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| {{Cosmology}}
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| Observations suggest that the expansion of the [[universe]] will continue forever. If so, the universe will cool as it expands, eventually becoming too cold to sustain [[life]]. For this reason, this future scenario is popularly called the ''Big Freeze''.<ref>[http://map.gsfc.nasa.gov/universe/uni_fate.html WMAP – Fate of the Universe], ''WMAP's Universe'', [[NASA]]. Accessed on line July 17, 2008.</ref>
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| If [[dark energy]]—represented by the [[cosmological constant]], a ''constant'' energy density filling space homogeneously,<ref name="carroll">{{cite journal|author=[[Sean M. Carroll|Sean Carroll]]|year=2001|url=http://relativity.livingreviews.org/Articles/lrr-2001-1/index.html|title=The cosmological constant|journal=Living Reviews in Relativity|volume=4|accessdate=2006-09-28}}</ref> or [[Scalar field theory|scalar fields]], such as [[quintessence (physics)|quintessence]] or [[moduli (physics)|moduli]], ''dynamic'' quantities whose energy density can vary in time and space—accelerates the expansion of the universe, the space between clusters of [[galaxies]] will grow at an increasing rate. [[Redshift]] will stretch ancient, incoming photons (even gamma rays) to undetectably long wavelengths and low energies.<ref name=lun /> [[Star]]s are expected to form normally for 10<sup>12</sup> to 10<sup>14</sup> (1–100 trillion) years, but eventually the supply of gas needed for [[star formation]] will be exhausted. And as existing stars run out of fuel and cease to shine, the universe will slowly and inexorably grow darker, one star at a time.<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}} {{arxiv|astro-ph/9701131}}.</ref><sup> §IID, </sup><ref name=dying-IIE>Adams & Laughlin (1997), §IIE.</ref> According to theories that predict [[proton decay]], the [[compact star|stellar remnants]] left behind will disappear, leaving behind only [[black hole]]s, which themselves eventually disappear as they emit [[Hawking radiation]].<ref name=dying-IV>Adams & Laughlin (1997), §IV.</ref> Ultimately, if the universe reaches a state in which the temperature approaches a uniform value, no further [[work (thermodynamics)|work]] will be possible, resulting in a final [[heat death of the universe]].<ref name=dying-VID>Adams & Laughlin (1997), §VID</ref>
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| ==Cosmology==
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| Infinite expansion does not determine the spatial [[curvature]] of the universe. It can be open (with negative spatial curvature), flat, or closed (positive spatial curvature), although if it is closed, sufficient [[dark energy]] must be present to counteract the [[gravitational attraction]] of matter and other forces tending to contract the universe. Open and flat universes will expand forever even in the absence of dark energy.<ref name=calibrating>Chapter 7, ''Calibrating the Cosmos'', Frank Levin, New York: Springer, 2006, ISBN 0-387-30778-8.</ref>
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| Observations of the [[cosmic background radiation]] by the [[Wilkinson Microwave Anisotropy Probe]] suggest that the universe is spatially flat and has a significant amount of [[dark energy]].<ref name=wmap_5yr>[http://lambda.gsfc.nasa.gov/product/map/dr3/pub_papers/fiveyear/basic_results/wmap5basic.pdf Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Data Processing, Sky Maps, and Basic Results], G. Hinshaw et al., ''The Astrophysical Journal Supplement Series'' (2008), submitted, {{arxiv|0803.0732}}, {{bibcode|2008arXiv0803.0732H}}.</ref> In this case, the universe should continue to expand at an accelerating rate. The acceleration of the universe's expansion has also been confirmed by observations of distant [[supernovae]].<ref name=calibrating /> If, as in the [[Lambda-CDM model|concordance model]] of [[physical cosmology]] (Lambda-cold dark matter or ΛCDM), the dark energy is in the form of a [[cosmological constant]], the expansion will eventually become exponential, with the size of the universe doubling at a constant rate.
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| If the theory of [[inflation (cosmology)|inflation]] is true, the universe went through an episode dominated by a different form of dark energy in the first moments of the big bang; but inflation ended, indicating an equation of state much more complicated than those assumed so far for present-day dark energy. It is possible that the dark energy equation of state could change again resulting in an event that would have consequences which are extremely difficult to parametrize or predict.{{Citation needed|date=June 2011}}
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| ==Future history==
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| In the 1970s, the future of an expanding universe was studied by the astrophysicist [[Jamal Nazrul Islam|Jamal Islam]]<ref>Possible Ultimate Fate of the Universe, Jamal N. Islam, ''Quarterly Journal of the Royal Astronomical Society'' '''18''' (March 1977), pp. 3–8, {{bibcode|1977QJRAS..18....3I}}</ref> and the physicist [[Freeman Dyson]].<ref name=twoe>Time without end: Physics and biology in an open universe, Freeman J. Dyson, ''Reviews of Modern Physics'' '''51''' (1979), pp. 447–460, {{doi|10.1103/RevModPhys.51.447}}.</ref>
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| More recently, the astrophysicists [[Fred Adams]] and Gregory Laughlin have divided the past and future history of an expanding universe into five eras. The first, the ''Primordial Era'', is the time in the past just after the [[Big Bang]] when [[star]]s had not yet formed. The second, the ''Stelliferous Era'', includes the present day and all of the stars and [[galaxies]] we see. It is the time during which stars form from [[Molecular cloud|collapsing clouds of gas]]. In the subsequent ''Degenerate Era'', the stars will have burnt out, leaving all stellar-mass objects as [[compact star|stellar remnants]]—[[white dwarf]]s, [[neutron stars]], and [[black hole]]s. In the ''Black Hole Era'', white dwarfs, neutron stars, and other smaller [[astronomical objects]] have been destroyed by [[proton decay]], leaving only black holes. Finally, in the ''Dark Era'', even black holes have disappeared, leaving only a dilute gas of [[photons]] and [[leptons]].<ref name=fiveages /><sup>, pp. xxiv–xxviii.</sup>
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| This future history and the timeline below assume the continued expansion of the universe. If the universe begins to recontract, subsequent events in the timeline may not occur because the [[Big Crunch]], the recontraction of the universe
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| into a hot, dense state similar to that after the Big Bang, will supervene.<ref name=fiveages /><sup>, pp. 190–192;</sup><ref name=dying-VA>Adams & Laughlin (1997), §VA</ref>
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| ==Timeline==
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| :''For the past, including the Primordial Era, see [[Timeline of the Big Bang]].''
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| ===Stelliferous Era===
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| :''From 10<sup>6</sup> (1 million) years to 10<sup>14</sup> (100 trillion) years after the Big Bang''
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| {{See also|Graphical timeline of the Stelliferous Era}}
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| The observable universe is currently 1.38×10<sup>10</sup> (13.8 billion) years old.<ref name='planck_cosmological_parameters'>{{cite journal | arxiv=1303.5076 | title=Planck 2013 results. XVI. Cosmological parameters | author=Planck collaboration | journal=Submitted to Astronomy & Astrophysics | year=2013|bibcode = 2013arXiv1303.5076P }}</ref> This time is in the Stelliferous Era. About 155 million years after the Big Bang, the first star formed. Since then, stars have formed by the collapse of small, dense core regions in large, cold [[molecular cloud]]s of [[hydrogen]] gas. At first, this produces a [[protostar]], which is hot and bright because of energy generated by [[gravitational contraction]]. After the protostar contracts for a while, its center will become hot enough to [[nuclear fusion|fuse]] hydrogen and its lifetime as a star will properly begin.<ref name=fiveages /><sup>, pp. 35–39.</sup>
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| Stars whose mass is very low will eventually exhaust all their fusible [[hydrogen]] and then become [[helium]] [[white dwarf]]s.<ref name=endms>The End of the Main Sequence, Gregory Laughlin, Peter Bodenheimer, and Fred C. Adams, ''The Astrophysical Journal'', '''482''' (June 10, 1997), pp. 420–432. {{bibcode|1997ApJ...482..420L}}. {{doi|10.1086/304125}}.</ref> Stars of low to medium mass will expel some of their mass as a [[planetary nebula]] and eventually become [[white dwarfs]]; more massive stars will explode in a [[core-collapse supernova]], leaving behind [[neutron star]]s or [[stellar-mass black hole|black holes]].<ref name="evo">[http://adsabs.harvard.edu/abs/2003ApJ...591..288H How Massive Single Stars End Their Life], A. Heger, C. L. Fryer, S. E. Woosley, N. Langer, and D. H. Hartmann, ''Astrophysical Journal'' '''591''', #1 (2003), pp. 288–300.</ref> In any case, although some of the star's matter may be returned to the [[interstellar medium]], a [[compact star|degenerate remnant]] will be left behind whose mass is not returned to the interstellar medium. Therefore, the supply of gas available for [[star formation]] is steadily being exhausted.
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| ====Milky Way Galaxy and the Andromeda Galaxy merge into one====
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| :''3 billion years from now (17 billion years after the Big Bang)''
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| {{main|Andromeda–Milky Way collision}}
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| The [[Andromeda Galaxy]] is currently approximately 2.5 million light years away from our galaxy, the [[Milky Way Galaxy]], and they 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 will collide with one another and merge into one large galaxy based on current evidence. Up until 2012, there was no way to know whether the possible collision was definitely going to happen or not.<ref name=vanderMarel2012>{{cite journal|title=The M31 Velocity Vector. III. Future Milky Way M31-M33 Orbital Evolution, Merging, and Fate of the Sun | author=van der Marel, G. et al. | journal=The Astrophysical Journal | arxiv=1205.6865 | year=2012 | doi=10.1088/0004-637X/753/1/9 | volume=753 | bibcode=2012ApJ...753....9V|pages=9}}</ref> In 2012, researchers came to the conclusion that the collision is definite after using the Hubble Space Telescope between 2002 and 2010 to track the motion of Andromeda.<ref name="nature1">{{cite doi|10.1038/nature.2012.10765}}</ref>
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| ====Coalescence of Local Group====
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| :''10<sup>11</sup> (100 billion) to 10<sup>12</sup> (1 trillion) years''
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| 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>, §IIIA.</sup>
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| ====Galaxies outside the Local Supercluster are no longer detectable====
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| :''2×10<sup>12</sup> (2 trillion) years''
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| 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 longer be detectable in any way.<ref name=lun>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. 22–30. {{doi|10.1086/308434}}. {{bibcode|2000ApJ...531...22K}}.</ref>
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| === Degenerate Era===
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| :''From 10<sup>14</sup> (100 trillion) to 10<sup>40</sup> years''
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| By 10<sup>14</sup> (100 trillion) years from now, star formation will end, leaving all stellar objects in the form of [[compact star|degenerate remnants]]. This period, known as the Degenerate Era, will last until the degenerate remnants finally decay.<ref>Adams & Laughlin (1997), § III–IV.</ref>
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| ====Star formation ceases====
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| :''10<sup>14</sup> (100 trillion) years''
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| It is estimated that in 10<sup>14</sup> (100 trillion) years or less, star formation will end.<ref name=dying /><sup>, §IID.</sup> The least massive stars take the longest to exhaust their hydrogen fuel (see [[stellar evolution]]). Thus, the longest living stars in the universe are low-mass [[red dwarf]]s, with a mass of about 0.08 [[solar mass]]es, which have a lifetime of order 10<sup>13</sup> (10 trillion) years.<ref name=low_mass_lifetime>Adams & Laughlin (1997), §IIA and Figure 1.</ref> Coincidentally, this is comparable to the length of time over which star formation takes place.<ref name=dying /><sup> §IID.</sup> Once star formation ends and the least massive red dwarfs exhaust their fuel, [[nuclear fusion]] will cease. The low-mass red dwarfs will cool and become [[white dwarf]]s.<ref name=endms /> The only objects remaining with more than [[planemo|planetary mass]] will be [[brown dwarf]]s, with mass less than 0.08 solar masses, and [[compact star|degenerate remnants]]; [[white dwarf]]s, produced by stars with initial masses between about 0.08 and 8 solar masses; and [[neutron star]]s and [[stellar black hole|black hole]]s, produced by stars with initial masses over 8 solar masses. Most of the mass of this collection, approximately 90%, will be in the form of white dwarfs.<ref name=dying-IIE /> In the absence of any energy source, all of these formerly luminous bodies will cool and become faint.
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| The universe will become extremely dark after the last star burns out. Even so, there can still be occasional light in the universe. One of the ways the universe can be illuminated is if two [[carbon]]-[[oxygen]] white dwarfs with a combined mass of more than the [[Chandrasekhar limit]] of about 1.4 solar masses happen to merge. The resulting object will then undergo runaway thermonuclear fusion, producing a [[Type Ia supernova]] and dispelling the darkness of the [[Degenerate Era]] for a few weeks.<ref name=dying-IIIC>Adams & Laughlin (1997), §IIIC.</ref><ref>[http://spiff.rit.edu/classes/phys240/lectures/future/future.html The Future of the Universe], M. Richmond, lecture notes, "Physics 240", [[Rochester Institute of Technology]]. Accessed on line July 8, 2008.</ref> If the combined mass is not above the Chandrasekhar limit but is larger than the minimum mass to [[nuclear fusion|fuse]] carbon (about 0.9 solar masses), a [[carbon star]] could be produced, with a lifetime of around 10<sup>6</sup> (1 million) years.<ref name=fiveages /><sup>, p. 91</sup> Also, if two helium white dwarfs with a combined mass of at least 0.3 solar masses collide, a [[helium star]] may be produced, with a lifetime of a few hundred million years.<ref name=fiveages /><sup>, p. 91</sup> Finally, if brown dwarfs collide with each other, a [[red dwarf]] star may be produced which can survive for 10<sup>13</sup> (10 trillion) years.<ref name=dying-IIIC/><ref name=low_mass_lifetime />
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| ==== Planets fall or are flung from orbits by a close encounter with another star====
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| :''10<sup>15</sup> years''
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| Over time, the [[orbit]]s of planets will decay due to [[gravitational radiation]], or planets will be ejected from their local systems by [[gravitational perturbations]] caused by encounters with another [[compact star|stellar remnant]].<ref>Adams & Laughlin (1997), §IIIF, Table I.</ref>
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| ====Stellar remnants escape galaxies or fall into black holes====
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| :''10<sup>19</sup> to 10<sup>20</sup> years''
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| Over time, objects in a [[galaxy]] exchange [[kinetic energy]] in a process called [[dynamical relaxation]], making their velocity distribution approach the [[Maxwell-Boltzmann distribution]].<ref>p. 428, A deep focus on NGC 1883, A. L. Tadross, ''Bulletin of the Astronomical Society of India'' '''33''', #4 (December 2005), pp. 421–431, {{bibcode|2005BASI...33..421T}}.</ref> Dynamical relaxation can proceed either by close encounters of two stars or by less violent but more frequent distant encounters.<ref>[http://webusers.astro.umn.edu/~llrw/a4002/SG_notes.txt Reading notes], Liliya L. R. Williams, Astrophysics II: Galactic and Extragalactic Astronomy, [[University of Minnesota]], accessed on line July 20, 2008.</ref> In the case of a close encounter, two [[brown dwarfs]] or [[compact star|stellar remnants]] will pass close to each other. When this happens, the trajectories of the objects involved in the close encounter change slightly. After a large number of encounters, lighter objects tend to gain [[kinetic energy]] while the heavier objects lose it.<ref name=fiveages>''[[The Five Ages of the Universe]]'', Fred Adams and Greg Laughlin, New York: The Free Press, 1999, ISBN 0-684-85422-8.</ref><sup>, pp. 85–87</sup>
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| Because of dynamical relaxation, some objects will gain enough energy to reach galactic [[escape velocity]] and depart the galaxy, leaving behind a smaller, denser galaxy. Since encounters are more frequent in the denser galaxy, the process then accelerates. The end result is that most objects are ejected from the galaxy, leaving a small fraction (maybe 1% to 10%) which fall into the central [[supermassive black hole]].<ref name=dying /><sup>, §IIIAD;</sup><ref name=fiveages /><sup>, pp. 85–87</sup>
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| [[Image:BlackHole.jpg|thumb|right|245px|The [[supermassive black hole]]s are all that remains of galaxies once all protons decay, but even these giants are not immortal.]]
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| ==== Nucleons start to decay====
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| :''>10<sup>34</sup> years''
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| {{See also|Nucleon}}
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| The subsequent evolution of the universe depends on the existence and rate of [[proton decay]]. Experimental evidence shows that if the [[proton]] is unstable, it has a [[half-life]] of at least 10<sup>34</sup> years.<ref>G Senjanovic ''Proton decay and grand unification'', Dec 2009</ref> If any of the [[Grand Unified Theory|Grand Unified theories]] are correct, then there are theoretical reasons to believe that the half-life of the proton is under 10<sup>41</sup> years.<ref name=dying-IVA>Adams & Laughlin (1997), §IVA.</ref> [[Neutron]]s bound into [[atomic nucleus|nuclei]] are also expected to decay with a half-life comparable to the proton's.<ref name=dying-IVA/>
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| In the event that the proton does not decay at all, stellar-mass objects would still disappear, but more slowly. See [[#Future without proton decay|Future without proton decay]] below.
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| The rest of this timeline assumes that the proton half-life is approximately 10<sup>37</sup> years.<ref name=dying-IVA /> Shorter or longer proton half-lives will accelerate or decelerate the process. This means that after 10<sup>37</sup> years, one-half of all baryonic matter will have been converted into [[gamma ray]] [[photon]]s and [[leptons]] through proton decay.
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| ==== All nucleons decay====
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| :''10<sup>40</sup> years''
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| Given our assumed half-life of the proton, [[nucleons]] (protons and bound neutrons) will have undergone roughly 1,000 half-lives by the time the universe is 10<sup>40</sup> years old. To put this into perspective, there are an estimated 10<sup>80</sup> protons currently in the universe.<ref>[http://www.nap.edu/html/oneuniverse/frontiers_solution_17.html Solution, exercise 17], ''One Universe: At Home in the Cosmos'', Neil de Grasse Tyson, Charles Tsun-Chu Liu, and Robert Irion, Washington, D.C.: Joseph Henry Press, 2000. ISBN 0-309-06488-0.</ref> This means that the number of nucleons will be slashed in half 1,000 times by the time the universe is 10<sup>40</sup> years old. Hence, there will be roughly ½<sup>1,000</sup> (approximately 10<sup>−301</sup>) as many nucleons remaining as there are today; that is, ''zero'' nucleons remaining in the universe at the end of the Degenerate Age. Effectively, all baryonic matter will have been changed into [[photons]] and [[leptons]]. Some models predict the formation of stable [[positronium]] atoms with a greater diameter than the observable universe’s current diameter in 10<sup>85</sup> years, and that these will in turn decay to gamma radiation in 10<sup>141</sup> years.<ref name=dying /><sup> §IID, </sup><ref name=dying-IIE />
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| === Black Hole Era===
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| :''10<sup>40</sup> years to 10<sup>100</sup> years''
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| After 10<sup>40</sup> years, black holes will dominate the universe. They will slowly evaporate via [[Hawking radiation]].<ref name=dying /><sup>, §IVG.</sup> A black hole with a mass of around 1 solar mass will vanish in around 2×10<sup>66</sup> years. As the lifetime of a black hole is proportional to the cube of its mass, more massive black holes take longer to decay. A supermassive black hole with a mass of 10<sup>11</sup> (100 billion) solar masses will evaporate in around 2×10<sup>99</sup> years.<ref name=page>Particle emission rates from a black hole: Massless particles from an uncharged, nonrotating hole, Don N. Page, ''Physical Review D'' '''13''' (1976), pp. 198–206. {{doi|10.1103/PhysRevD.13.198}}. See in particular equation (27).</ref>
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| Hawking radiation has a [[thermal radiation|thermal spectrum]]. During most of a black hole's lifetime, the radiation has a low temperature and is mainly in the form of massless particles such as [[photon]]s and hypothetical [[graviton]]s. As the black hole's mass decreases, its temperature increases, becoming comparable to the [[Sun]]'s by the time the black hole mass has decreased to 10<sup>19</sup> kilograms. The hole then provides a temporary source of light during the general darkness of the Black Hole Era. During the last stages of its evaporation, a black hole will emit not only massless particles but also heavier particles such as [[electron]]s, [[positron]]s, [[proton]]s and [[antiproton]]s.<ref name=fiveages /><sup>, pp. 148–150.</sup> <span id="Dark Era" />
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| ====If protons do not decay as described above====
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| In the event the proton does not decay as described above, the Degenerate Era will last longer, and will overlap the Black Hole Era. In a timescale of approximately 10<sup>65</sup> years, apparently rigid objects such as [[Rock (geology)|rocks]] will be able to rearrange their atoms and molecules via [[quantum tunnelling]], behaving as a [[liquid]] does, but more slowly.<ref name=twoe /> However, the proton is still expected to decay, for example via processes involving [[virtual black hole]]s, or other higher-order processes, with a half-life of under 10<sup>200</sup> years.<ref name=dying /><sup>, §IVF</sup> For example, under the [[Standard Model]], groups of 2 or more nucleons are theoretically unstable because [[chiral anomaly]] allows processes that change baryon number by a multiple of 3.
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| ===Dark Era and Photon Age===
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| :''From 10<sup>100</sup> years''
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| [[Image:Photon waves.png|thumb|right|245px|The lonely [[photon]] is now king of the universe as the last of the [[supermassive black holes]] evaporates.]]
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| After all the black holes have evaporated (and after all the ordinary matter made of protons has disintegrated, if protons are unstable), the universe will be nearly empty. Photons, neutrinos, electrons, and positrons will fly from place to place, hardly ever encountering each other. Gravitationally, the universe will be dominated by [[dark matter]], electrons, and positrons (not protons).<ref name=dying-VD>Adams & Laughlin (1997), §VD.</ref>
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| By this era, with only very diffuse matter remaining, activity in the universe will have tailed off dramatically (compared with previous eras), with very low energy levels and very large time scales. Electrons and positrons drifting through space will encounter one another and occasionally form [[positronium]] atoms. These structures are unstable, however, and their constituent particles must eventually annihilate.<ref name=dying-VF3>Adams & Laughlin (1997), §VF3.</ref> Other low-level annihilation events will also take place, albeit very slowly. The universe now reaches an extremely low-energy state.
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| ===Beyond===
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| What happens after this is speculative. It is possible that a [[Big Rip]] event may occur far off into the future. Also, the universe may enter a second [[inflation (cosmology)|inflationary]] epoch, or, assuming that the current [[vacuum]] state is a [[false vacuum]], the vacuum may decay into a lower-energy state.<ref name=dying-VE>Adams & Laughlin (1997), §VE.</ref>
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| Finally, the universe may settle into this state forever, achieving true [[heat death of the universe|heat death]].
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| Presumably, extreme low-energy states imply that localized quantum events become major macroscopic phenomena rather than negligible microscopic events because the smallest perturbations make the biggest difference in this era, so there is no telling what may happen to space or time. It is perceived that the laws of "macro-physics" will break down, and the laws of "quantum-physics" will prevail.<ref name=dying-VID/>
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| The universe could possibly avoid eternal heat death, by spontaneous [[entropy]] decrease either through [[quantum tunnelling]] or a [[Poincaré recurrence theorem|Poincaré recurrence]]. Quantum tunnelling could produce a new Big Bang in roughly <math>10^{10^{56}}</math> years.<ref>Carroll, Sean M. and Chen, Jennifer (2004). {{cite article | title = Spontaneous Inflation and Origin of the Arrow of Time | arxiv = hep-th/0410270}}</ref> A Poincaré recurrence could generate a new Big Bang the size of the currently observable universe in <math>10^{10^{10^{10^{2.08}}}}</math> years. Finally, a Poincaré recurrence could occur for the entire Universe, observable or not, assuming Linde's chaotic inflationary model with an inflaton whose mass is 10<sup>−6</sup> Planck masses, in <math>10^{10^{10^{10^{10^{1.1}}}}}</math> years.<ref name="page95">{{cite book | chapter = Information Loss in Black Holes and/or Conscious Beings? | last = Page | first = Don N. | title = Heat Kernel Techniques and Quantum Gravity | year = 1995|editor=Fulling, S.A. | page = 461 | series = Discourses in Mathematics and its Applications | issue = 4 | publisher = Texas A&M University | arxiv = hep-th/9411193 | isbn = 978-0-9630728-3-2
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| }}</ref>
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| ==Future without proton decay==
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| If the proton does not decay, stellar-mass objects will still become [[black holes]], but more slowly. The following timeline assumes that [[proton decay]] does not take place.
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| === Matter decays into iron===
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| :''10<sup>1500</sup> years from now''
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| In 10<sup>1500</sup> years, [[Muon-catalyzed fusion|cold fusion]] occurring via [[quantum tunnelling]] should make the light [[atomic nucleus|nuclei]] in ordinary matter fuse into [[iron-56]] nuclei (see [[isotopes of iron]].) [[Nuclear fission|Fission]] and [[alpha-particle]] emission should make heavy nuclei also decay to iron, leaving stellar-mass objects as cold spheres of iron, called [[iron star]]s.<ref name=twoe />
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| ===Collapse of iron star to black hole===
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| :''<math>10^{10^{26}}</math> to <math>10^{10^{76}}</math> years from now''
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| Quantum tunnelling should also turn large objects into [[black hole]]s. Depending on the assumptions made, the time this takes to happen can be calculated as from <math>10^{10^{26}}</math> years to <math>10^{10^{76}}</math> years. Quantum tunnelling may also make iron stars collapse into [[neutron star]]s in around <math>10^{10^{76}}</math> years.<ref name=twoe />
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| | |
| ==Graphical timeline==
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| {{main|Graphical timeline from Big Bang to Heat Death}}
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| {{See also|Graphical timeline of our universe|Graphical timeline of the Big Bang}}
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| <timeline>
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| #ImageSize = width:1100 height:370 # too wide
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| ImageSize = width:1000 height:370
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| PlotArea = left:40 right:235 bottom:50 top:50
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| | |
| Colors =
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| id:period1 value:rgb(1,1,0.7) # light yellow
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| id:period2 value:rgb(0.7,0.7,1) # light blue
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| id:events value:rgb(1,0.7,1) # light purple
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| id:era2 value:lightorange
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| id:era1 Value:yellowgreen
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| | |
| DateFormat = yyyy
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| Period = from:-51 till:1000
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| TimeAxis = format:yyyy orientation:horizontal
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| ScaleMajor = unit:year increment:100 start:0
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| ScaleMinor = unit:year increment:10 start:-50
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| | |
| AlignBars = justify
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| | |
| BarData =
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| bar:Era
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| bar:Events
| |
| | |
| TextData =
| |
| fontsize:M
| |
| pos:(0,260)
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| text:"Big"
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| text:"Bang"
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| # pos:(880,260)
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| pos:(780,260)
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| text:"Heat"
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| text:"Death"
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| # pos:(880,90)
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| pos:(780,90)
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| text:"[[Logarithmic scale|log]]"
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| text:"year"
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| | |
| PlotData=
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| textcolor:black fontsize:M
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| | |
| width:110
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| bar:Era mark:(line,white) align:left shift:(0,0)
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| from:-51 till:6 shift:(0,35) color:era1 text:"The Primordial Era"
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| from:6 till:14 shift:(0,15) color:era2 text:"The Stelliferous Era"
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| from:14 till:40 shift:(0,-5) color:era1 text:"The Degenerate Era"
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| from:40 till:100 shift:(0,-25) color:era2 text:"The Black Hole Era"
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| from:100 till:1000 shift:(0,-45) color:era1 text:"The Dark Era"
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| | |
| width:110
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| bar:Events
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| color:events align:left shift:(43,3) mark:(line,teal)
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| at:-8 shift:(0,35) text:"One second"
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| at:8 shift:(-2,15) text:"First star began to shine"
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| at:10 shift:(-2,-5) text:"13.8 billion years, the present day"
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| at:14 shift:(0,-25) text:"The last star has died"
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| at:100 shift:(0,-45) text:"The last supermassive black holes have evaporated."
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| </timeline>
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| | |
| == See also ==
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| * [[Big Rip]]
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| * [[Big Crunch]]
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| * [[Big Bounce]]
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| * [[Big Bang]]
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| * [[Chronology of the universe]]
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| * [[Cyclic model]]
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| * [[Dyson's eternal intelligence]]
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| * [[Entropy (arrow of time)]]
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| * [[Final anthropic principle]]
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| * [[Graphical timeline of the Stelliferous Era]]
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| *[[Graphical timeline of the Big Bang]]
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| * [[Graphical timeline from Big Bang to Heat Death]]. This timeline uses the double-logarithmic scale for comparison with the graphical timeline included in this article.
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| *[[Graphical timeline of our universe]]. This timeline uses the more intuitive linear time, for comparison with this article.
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| *[[Heat death of the universe]]
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| *[[Timeline of the Big Bang]]
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| *[[Timeline of the far future]]
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| * [[The Last Question]], a short story by Isaac Asimov which considers the inevitable oncome of heat death in the universe and how it may be reversed.
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| * [[Ultimate fate of the Universe]]
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| | |
| ==References==
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| {{reflist|2}}
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| [[Category:Eschatology]]
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| [[Category:Physical cosmology]]
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| [[Category:Astronomy timelines]]
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| [[Category:Articles which contain graphical timelines]]
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| [[Category:Future|Universe]]
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