Timeline of cosmology
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{{for|a timeline of the cosmos (or universe)|Timeline of the Big Bang}}
{{Cosmology|cTopic=History}}
This '''timeline of cosmological theories''' and discoveries is a [[Chronology|chronological]] catalog of the evolution of humankind's understanding of the [[cosmos]] over the last two-plus millennia. Modern [[Cosmology|cosmological]] conceptions follow the development of the [[science|scientific discipline]] of [[physical cosmology]].
==Pre-1900==
* '''[[15th century BC|15th]]-[[8th century BC|8th centuries BCE]]''' - The ''[[Vedas]]'' describe ancient [[Hindu cosmology]], in which the [[universe]] goes through repeated cycles of creation, destruction and rebirth, with each cycle lasting 4,320,000 years
* '''[[8th century BCE]]''' - [[Yajnavalkya]] proposes a [[spherical Earth]] and a [[Lunisolar calendar|lunisolar cycle]], and was attributed [[Heliocentrism|heliocentric]] ideas
* '''[[4th century BCE]]''' - [[Aristotle]] proposes an [[Earth]]-centred universe in which the Earth is stationary and the universe is finite in extent but infinite in time
* '''[[3rd century BCE]]''' - [[Aristarchus of Samos]] proposes a [[Sun]]-centered universe
* '''[[2nd century BCE]]''' - [[Seleucus of Seleucia]] elaborates on Aristarchus' heliocentric universe, using the phenomenon of [[tide]]s to explain heliocentrism
* '''[[2nd century]] CE''' - [[Ptolemy]] proposes an Earth-centred universe, with the Sun and planets revolving around the Earth
* '''[[5th century|5th]]-[[11th century|11th centuries]]''' - Several astronomers propose a Sun-centered universe, including [[Aryabhata]], [[Ja'far ibn Muhammad Abu Ma'shar al-Balkhi|Albumasar]] and [[Al-Sijzi]]
* '''[[6th century]]''' - [[John Philoponus]] proposes a universe that is finite in [[time]] and argues against the ancient Greek notion of an infinite universe
* '''[[9th century|9th]]-[[12th century|12th centuries]]''' - [[Al-Kindi]] (Alkindus), [[Saadia Gaon]] (Saadia ben Joseph) and the [[Al-Ghazali]] (Algazel) support a universe that has a finite past and develop two logical arguments against the notion of an infinite past, one of which is later adopted by [[Immanuel Kant]]
* '''[[964]]''' - [[Abd al-Rahman al-Sufi]] (Azophi), a [[Islamic astronomy|Persian astronomer]], makes the first recorded observations of the [[Andromeda Galaxy]] and the [[Large Magellanic Cloud]], the first galaxies other than the Milky Way to be observed from Earth, in his ''[[Book of Fixed Stars]]''
* '''[[13th century]]''' - [[Nasīr al-Dīn al-Tūsī]] provides the first [[Empirical research|empirical evidence]] for the [[Earth's rotation]] on its axis
* '''[[15th century]]''' - [[Ali Kuşçu]] provides empirical evidence for the Earth's rotation on its axis and rejects the stationary Earth theories of Aristotle and Ptolemy
* '''[[15th century|15th]]-[[16th century|16th centuries]]''' - [[Nilakantha Somayaji]] and [[Tycho Brahe]] propose a universe in which the planets orbit the Sun and the Sun orbits the Earth, known as the [[Tychonic system]]
* '''[[1543]]''' - [[Nicolaus Copernicus]] publishes his [[Copernican heliocentrism|heliocentric universe]] in his ''[[De revolutionibus orbium coelestium]]''
* '''[[1576]]''' - [[Thomas Digges]] modifies the [[Copernicus|Copernican]] system by removing its outer edge and replacing the edge with a [[star]]-filled unbounded space
* '''[[1584]]''' - [[Giordano Bruno]] proposes a non-hierarchical cosmology, wherein the Copernican [[solar system]] is not the centre of the universe, but rather, a relatively insignificant [[star system]], amongst an infinite multitude of others
* '''[[1610]]''' - [[Johannes Kepler]] uses the dark night sky to argue for a finite universe
* '''[[1687]]''' - Sir Isaac Newton's [[Physical law|laws]] describe large-scale motion throughout the universe
* '''[[1720]]''' - [[Edmund Halley]] puts forth an early form of [[Olbers' paradox]]
* '''[[1744]]''' - [[Jean-Philippe de Cheseaux]] puts forth an early form of Olbers' paradox
* '''[[1791]]''' - [[Erasmus Darwin]] pens the first description of a cyclical expanding and contracting universe in his poem ''[[The Botanic Garden|The Economy of Vegetation]]''
* '''[[1826]]''' - [[Heinrich Wilhelm Olbers]] puts forth [[Olbers' paradox]]
* '''[[1848]]''' - [[Edgar Allan Poe]] offers first correct solution to Olbers' paradox in ''[[Eureka: A Prose Poem]]'', an essay that also suggests the expansion and collapse of the universe
==1900-1949==
* '''[[1905]]''' - [[Albert Einstein]] publishes the [[Special Relativity|Special Theory of Relativity]], positing that space and time are not separate continua
* '''[[1915]]''' - Albert Einstein publishes the [[General Theory of Relativity]], showing that an energy density warps [[spacetime]]
* '''[[1917]]''' - [[Willem de Sitter]] derives an isotropic static cosmology with a [[cosmological constant]], as well as an empty [[metric expansion of space|expanding cosmology]] with a cosmological constant, termed a [[de Sitter universe]]
* '''[[1922]]''' - [[Vesto Slipher]] summarizes his findings on the [[galaxy|spiral nebulae]]'s systematic [[redshift]]s
* '''1922''' - [[Alexander Friedmann]] finds a solution to the [[Einstein field equation]]s which suggests a general expansion of space
* '''[[1927]]''' - [[Georges Lemaître]] discusses the creation event of an expanding universe governed by the Einstein field equations
* '''[[1928]]''' - [[Howard Percy Robertson]] briefly mentions that Vesto Slipher's redshift measurements combined with brightness measurements of the same galaxies indicate a redshift-distance relation
* '''[[1929]]''' - [[Edwin Hubble]] demonstrates the linear redshift-distance relation and thus shows the expansion of the universe
* '''[[1933]]''' - [[Edward Milne]] names and formalizes the [[cosmological principle]]
* '''[[1934]]''' - [[Georges Lemaître]] interprets the cosmological constant as due to a [[vacuum energy]] with an unusual perfect fluid [[equation of state]]
* '''[[1938]]''' - [[Paul Dirac]] suggests the [[Dirac large numbers hypothesis|large numbers hypothesis]], that the gravitational constant may be small because it is decreasing slowly with time
* '''[[1948]]''' - [[Ralph Alpher]], [[Hans Bethe]] ("in absentia"), and [[George Gamow]] examine element synthesis in a rapidly expanding and cooling universe, and suggest that the elements were produced by rapid [[neutron]] capture
* '''1948''' - [[Hermann Bondi]], [[Thomas Gold]], and [[Fred Hoyle]] propose [[steady state theory|steady state]] cosmologies based on the perfect cosmological principle
* '''1948''' - [[George Gamow]] predicts the existence of the [[cosmic microwave background radiation]] by considering the behavior of primordial radiation in an expanding universe
==1950 to 1999==
* '''1950''' - [[Fred Hoyle]] derisively [[Neologism|coins]] the term "Big Bang".
* '''[[1961]]''' - [[Robert Dicke]] argues that [[carbon]]-based [[life]] can only arise when the gravitational force is small, because this is when burning stars exist; first use of the weak [[anthropic principle]]
* '''[[1965]]''' - [[Hannes Alfvén]] proposes the now-discounted concept of [[ambiplasma]] to explain [[baryon asymmetry]].
* '''1965''' - [[Martin Rees]] and [[Dennis Sciama]] analyze [[quasar]] source count data and discover that the quasar density increases with redshift.
* '''1965''' - [[Arno Penzias]] and [[Robert Woodrow Wilson|Robert Wilson]], astronomers at [[Bell Labs]] discover the 2.7 K ''microwave background radiation'', which earns them the 1978 [[Nobel Prize]] in Physics. [[Robert Dicke]], [[Philip James Edwin Peebles|James Peebles]], Peter Roll and [[David Todd Wilkinson]] interpret it as relic from the big bang.
* '''[[1966]]''' - [[Stephen Hawking]] and [[George Ellis]] show that any plausible general relativistic cosmology is [[gravitational singularity|singular]]
* '''1966''' - [[James Peebles]] shows that the hot [[Big Bang]] predicts the correct helium abundance
* '''[[1967]]''' - [[Andrei Sakharov]] presents the requirements for [[baryogenesis]], a [[baryon]]-[[antimatter|antibaryon]] [[asymmetry]] in the universe
* '''1967''' - [[John Bahcall]], [[Wal Sargent]], and [[Maarten Schmidt]] measure the fine-structure splitting of [[spectral line]]s in 3C191 and thereby show that the [[fine-structure constant]] does not vary significantly with time
* '''[[1968]]''' - [[Brandon Carter]] speculates that perhaps the fundamental constants of nature must lie within a restricted range to allow the emergence of life; first use of the strong anthropic principle
* '''[[1969]]''' - [[Charles Misner]] formally presents the Big Bang horizon problem
* 1969 - [[Robert Dicke]] formally presents the Big Bang flatness problem
* '''[[1973]]''' - [[Edward Tryon]] proposes that the universe may be a large scale [[quantum mechanics|quantum mechanical]] [[vacuum fluctuation]] where positive mass-energy is balanced by negative gravitational [[potential energy]]
* '''[[1974]]''' - [[Robert Wagoner]], [[William Alfred Fowler|William Fowler]], and Fred Hoyle show that the hot Big Bang predicts the correct [[deuterium]] and [[lithium]] abundances
* '''[[1976]]''' - [[Alex Shlyakhter]] uses [[samarium]] ratios from the [[Oklo]] prehistoric [[natural nuclear fission reactor]] in [[Gabon]] to show that some laws of physics have remained unchanged for over two billion years
* '''[[1977]]''' - [[Gary Steigman]], [[David Schramm]], and [[James Gunn (astronomer)|James Gunn]] examine the relation between the primordial helium abundance and number of neutrinos and claim that at most five [[lepton]] families can exist.
* '''[[1981]]''' - [[Viacheslav Mukhanov]] and G. Chibisov propose that quantum fluctuations could lead to large scale structure in an [[cosmic inflation|inflationary]] universe
* '''[[1981]]''' - [[Alan Guth]] proposes the [[cosmic inflation|inflation]]ary Big Bang universe as a possible solution to the horizon and flatness problems
* '''[[1990]]''' - Preliminary results from [[NASA]]'s [[COBE]] mission confirm the [[cosmic microwave background radiation]] is an [[isotropic]] [[blackbody]] to an astonishing one part in 10<sup>5</sup> precision, thus eliminating the possibility of an integrated starlight model proposed for the background by steady state enthusiasts.
* '''[[1990s]]''' - Ground based cosmic microwave background experiments measure the first peak, determine that the universe is [[shape of the universe|geometrically flat]].
* '''[[1998]]''' - Controversial evidence for the [[fine structure constant]] varying over the lifetime of the universe is first published.
* '''1998''' - [[Adam Riess]], [[Saul Perlmutter]] and others discover the [[dark energy|cosmic acceleration]] in observations of [[Type Ia supernova]]e providing the first evidence for a non-zero [[cosmological constant]].
* '''1999''' - Measurements of the [[cosmic microwave background radiation]] (most notably by the [[BOOMERanG experiment]] see Mauskopf et al., 1999, Melchiorri et al., 1999, de Bernardis et al. 2000) provide evidence for oscillations (peaks) in the [[anisotropy]] angular spectrum as expected in the standard model of cosmological structure formation. These results indicates that the geometry of the universe is flat. Together with large scale structure data, this provides complementary evidence for a non-zero cosmological constant.
==Since 2000==
* '''[[2003]]''' - NASA's [[WMAP]] takes more detailed pictures of the cosmic microwave background radiation than were obtained by the [[BOOMERanG experiment]]. The image can be interpreted to indicate that the universe is 13.7 billion years old (within one percent error) and confirm that the [[Lambda-CDM model]] and the [[cosmic inflation|inflation]]ary theory are correct.
* '''[[2003]]''' - The [[Sloan Great Wall]] is discovered.
* '''[[2006]]''' - The long-awaited three-year [[WMAP]] results are released, confirming previous analysis, correcting several points, and including [[Cosmic microwave background radiation#Polarization|polarization]] data.
<!--- More informative details could be added here. --->
==See also==
*[[Timeline of the Big Bang]]
*[[List of cosmologists]]
* [[Non-standard cosmology]]
* [[Buddhist cosmology]]
* [[Hindu cosmology]]
* [[Maya mythology]]
==References==
* Bunch, Bryan, and Alexander Hellemans, "''The History of Science and Technology: A Browser's Guide to the Great Discoveries, Inventions, and the People Who Made Them from the Dawn of Time to Today''". ISBN 0-618-22123-9
* P. Mauskopf et al.,astro-ph/9911444, Astrophys.J. 536 (2000) L59-L62.
* A. Melchiorri et al.,astro-ph/9911445, Astrophys.J. 536 (2000) L63-L66.
* P. de Bernardis et al., astro-ph/0004404, Nature 404 (2000) 955-959.
{{DEFAULTSORT:Cosmology}}
[[Category:Astronomy timelines]]
[[Category:Physical cosmology]]
[[bn:বিশ্বতত্ত্বের কালপঞ্জি]]
[[ca:Cronologia de la cosmologia]]
[[es:Cronología de la cosmología]]
[[pt:Cronologia da cosmologia]]
[[fi:Kosmologian aikajana]]
[[sv:Kosmologins tidslinje]]