Timeline of the Big Bang 183277 225817983 2008-07-15T15:26:03Z Ashill 444450 /* Structure formation */ move material from [[heat death of the universe]] {{Cosmology}} {{External_Timeline|Graphical timeline of the Big Bang|Graphical timeline of the Big Bang}} This '''timeline of the Big Bang''' describes the events according to the [[scientific theory]] of the [[Big Bang]], using the cosmological time parameter of [[comoving coordinates]]. Observations suggest that the universe as we know it began around 13.7 billion years ago. Since then, the evolution of the universe has passed through three phases. The very early universe, which is still poorly understood, was the split second in which the universe was so hot that [[subatomic particle|particles]] had energies higher than those currently accessible in [[particle accelerator]]s on Earth. Therefore, while the basic features of this epoch have been worked out in the big bang theory, the details are largely based on educated guesses. Following this period, in the early universe, the evolution of the universe proceeded according to known [[high energy physics]]. This is when the first [[protons]], [[electrons]] and [[neutrons]] formed, then [[nuclei]] and finally [[atoms]]. With the formation of neutral hydrogen, the [[cosmic microwave background]] was emitted. Then matter started to aggregate into the first [[star]]s and ultimately galaxies, [[quasar]]s, [[clusters of galaxies]] and [[supercluster]]s formed. There are several alternative theories about the [[ultimate fate of the universe]]. == The very early universe == All ideas concerning the very early universe ([[cosmogony]]) are necessarily speculative. As of today no accelerator experiments probe energies of sufficient magnitude to provide any insight into the period. All proposed scenarios differ radically, some examples being: the [[Hartle-Hawking initial state]], [[string landscape]], [[Cosmic inflation|brane inflation]], [[string gas cosmology]], and the [[ekpyrotic universe]]. Some of these are mutually compatible, while others are not. === Augustinian era === :''Before the Big Bang'' In 1952, [[George Gamow]], one of the founding fathers of Big Bang cosmology, proposed that the period before the Big Bang be called the [[Augustinian era]],<ref>{{cite book | title=The Creation of the Universe | url=http://books.google.com/books?id=5awirwgmvAoC&dq=George+Gamow+augustine&pg=PA28&ots=9PBnXqIFc0&sig=megc4jqMz7uEZlArXzUN36stzHc&prev=http://www.google.com/search%3Fhl%3Den%26q%3DGeorge%2BGamow%2Baugustine%26btnG%3DGoogle%2BSearch&sa=X&oi=print&ct=result&cd=1#PPA28,M1 | author=[[George Gamow|Gamow, George]] | year=1961 | ISBN=0486438686 | publisher=Courier Dover Publications}} p. 28 "Thus nothing can be said about the pre-squeeze era of the universe, the era which may be properly called, "St. Augustine's era," since it was St. Augustine of Hippo who first raised the question as to 'what God was doing before He made heaven and earth.'"</ref> after the philosopher [[Saint Augustine]], who believed time was solely a property of the God-created Universe, so that there was no time prior to the creation of the universe. The phrase "Augustinian Era" is meant to convey the idea that the known laws of physics break down in a [[gravitational singularity]] of infinite density at the time [[zero]] of the Big Bang, so that according to [[Albert Einstein]]'s [[general relativity|general theory of relativity]] there were no times prior to that point. However, physicists believe that general relativity becomes incompatible with [[quantum mechanics]] at the [[Planck scale]], so that the predictions of general relativity cannot be trusted before the [[Planck era]] when energies and temperatures reached the Planck scale, and that we need a theory of [[quantum gravity|quantum gravitation]] before we can say anything about times before the Planck era.<ref>{{cite web | title = The Planck Era | url = http://csep10.phys.utk.edu/astr162/lect/cosmology/planck.html}}</ref> === The Planck epoch === :''Up to 10<sup>-43</sup> seconds after the Big Bang'' {{main|Planck epoch}} If [[supersymmetry]] is correct, then during this time the four fundamental forces &mdash; [[electromagnetism]], [[weak nuclear force]], [[strong nuclear force]] and [[gravitation]] &mdash; all have the same strength, so they are possibly unified into one fundamental force. Little is known about this epoch, although different theories propose different scenarios. [[General relativity]] proposes a [[gravitational singularity]] before this time, but under these conditions the theory is expected to break down due to [[quantum mechanics|quantum effects]]. Physicists hope that proposed theories of [[quantum gravity|quantum gravitation]], such as [[string theory]] and [[loop quantum gravity]], will eventually lead to a better understanding of this epoch. === The grand unification epoch === :''Between 10<sup>-43</sup> seconds and 10<sup>-36</sup> seconds after the Big Bang'' <ref> Ryden B: "Introduction to Cosmology", pg. 196 Addison-Wesley 2003 </ref> {{main|Grand unification epoch}} As the universe [[metric expansion of space|expands]] and cools from the Planck epoch, [[gravitation]] begins to separate from the fundamental [[gauge theory|gauge interactions]]: electromagnetism and the strong and weak nuclear forces. Physics at this scale may be described by a grand unified theory in which the [[gauge group]] of the [[Standard Model]] is embedded in a much larger group, which is broken to produce the observed forces of nature. Eventually, the grand unification is broken as the strong nuclear force separates from the [[electroweak force]]. This occurs as soon as inflation does. According to some theories, this should produce [[magnetic monopoles]]. [[Grand Unification Theory|Unification]] of the [[Strong interaction|strong]] and [[electroweak force]]s, means that the only particle expected at this time is the [[Higgs boson]]{{Fact|date=June 2008}}. === The electroweak epoch === :''Between 10<sup>-36</sup> seconds and 10<sup>-12</sup> seconds after the Big Bang''<ref> Ryden B: "Introduction to Cosmology", pg. 196 Addison-Wesley 2003 </ref> {{main|Electroweak epoch}} The temperature of the universe is low enough (10<sup>28</sup>K) to separate the strong force from the electroweak force (the name for the unified forces of [[electromagnetism]] and the [[weak interaction]]). This phase transition triggers a period of exponential expansion known as [[cosmic inflation]]. After inflation ends, particle interactions are still energetic enough to create large numbers of exotic particles, including [[W and Z bosons]] and [[Higgs boson]]s. ==== The inflationary epoch ==== :''Between 10<sup>-36</sup> seconds and 10<sup>-32</sup> seconds after the Big Bang'' {{main|Inflationary epoch}} The temperature, and therefore the time, at which [[cosmic inflation]] occurs is not known for certain. During inflation, the universe is [[shape of the universe|flattened]] (its spatial curvature is critical) and the universe enters a [[wiktionary:Homogeneous|homogeneous]] and [[isotropic]] rapidly expanding phase in which the seeds of structure formation are laid down in the form of a primordial spectrum of nearly-[[scale invariance|scale-invariant]] fluctuations. Some energy from photons becomes [[virtual particle|virtual]] [[quark]]s and [[hyperon]]s, but these particles decay quickly. One scenario suggests that prior to cosmic inflation, the universe was cold and empty, and the immense heat and energy associated with the early stages of the big bang was created through the phase change associated with the end of inflation. ==== Reheating ==== During reheating, the exponential expansion that occurred during inflation ceases and the potential energy of the [[inflaton]] <!-- inflaton is not a typo --> field decays into a hot, relativistic [[quark-gluon plasma|plasma]] of particles. If grand unification is a feature of our universe, then cosmic inflation must occur during or after the grand unification [[symmetry breaking|symmetry is broken]], otherwise magnetic monopoles would be seen in the visible universe. At this point, the universe is dominated by radiation; quarks, [[electron]]s and [[neutrino]]s form. ==== Baryogenesis ==== {{main|Baryogenesis}} No known physics can explain the fact that there are so many more [[baryon]]s in the universe than [[antimatter|antibaryons]]. In order for this to be explained, the [[Sakharov conditions]] must be met at some time after inflation. There are hints that this is possible in known physics and from studying grand unified theories, but the full picture is not known. == The early universe == After cosmic inflation ends, the universe is filled with a [[quark-gluon plasma]]. From this point onwards the physics of the early universe is better understood, and less speculative. ====Supersymmetry breaking==== {{main|Supersymmetry breaking}} If [[supersymmetry]] is a property of our universe, then it must be broken at an energy as low as 1 [[TeV]], the electroweak symmetry scale. The masses of particles and their [[superpartner]]s would then no longer be equal, which could explain why no superpartners of known particles have ever been observed. === The quark epoch === :''Between 10<sup>-12</sup> seconds and 10<sup>-6</sup> seconds after the Big Bang'' {{main|Quark epoch}} In electroweak symmetry breaking, at the end of the electroweak epoch, all the fundamental particles are believed to acquire a mass via the [[Higgs mechanism]] in which the [[Higgs boson]] acquires a [[vacuum expectation value]]. The [[fundamental interactions]] of [[gravitation]], [[electromagnetism]], the [[strong interaction]] and the [[weak interaction]] have now taken their present forms, but the temperature of the universe is still too high to allow quarks to bind together to form hadrons. === The hadron epoch === :''Between 10<sup>-6</sup> seconds and 1 second after the Big Bang'' {{main|Hadron epoch}} The quark-gluon plasma which composes the universe cools until [[hadron]]s, including baryons such as [[proton]]s and [[neutron]]s, can form. At approximately 1 second after the Big Bang [[neutrino]]s decouple and begin travelling freely through space. This [[cosmic neutrino background]], while unlikely to ever be observed in detail, is analogous to the [[cosmic microwave background]] that was emitted much later. (See above regarding the quark-gluon plasma, under the String Theory epoch) === The lepton epoch === :''Between 1 second and 3 minutes after the Big Bang'' {{main|Lepton epoch}} The majority of hadrons and anti-hadrons annihilate each other at the end of the hadron epoch, leaving [[lepton]]s and anti-leptons dominating the mass of the universe. Approximately 3 seconds after the Big Bang the temperature of the universe falls to the point where new lepton/anti-lepton pairs are no longer created and most leptons and anti-leptons are eliminated in [[annihilation]] reactions, leaving a small residue of leptons. === The photon epoch === :''Between 3 minutes and 380,000 years after the Big Bang'' {{main|Photon epoch}} After most leptons and anti-leptons are annihilated at the end of the lepton epoch the energy of the universe is dominated by [[photon]]s. These photons are still interacting frequently with charged protons, electrons and (eventually) [[atomic nucleus|nuclei]], and continue to do so for the next 300,000 years. ==== Nucleosynthesis ==== :''Between 3 minutes and 20 minutes after the Big Bang''<ref>[http://www.astro.ucla.edu/~wright/BBNS.html Detailed timeline of Big Bang nucleosynthesis processes]</ref> {{main|Big Bang nucleosynthesis}} During the photon epoch the temperature of the universe falls to the point where atomic nuclei can begin to form. Protons (hydrogen ions) and neutrons begin to combine into atomic nuclei in the process of [[nuclear fusion]]. However, nucleosynthesis only lasts for about seventeen minutes, after which time the temperature and density of the universe has fallen to the point where nuclear fusion cannot continue. At this time, there is about three times more hydrogen than helium-4 (by mass) and only trace quantities of other nuclei. === Matter domination: 70,000 years === At this time, the densities of non-relativistic matter (atomic nuclei) and relativistic radiation (photons) are equal. The [[Jeans length]], which determines the smallest structures that can form (due to competition between gravitational attraction and pressure effects), begins to fall and perturbations, instead of being wiped out by [[radiation free-streaming]], can begin to grow in amplitude. === Recombination: 240,000-310,000 years === <!--Note: This section is direct linked to by [[Big bang]] and [[Recombination]] Update those links if changing the section title.--> {{seealso|Cosmic microwave background}} [[Image:WMAP 2008.png|thumb|right|245px|<center>[[WMAP]] data shows the microwave background radiation variations throughout the Universe from our perspective, though the actual variations are much smoother than the diagram suggests</center>]] Hydrogen and helium ''atoms'' begin to form and the density of the universe falls. This is thought to have occurred somewhere between 240,000 and 310,000 years after the Big Bang.<ref> Ryden B: "Introduction to Cosmology", pg. 158 Addison-Wesley 2003 </ref>. Hydrogen and helium are at the beginning ionized, i.e. no electrons are bounded to the nuclei which are therefore electrically charged (+1 and +2 respectively). As the universe cools down, the electrons get captured by the ions making them neutral. This process is relatively fast (actually faster for the helium than for the hydrogen) and is known as recombination<ref> Mukhanov, V: "Physical foundations of Cosmology", pg. 120, Cambridge 2005 </ref>. At the end of recombination, most of the atoms in the universe are neutral, therefore the photons can now travel freely: the universe has become transparent. The photons emitted right after the recombination, that can therefore travel undisturbed, are those that we see in the [[cosmic microwave background]] (CMB) radiation. Therefore the [[CMB]] is a picture of the universe at the end of this epoch. ===Dark ages=== {{seealso|21 centimeter radiation}} Before [[Decoupling#Physical cosmology|decoupling]] occurs most of the photons in the universe are interacting with electrons and protons in the photon-baryon fluid. The universe is opaque or "foggy" as a result. There is light but not light we could observe through telescopes. The baryonic matter in the universe consisted of ionized plasma, and it only became neutral when it gained free electrons during "recombination," thereby releasing the photons creating the CMB. When the photons were released (or decoupled) the universe became transparent. At this point the only radiation emitted is the 21 cm spin [[hydrogen line|line of neutral hydrogen]]. There is currently an observational effort underway to detect this faint radiation, as it is in principle an even more powerful tool than the cosmic microwave background for studying the early universe. ==Structure formation== {{seealso|Large-scale structure of the cosmos|Structure formation}} [[Image:Hubble ultra deep field.jpg|thumb|right|245px|<center>The [[Hubble Ultra Deep Field]]s often showcase galaxies from an ancient era that tell us what the early Stelliferous Age was like.</center>]] [[Image:Hubble - infant galaxy.jpg|thumb|right|245px|<center>Another Hubble image shows an infant galaxy forming nearby, which means this happened very recently on the cosmological timescale. This is evidence that the Universe is not quite finished with galaxy formation yet.</center>]] Structure formation in the big bang model proceeds hierarchically, with smaller structures forming before larger ones. The first structures to form are [[quasar]]s, which are thought to be bright, early [[active galaxies]], and [[population III stars]]. Before this epoch, the evolution of the universe could be understood through linear cosmological [[perturbation theory]]: that is, all structures could be understood as small deviations from a perfect homogeneous universe. This is computationally relatively easy to study. At this point non-linear structures begin to form, and the computational problem becomes much more difficult, involving, for example, [[N-body simulation]]s with billions of particles. ===Reionization=== {{seealso|Reionization|21 centimeter radiation}} The first quasars form from gravitational collapse. The intense radiation they emit reionizes the surrounding universe. From this point on, most of the universe is composed of [[Plasma (physics)|plasma]]. ===Formation of stars=== {{seealso|Star formation}} The first stars, most likely [[Population III]] stars, form and start the process of turning the light elements that were formed in the Big Bang (hydrogen, helium and lithium) into heavier elements. However, as of yet there have been no observed [[Population III]] stars which leaves their formation a mystery.<ref>[http://www.physorg.com/news6689.html ''Ferreting Out The First Stars''; physorg.com]</ref> ===Formation of galaxies=== {{seealso|Galaxy formation}} Large volumes of matter collapse to form a galaxy. [[Population II]] stars are formed early on in this process, with [[Population I]] stars formed later. Johannes Schedler's project has identified a quasar CFHQS 1641+3755 at 12.7 billion light-years away<ref>[http://antwrp.gsfc.nasa.gov/apod/ap070906.html APOD: 2007 September 6 - Time Tunnel<!-- Bot generated title -->]</ref>, when the Universe was just 7 percent of its present age. On July 11, 2007, using the 10 metre Keck II telescope on Mauna Kea, Richard Ellis of the California Institute of Technology at Pasadena and his team found six star forming galaxies about 13.2 billion light years away and therefore created when the universe was only 500 million years old <ref> "New Scientist" 14th July 2007</ref>. Only about 10 of these really early objects are currently known <ref>[http://mcdonaldobservatory.org/news/releases/2007/0608a.html HET Helps Astronomers Learn Secrets of One of Universe's Most Distant Objects<!-- Bot generated title -->]</ref> The [[Hubble Ultra Deep Field]] shows a number of small galaxies merging to form larger ones, at 13 billion light years, when the Universe was only 5% its current age<ref>[http://antwrp.gsfc.nasa.gov/apod/ap040309.html]</ref>. Based upon the emerging science of [[nucleocosmochronology]], the Galactic thin disk of the Milky Way is estimated to have been formed 8.3 ± 1.8 billion years ago<ref>Eduardo F. del Peloso a1a, Licio da Silva a1, Gustavo F. Porto de Mello and Lilia I. Arany-Prado (2005), "The age of the Galactic thin disk from Th/Eu nucleocosmochronology: extended sample" (Proceedings of the International Astronomical Union (2005), 1: 485-486 Cambridge University Press)</ref>. ===Formation of groups, clusters and superclusters=== {{seealso|Large-scale structure of the cosmos}} Gravitational attraction pulls galaxies towards each other to form groups, clusters and superclusters. ===Formation of our solar system: 8 billion years=== {{seealso|Solar system}} Finally, objects on the scale of our solar system form. Our sun is a late-generation star, incorporating the debris from many generations of earlier stars, and formed roughly 5 billion years ago, or roughly 8 to 9 billion years after the big bang. ===Today: 13.7 billion years=== The best current data estimate the [[age of the universe]] today as 13.7 billion years since the big bang. Since the expansion of the universe appears to be accelerating, [[superclusters]] are likely to be the largest structures that will ever form in the universe. The present accelerated expansion prevents any more inflationary structures entering the horizon and prevents new gravitationally bound structures from forming. ==Further evolution of galaxies and structure== ===The Milky Way Galaxy and the Andromeda Galaxy merge into one galaxy=== {{main|Andromeda-Milky Way collision}} The [[Andromeda Galaxy]] is currently approximately 2.5 million light years away from our galaxy, the [[Milky Way Galaxy]], and the galaxies are moving towards each other at approximately 120 kilometers per second. Approximately three billion years from now, or 17 billion years after the Big Bang, the Milky Way and the Andromeda Galaxy may collide with one another and merge into one large galaxy. Because it is not known precisely how fast the Andromeda Galaxy is moving transverse to us, it is not certain that the collision will happen.<ref>[http://www.galaxydynamics.org/papers/GreatMilkyWayAndromedaCollision.pdf The Great Milky Way-Andromeda Collision], John Dubinski, ''Sky and Telescope'', October 2006. {{bibcode|2006S&T...112d..30D}}.</ref> ===Coalescence of Local Group=== The [[galaxies]] in the [[Local Group]], the cluster of galaxies which includes the Milky Way and the Andromeda Galaxy, are gravitationally bound to each other. It is expected that between 10<sup>11</sup> (100 billion) and 10<sup>12</sup> (1 trillion) years from now, their orbits will decay and the entire Local Group will merge into one large galaxy.<ref name=dying /><sup>,&nbsp;§IIIA.</sup> ===Galaxies outside the Local Supercluster are no longer detectable=== Assuming that [[dark energy]] continues to make the Universe expand at an accelerating rate, 2×10<sup>12</sup> (2 trillion) years from now, all galaxies outside the [[Local Supercluster]] will be [[red-shift]]ed to such an extent that even [[gamma ray]]s they emit will have wavelengths longer than the size of the [[observable universe]] of the time. Therefore, these galaxies will no be longer detectable in any way.<ref>Life, the Universe, and Nothing: Life and Death in an Ever-expanding Universe, Lawrence M. Krauss and Glenn D. Starkman, ''Astrophysical Journal'', '''531''' ([[March 1]], [[2000]]), pp. 22&ndash;30. {{doi|10.1086/308434}}. {{bibcode|2000ApJ...531...22K}}.</ref> ==Ultimate fate of the universe== {{Main|Ultimate fate of the universe}} As with interpretations of what happened in the very early universe, advances in fundamental physics are required before it will be possible to know the ultimate fate of the universe with any certainty. Below are some of the main possibilities. ===Heat death: 10<sup>14</sup> years and beyond=== {{main|Heat death of the universe}} This scenario is generally considered to be the most likely, as it occurs if the universe continues expanding as it has been. Over a time scale on the order of 10<sup>14</sup> years or less, existing [[star]]s burn out, stars cease to be created, and the universe goes dark.<ref name=dying>A dying universe: the long-term fate and evolution of astrophysical objects, Fred C. Adams and Gregory Laughlin, ''Reviews of Modern Physics'' '''69''', #2 (April 1997), pp. 337–372. {{bibcode|1997RvMP...69..337A}}. {{doi|10.1103/RevModPhys.69.337}}.</ref><sup>,&nbsp;§IID.</sup> Over a much longer time scale in the eras following this, the galaxy evaporates as the [[stellar remnants]] comprising it escape into space, and black holes evaporate via [[Hawking radiation]].<ref name=dying /><sup>,&nbsp;§III,&nbsp;§IVG.</sup> In some [[grand unified theories]], [[proton decay]] will convert the remaining interstellar gas and stellar remnants into leptons (such as positrons and electrons) and photons. Some positrons and electrons will then recombine into photons.<ref name=dying /><sup>,&nbsp;§IV,&nbsp;§VF.</sup> In this case, the universe has reached a high-[[entropy]] state consisting of a bath of particles and low-energy radiation. It is not known however whether it eventually achieves [[thermodynamic equilibrium]].<ref name=dying /><sup>,&nbsp;§VIB,&nbsp;VID.</sup> ===Big crunch: 100+ billion years=== {{seealso|Big Crunch}} If the energy density of [[dark energy]] were negative or the universe were [[shape of the Universe|closed]], then it would be possible that the expansion of the universe would reverse and the universe would contract towards a hot, dense state. This would be analogous to a time-reversal of the [[big bang]]. This is often proposed as part of an [[oscillatory universe]] scenario, such as the [[cyclic model]]. Current observations suggest that this model of the universe is unlikely to be correct, and the expansion will continue. ===Big rip: 200+ billion years=== {{seealso|Big Rip}} This scenario is possible only if the energy density of [[dark energy]] actually increases without limit over time. Such dark energy is called [[phantom energy]] and is unlike any known kind of energy (except the energy of [[virtual particle]]s). In this case, the expansion rate of the universe will increase without limit. Gravitationally bound systems, such as clusters of galaxies, galaxies, and ultimately the solar system will be torn apart. Eventually the expansion will be so rapid as to overcome the electromagnetic forces holding molecules and atoms together. Finally even atomic nuclei will be torn apart and the universe as we know it will end in an unusual kind of [[gravitational singularity]]. In other words, the universe will expand so much that the electromagnetic force holding things together will fall to this expansion, making things fall apart. ===Vacuum metastability event=== {{seealso|False vacuum}} If our universe is in a very long-lived [[false vacuum]], it is possible that the universe will [[quantum tunneling|tunnel]] into a lower energy state. If this happens, all structures will be destroyed instantaneously, without any forewarning. ==References== <!-- ---------------------------------------------------------- See http://en.wikipedia.org/wiki/Wikipedia:Footnotes for a discussion of different citation methods and how to generate footnotes using the <ref>, </ref> and <reference /> tags ----------------------------------------------------------- --> {{reflist}} ==External links== * PBS Online (2000). [http://www.pbs.org/deepspace/timeline/ From the Big Bang to the End of the Universe - The Mysteries of Deep Space Timeline]. Retrieved March 24, 2005. * [[Eric Schulman|Schulman, Eric]] (1997). [http://members.bellatlantic.net/~vze3fs8i/hist/hist.html The History of the Universe in 200 Words or Less]. Retrieved March 24, 2005. * Space Telescope Science Institute Office of Public Outreach (2005). [http://hubblesite.org/ Home of the Hubble Space Telescope]. Retrieved March 24, 2005. * [http://www.fnal.gov/pub/presspass/vismedia/gallery/graphics.html Fermilab graphics] (see "Energy time line from the Big Bang to the present" and "History of the Universe Poster") * [http://exploringtime.org/?page=segments Exploring Time] from [[Planck time]] to the lifespan of the universe *[http://www.nytimes.com/2006/03/17/science/space/17cosmos.html Astronomers' first detailed hint of what was going on less than a trillionth of a second after time began] *[http://www.universeadventure.org/ The Universe Adventure] {{DEFAULTSORT:Big bang}} [[Category:Astronomy timelines]] [[Category:Physical cosmology]] [[ar:خط زمني للانفجار العظيم]] [[bn:মহা বিস্ফোরণের কালপঞ্জি]] [[cs:Vznik a vývoj vesmíru]] [[es:Cronología del Big Bang]] [[it:Cronologia del Big Bang]] [[hu:A világegyetem története]] [[ja:宇宙の年表]] [[pt:Cronologia do Universo]] [[ru:Хронология Большого взрыва]] [[sr:Космолошка доба]] [[sh:Kozmološka kronologija]] [[fi:Alkuräjähdyksen aikajana]] [[sv:Universums historia]] [[zh:宇宙时间表]]