEwkEdPc70C&pg=PA34|url-status=live}}</ref>

The modern era of [[physical cosmology]] began in 1917, when [[Albert Einstein]] first applied his [[general theory of relativity]] to model the structure and dynamics of the universe.<ref name="einstein_1917">{{cite journal |last=Einstein |first=Albert |author-link=Albert Einstein |date=1917 |title=Kosmologische Betrachtungen zur allgemeinen Relativitätstheorie |journal=Preussische Akademie der Wissenschaften, Sitzungsberichte |series=1917 |volume=(part 1) |pages=142–152}}</ref> The discoveries of this era, and the questions that remain unanswered, are outlined in the sections above.

{{wide image|Observable Universe Logarithmic Map (horizontal layout english annotations).png|2250px|Map of the observable universe with some of the notable astronomical objects known as of 2018. The scale of length increases exponentially toward the right. Celestial bodies are shown enlarged in size to be able to understand their shapes.}}
{{multiple image
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 | header            = Location of the Earth in the universe
 | image1            = The Earth seen from Apollo 17.jpg
 | width1            = 82
 | caption1          = [[Earth]]
 | image2            = Solar System true color.jpg
 | width2            = 146
 | caption2          = [[Solar&nbsp;System]]
 | image3            = RadcliffeWave1.png
 | width3            = 146
 | caption3          = [[Radcliffe Wave]]
 | image4            = Milky Way Arms ssc2008-10.svg
 | width4            = 93
 | caption4          = [[Orion Arm]]
 | image5            = Artist's impression of the Milky Way (updated - annotated).jpg
 | width5            = 83
 | caption5          = [[Milky&nbsp;Way]]
 | image6            = Local Group and nearest galaxies.jpg
 | width6            = 111
 | caption6          = [[Local Group|Local&nbsp;Group]]
 | image7            = Local supercluster-ly.jpg
 | width7            = 86
 | caption7          = [[Virgo Supercluster|Virgo SCl]]
 | image8            = Observable universe r2.jpg
 | width8            = 83
 | caption8          = [[Laniakea Supercluster|Laniakea SCl]]
 | image9            = Observable Universe with Measurements 01.png
 | width9            = 83
 | caption9          = [[Observable universe]]
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}}