View source for Heat death of the universe

{{Short description|Possible fate of the universe}}
{{About|the entropic exhaustion of the universe|other uses|Heat Death of the Universe (disambiguation)}}
{{For the| heat related illness or death| Hyperthermia}}
{{Redirect|Big Freeze}}

{{Multiple issues|
{{Original research|date=September 2020}}
{{Update|date=August 2021}}
{{Expand Chinese|date=August 2021|topic=sci}}
}}

{{Physical cosmology|expansion}}

The '''heat death of the universe''' (also known as the '''Big Chill''' or '''Big Freeze''')<ref>[http://map.gsfc.nasa.gov/universe/uni_fate.html WMAP – Fate of the Universe], ''WMAP's Universe'', [[NASA]]. Accessed online July 17, 2008.</ref><ref>{{Cite book |last=Dyer |first=Alan |title=Insiders: Space |date=2007-07-24 |publisher=[[Simon & Schuster]] Books for Young Readers |isbn=978-1-4169-3860-6 |pages=40–41 |language=en}}</ref> is a [[hypothesis]] on the [[ultimate fate of the universe]], which suggests the [[universe]] will evolve to a state of no [[thermodynamic free energy]], and will therefore be unable to sustain processes that increase [[entropy]]. Heat death does not imply any particular [[Thermodynamic temperature#Internal energy at absolute zero|absolute temperature]]; it only requires that temperature differences or other processes may no longer be exploited to perform [[work (thermodynamics)|work]]. In the language of [[physics]], this is when the universe reaches [[thermodynamic equilibrium]].

If the [[curvature#Space|curvature]] of the universe is [[Shape of the universe|hyperbolic or flat]], or if [[dark energy]] is a positive [[cosmological constant]], the universe will continue expanding forever, and a heat death is expected to occur,<ref name="DftS">
{{Cite book
| title            = Death from the Skies!
| last             = Plait
| first            = Philip
| publisher        = Viking Adult
| isbn             = 978-0-670-01997-7
| publication-date = 16 October 2008
| page            = 259
| author-link      = Phil Plait
| title-link       = Death from the Skies!
| year             = 2008
}}</ref> with the universe cooling to approach equilibrium at a very low temperature after a long time period.

The hypothesis of heat death stems from the ideas of [[William Thomson, 1st Baron Kelvin|Lord Kelvin]] who, in the 1850s, took the [[theory of heat]] as [[mechanical energy]] loss in nature (as embodied in the first two [[laws of thermodynamics]]) and [[Extrapolation|extrapolated]] it to larger processes on a universal scale. This also allowed Kelvin to formulate the [[heat death paradox]], which disproves an infinitely old universe.<ref name="On the Age of the Sun's Heat"/>

==Origins of the idea==
The idea of heat death stems from the [[second law of thermodynamics]], of which one version states that entropy tends to increase in an [[isolated system]]. From this, the hypothesis implies that if the universe lasts for a sufficient time, it will [[asymptotically]] approach a state where all [[energy]] is evenly distributed. In other words, according to this hypothesis, there is a tendency in nature towards the [[dissipation]] (energy transformation) of [[mechanical energy]] (motion) into [[thermal energy]]; hence, by extrapolation, there exists the view that, in time, the mechanical movement of the universe will run down as work is converted to heat because of the second law.

The conjecture that all bodies in the universe cool off, eventually becoming too cold to support life, seems to have been first put forward by the French astronomer [[Jean Sylvain Bailly]] in 1777 in his writings on the history of astronomy and in the ensuing correspondence with [[Voltaire]]. In Bailly's view, all planets have an [[Internal heating|internal heat]] and are now at some particular stage of cooling. [[Jupiter]], for instance, is still too hot for life to arise there for thousands of years, while the [[Moon]] is already too cold. The final state, in this view, is described as one of "equilibrium" in which all motion ceases.<ref>
{{Cite book 
 |title       = A History of Modern Planetary Physics: Nebulous Earth
 |last        = Brush
 |first       = Stephen G.
 |author-link = Stephen G. Brush
 |publisher   = Cambridge University Press
 |year        = 1996
 |isbn        = 978-0-521-44171-1
 |volume      = 1
 |page        = [https://archive.org/details/historyofmodernp0000brus/page/77 77]
 |url         = https://archive.org/details/historyofmodernp0000brus/page/77
}}</ref>

The idea of heat death as a consequence of the laws of thermodynamics, however, was first proposed in loose terms beginning in 1851 by Lord Kelvin (William Thomson), who theorized further on the mechanical energy loss views of [[Nicolas Léonard Sadi Carnot|Sadi Carnot]] (1824), [[James Joule]] (1843) and [[Rudolf Clausius]] (1850). Thomson's views were then elaborated over the next decade by [[Hermann von Helmholtz]] and [[William Rankine]].<ref name="Energy and Empire" />

===History===
The idea of the heat death of the universe derives from discussion of the application of the first two [[laws of thermodynamics]] to universal processes. Specifically, in 1851, [[Lord Kelvin]] outlined the view, as based on recent experiments on the dynamical [[theory of heat]]: "heat is not a substance, but a dynamical form of mechanical effect, we perceive that there must be an equivalence between mechanical work and heat, as between cause and effect."<ref>Thomson, Sir William. (1851). [https://zapatopi.net/kelvin/papers/on_the_dynamical_theory_of_heat.html "On the Dynamical Theory of Heat, with numerical results deduced from Mr Joule's equivalent of a Thermal Unit, and M. Regnault's Observations on Steam"] Excerpts. [§§1–14 & §§99–100], ''[[Transactions of the Royal Society of Edinburgh]]'', March 1851, and ''[[Philosophical Magazine|Philosophical Magazine IV]]'', 1852. This version from ''Mathematical and Physical Papers'', vol. i, art. XLVIII, pp. 174.</ref>
[[Image:Baron Kelvin 1906.jpg|175px|right|thumb|[[William Thomson, 1st Baron Kelvin|Lord Kelvin]] originated the idea of universal heat death in 1852.]]

In 1852, Thomson published ''On a Universal Tendency in Nature to the Dissipation of Mechanical Energy'', in which he outlined the rudiments of the second law of thermodynamics summarized by the view that mechanical motion and the energy used to create that motion will naturally tend to dissipate or run down.<ref>Thomson, Sir William (1852). [https://zapatopi.net/kelvin/papers/on_a_universal_tendency.html "On a Universal Tendency in Nature to the Dissipation of Mechanical Energy"] ''[[Proceedings of the Royal Society of Edinburgh]]'' for 19 April 1852, also ''[[Philosophical Magazine]]'', Oct. 1852. This version from ''Mathematical and Physical Papers'', vol. i, art. 59, pp. 511.</ref> The ideas in this paper, in relation to their application to the age of the [[Sun]] and the dynamics of the universal operation, attracted the likes of William Rankine and Hermann von Helmholtz. The three of them were said to have exchanged ideas on this subject.<ref name="Energy and Empire">
{{Cite book
|title        = Energy and Empire: A Biographical Study of Lord Kelvin
|last1        = Smith
|first1       = Crosbie
|last2        = Wise
|first2       = M. Norton
|publisher    = Cambridge University Press
|year         = 1989
|isbn         = 978-0-521-26173-9
|page        = 500
|author-link2 = M. Norton Wise
}}</ref> In 1862, Thomson published "On the age of the Sun's heat", an article in which he reiterated his fundamental beliefs in the indestructibility of energy (the [[first law of thermodynamics|first law]]) and the universal dissipation of energy (the second law), leading to diffusion of heat, cessation of useful motion ([[work (physics)|work]]), and exhaustion of [[potential energy]], "lost irrecoverably" through the material universe, while clarifying his view of the consequences for the universe as a whole. Thomson wrote:

{{blockquote|The result would inevitably be a state of universal rest and death, if the universe were finite and left to obey existing laws. But it is impossible to conceive a limit to the extent of matter in the universe; and therefore science points rather to an endless progress, through an endless space, of action involving the transformation of [[potential energy]] into [[Work (physics)|palpable motion]] and hence into [[heat]], than to a single finite mechanism, running down like a clock, and stopping for ever.<ref name="On the Age of the Sun's Heat">
{{Cite magazine
| last        = Thomson
| first       = Sir William
| date        = 5 March 1862
| title       = On the Age of the Sun's Heat
| url         = https://zapatopi.net/kelvin/papers/on_the_age_of_the_suns_heat.html
| magazine    = [[Macmillan's Magazine]]
| volume      = 5
| pages       = 388–93
}}</ref>}}
The clock's example shows how Kelvin was unsure whether the universe would eventually achieve [[thermodynamic equilibrium]]. Thompson later speculated that restoring the dissipated energy in "''[[vis viva]]''" and then usable work&nbsp;– and therefore revert the clock's direction, resulting in a "rejuvenating universe"&nbsp;– would require "a creative act or an act possessing similar power".<ref name="britannica.com">{{cite web|url=https://www.britannica.com/biography/William-Thomson-Baron-Kelvin |publisher=Encyclopædia Britannica |author=Harold I. Sharlin |date=13 December 2019 |access-date=24 January 2020 |title=William Thomson, Baron Kelvin}}</ref><ref>{{cite magazine |last1=Otis |first1=Laura |year=2002 |title=Literature and Science in the Nineteenth Century: An Anthology |url= https://oxfordworldsclassics.com/view/10.1093/owc/9780199554652.001.0001/isbn-9780199554652 |magazine=OUP Oxford |volume=1 |pages=60–67}}</ref> Starting from this publication, Kelvin also introduced the [[heat death paradox]] (Kelvin's paradox), which challenged the classical concept of an infinitely old universe, since the universe has not achieved its thermodynamic equilibrium, thus further work and [[entropy production]] are still possible. The existence of stars and temperature differences can be considered an empirical proof that the universe is not infinitely old.<ref name="Thompson2015">''[https://www.britannica.com/science/thermodynamics/Entropy-and-heat-death Laws of Thermodynamics]'' Thompson and Clausius, [[Oxford University Press]], 2015.</ref><ref name="On the Age of the Sun's Heat"/>

In the years to follow both Thomson's 1852 and the 1862 papers, [[Helmholtz]] and [[Rankine]] both credited Thomson with the idea, along with his paradox, but read further into his papers by publishing views stating that Thomson argued that the universe will end in a "heat death" (Helmholtz), which will be the "end of all physical phenomena" (Rankine).<ref name="Energy and Empire" /><ref>
{{Cite web
|url          = http://webplaza.pt.lu/fklaess/html/HISTORIA.HTML
|title        = Physics Chronology
|archive-url  = https://web.archive.org/web/20110522124507/http://webplaza.pt.lu/fklaess/html/HISTORIA.HTML
|archive-date = 22 May 2011
}}</ref>{{Unreliable source?|date=September 2018}}

==Current status==
{{See also|Entropy#Cosmology|Entropy (arrow of time)#Cosmology}}

Proposals about the final state of the universe depend on the assumptions made about its ultimate fate, and these assumptions have varied considerably over the late 20th century and early 21st century. In a hypothesized [[Shape of the universe|"open" or "flat" universe]] that continues expanding indefinitely, either a heat death or a [[Big Rip]] is expected to eventually occur.<ref name="DftS" /><ref>{{Cite web |last=Consolmagno |first=Guy |date=2008-05-08 |title=Heaven or Heat Death? |url=https://www.thinkingfaith.org/articles/20080508_1.htm |url-status=live |archive-url=https://web.archive.org/web/20231116170349/https://www.thinkingfaith.org/articles/20080508_1.htm |archive-date=2023-11-16 |access-date=2008-10-06 |website=Thinking Faith |language=en}}</ref> If the [[cosmological constant]] is zero, the universe will approach [[absolute zero]] temperature over a ''very'' long timescale. However, if the cosmological constant is [[Cosmological constant#Positive value|positive]], the temperature will asymptote to a non-zero positive value, and the universe will approach a state of maximum [[entropy]] in which no further [[Work (thermodynamics)|work]] is possible.<ref>
{{Cite journal
|last1         = Dyson
|first1        = Lisa
|author-link  = Lisa Dyson
|last2        = Kleban
|first2       = Matthew
|author-link2 = Matthew Kleban
|last3        = Susskind
|first3       = Leonard
|author-link3 = Leonard Susskind
|date         = 12 November 2002
|title        = Disturbing Implications of a Cosmological Constant
|journal      = [[Journal of High Energy Physics]]
|volume       = 2002
|issue        = 10
|page        = 011
|doi          = 10.1088/1126-6708/2002/10/011
|bibcode        = 2002JHEP...10..011D
|arxiv        = hep-th/0208013
|s2cid = 2344440
}}</ref>

== Time frame for heat death ==
{{Main|Future of an expanding universe}}

The theory suggests that from the "[[Big Bang]]" through the present day, [[matter]] and [[dark matter]] in the universe are thought to have been concentrated in [[star]]s, [[Galaxy|galaxies]], and [[galaxy cluster]]s, and are presumed to continue to do so well into the future. Therefore, the universe is not in [[thermodynamic equilibrium]], and objects can do physical work.<ref name="A dying universe">
{{Cite journal
| last1         = Adams
| first1        = Fred C.
| author-link  = Fred Adams
| last2        = Laughlin
| first2       = Gregory
| author-link2 = Gregory P. Laughlin
| year         = 1997
| title        = A dying universe: the long-term fate and evolution of astrophysical objects
| journal      = [[Reviews of Modern Physics]]
| volume       = 69
| issue        = 2
| pages        = 337–72
|arxiv         = astro-ph/9701131
|bibcode       = 1997RvMP...69..337A
|doi           = 10.1103/RevModPhys.69.337
| s2cid = 12173790
}}</ref><sup>:§VID</sup> The decay time for a [[supermassive black hole]] of roughly 1 galaxy mass (10<sup>11</sup>&nbsp;[[solar mass]]es) because of Hawking radiation is in the order of [[googol|10<sup>100</sup>]]&nbsp;years,<ref name="page">
See in particular equation (27) in {{Cite journal
| last        = Page
| first       = Don N.
| author-link = Don Page (physicist)
| date        = 15 January 1976
| title       = Particle emission rates from a black hole: Massless particles from an uncharged, nonrotating hole
| journal     = [[Physical Review D]]
| volume      = 13
| issue       = 2
| pages       = 198–206
| bibcode     = 1976PhRvD..13..198P
| doi         = 10.1103/PhysRevD.13.198
}}</ref> so entropy can be produced until at least that time. Some large [[black hole]]s in the universe are predicted to continue to grow up to perhaps 10<sup>14</sup> {{solar mass}} during the collapse of [[supercluster]]s of galaxies. Even these would evaporate over a timescale of up to 10<sup>106</sup> years.<ref>
{{Cite journal
| last    = Frautschi
| first   = Steven
| date    = 13 August 1982
| title   = Entropy in an Expanding Universe
| url     = http://www.informationphilosopher.com/solutions/scientists/layzer/Frautschi_Science_1982.pdf
| journal = [[Science (journal)|Science]]
| volume  = 217
| issue   = 4560
| pages   = 593–9
| jstor   = 1688892
| quote   = Since we have assumed a maximum scale of gravitational binding—for instance, superclusters of galaxies—black hole formation eventually comes to an end in our model, with masses of up to 10<sup>14</sup>{{solar mass}} ... the timescale for black holes to radiate away all their energy ranges ... to 10<sup>106</sup> years for black holes of up to 10<sup>14</sup>{{solar mass}}
| bibcode = 1982Sci...217..593F
| doi     = 10.1126/science.217.4560.593
| pmid    = 17817517
| s2cid = 27717447
}}</ref> After that time, the universe enters the so-called [[future of an expanding universe#Dark Era and Photon Age|Dark Era]] and is expected to consist chiefly of a dilute gas of [[photon]]s and [[lepton]]s.<ref name="A dying universe" /><sup>:§VIA</sup> With only very diffuse matter remaining, activity in the universe will have tailed off dramatically, with extremely low energy levels and extremely long timescales. Speculatively, it is possible that the universe may enter a second [[inflation (cosmology)|inflationary]] epoch, or assuming that the current [[Quantum vacuum state|vacuum state]] is a [[False vacuum decay|false vacuum]], the vacuum may decay into a lower-[[Energy level|energy state]].<ref name="A dying universe" /><sup>:§VE</sup> It is also possible that entropy production will cease and the universe will reach heat death.<ref name="A dying universe" /><sup>:§VID</sup>

It is suggested that, over vast periods of time, a spontaneous [[entropy]] ''decrease'' would eventually occur via the [[Poincaré recurrence theorem]],<ref>{{Cite journal|last=Poincaré|first=Henri|date=1890|title=Sur le problème des trois corps et les équations de la dynamique.|journal=Acta Mathematica|volume=13|pages=A3–A270}}</ref> [[thermal fluctuations]],<ref>
{{Cite journal |last=Tegmark |first=Max |author-link=Max Tegmark |year=2003 |title=Parallel Universes |journal=[[Scientific American]] |volume=288 |issue=2003 |pages=40–51 |arxiv=astro-ph/0302131 |bibcode=2003SciAm.288e..40T |doi=10.1038/scientificamerican0503-40 |pmid=12701329}}</ref><ref>
{{Cite journal
| last        = Tegmark
| first       = Max
| date        = May 2003
| author-link = Max Tegmark
| title       = Parallel Universes
| journal     = [[Scientific American]]
| volume      = 288
| issue       = 5
| pages       = 40–51
| arxiv       = astro-ph/0302131
| bibcode     = 2003SciAm.288e..40T
| doi         = 10.1038/scientificamerican0503-40
| pmid = 12701329
}}</ref><ref>
{{Cite journal
| last1   = Werlang
| first1  = T.
| last2   = Ribeiro
| first2  = G. A. P.
| last3   = Rigolin
| first3  = Gustavo
| year    = 2013
| title   = Interplay between quantum phase transitions and the behavior of quantum correlations at finite temperatures.
| journal = [[International Journal of Modern Physics B]]
| volume  = 27
| issue   = 1n03
| page   = 1345032
| arxiv   = 1205.1046
| bibcode = 2013IJMPB..2745032W
| doi     = 10.1142/S021797921345032X
| s2cid = 119264198
}}</ref> and [[fluctuation theorem]].<ref>
{{Cite arXiv
| title     = Spontaneous entropy decrease and its statistical formula
| author    = Xiu-San Xing
| date      = 1 November 2007
| eprint     = 0710.4624
| class     =cond-mat.stat-mech
}}</ref><ref>
{{Cite journal
| last    = Linde
| first   = Andrei
| year    = 2007
| title   = Sinks in the landscape, Boltzmann brains and the cosmological constant problem
| journal = [[Journal of Cosmology and Astroparticle Physics]]
| volume  = 2007
| issue   = 1
| page   = 022
| arxiv   = hep-th/0611043
| bibcode = 2007JCAP...01..022L
| doi     = 10.1088/1475-7516/2007/01/022
| citeseerx   = 10.1.1.266.8334
| s2cid = 16984680
}}</ref> Through this, another universe could possibly be created by random [[quantum fluctuation]]s or [[quantum tunnelling]] in roughly <math>10^{10^{10^{56}}}</math> years.<ref>
{{Cite arXiv
| eprint = hep-th/0410270
| first1 = Sean M.
| last1  = Carroll
| first2 = Jennifer
| last2  = Chen
| title  = Spontaneous Inflation and Origin of the Arrow of Time
| date   = October 2004
}}{{bibcode|2004hep.th...10270C}}
</ref>

==Opposing views==
[[Max Planck]] wrote that the phrase "entropy of the universe" has no meaning because it admits of no accurate definition.<ref>
{{Cite book
| title         = Entropy (Princeton Series in Applied Mathematics)
| last          = Uffink
| first         = Jos
| publisher     = Princeton University Press
| year          = 2003
| isbn          = 978-0-691-11338-8
| editor-last   = Greven
| editor-first  = Andreas
| editor-last2  = Warnecke
| editor-first2 = Gerald
| editor-last3  = Keller
| editor-first3 = Gerhard
| page         = 129
| chapter       = Irreversibility and the Second Law of Thermodynamics
| quote         = The importance of Planck's Vorlesungen über Thermodynamik (Planck 1897) can hardly be [over]estimated. The book has gone through 11 editions, from 1897 until 1964, and still remains the most authoritative exposition of classical thermodynamics.
}}</ref><ref>
{{Cite book |last=Planck |first=Max |url=https://archive.org/stream/treatiseonthermo00planrich#page/100/mode/2up |title=Treatise on Thermodynamics |publisher=Longmans, Green |year=1903 |location=London |page=101 |translator-last=Ogg |translator-first=Alexander |author-link=Max Planck}}</ref> In 2008, Walter Grandy wrote: "It is rather presumptuous to speak of the entropy of a universe about which we still understand so little, and we wonder how one might define thermodynamic entropy for a universe and its major constituents that have never been in equilibrium in their entire existence."<ref>
{{Cite book
| title     = Entropy and the Time Evolution of Macroscopic Systems
| last      = Grandy
| first     = Walter T. Jr.
| publisher = Oxford University Press
| year      = 2008
| isbn      = 978-0-19-954617-6
| page      = 151
| url       = https://books.google.com/books?id=SnMF37J50DgC
}}</ref> According to [[László Tisza]], "If an isolated system is not in equilibrium, we cannot associate an entropy with it."<ref>
{{Cite book
| title       = Generalized Thermodynamics
| last        = Tisza
| first       = László
| author-link = László Tisza
| publisher   = MIT Press
| year        = 1966
| isbn        = 978-0-262-20010-3
| page       = 41
}}</ref> [[Hans Adolf Buchdahl]] writes of "the entirely unjustifiable assumption that the universe can be treated as a closed thermodynamic system".<ref>
{{Cite book
| title       = The Concepts of Classical Thermodynamics
| last        = Buchdahl
| first       = H. A.
| publisher   = Cambridge University Press
| year        = 1966
| isbn        = 978-0-521-11519-3
| page       = 97
| author-link = Hans Adolf Buchdahl
}}</ref> According to [[Giovanni Gallavotti]], "there is no universally accepted notion of entropy for systems out of equilibrium, even when in a stationary state".<ref>
{{Cite book
| title       = Statistical Mechanics: A Short Treatise
| last        = Gallavotti
| first       = Giovanni
| publisher   = Springer
| year        = 1999
| isbn        = 978-3-540-64883-3
| page        = 290
| author-link = Giovanni Gallavotti
}}</ref> Discussing the question of entropy for non-equilibrium states in general, [[Elliott H. Lieb]] and [[Jakob Yngvason]] express their opinion as follows: "Despite the fact that most physicists believe in such a nonequilibrium entropy, it has so far proved impossible to define it in a clearly satisfactory way."<ref>
{{Cite book |last1=Lieb |first1=Elliott H. |title=Entropy |series=Princeton Series in Applied Mathematics |last2=Yngvason |first2=Jakob |publisher=Princeton University Press |year=2003 |isbn=978-0-691-11338-8 |editor-last=Greven |editor-first=Andreas |page=190 |chapter=The Entropy of Classical Thermodynamic |author-link=Elliott H. Lieb |author-link2=Jakob Yngvason |editor-last2=Warnecke |editor-first2=Gerald |editor-last3=Keller |editor-first3=Gerhard}}</ref> In Peter Landsberg's opinion: "The ''third'' misconception is that thermodynamics, and in particular, the concept of entropy, can without further enquiry be applied to the whole universe. ... These questions have a certain fascination, but the answers are speculations."<ref>
{{Cite book
| title     = Thermodynamics with Quantum Statistical Illustrations
| last      = Landsberg
| first     = Peter Theodore
| publisher = Interscience Publishers
| year      = 1961
| isbn      = 978-0-470-51381-1
| edition   = First
| page     = 391
}}</ref>

A 2010 analysis of entropy states, "The entropy of a general gravitational field is still not known", and "gravitational entropy is difficult to quantify". The analysis considers several possible assumptions that would be needed for estimates and suggests that the [[observable universe]] has more entropy than previously thought. This is because the analysis concludes that supermassive black holes are the largest contributor.<ref>
{{Cite journal
| last1            = Egan
| first1           = Chas A.
| last2            = Lineweaver
| first2           = Charles H.
| title            = A Larger Estimate of the Entropy of the Universe
| journal          = [[The Astrophysical Journal]]
| publication-date = 3 February 2010
| volume           = 710
| issue            = 2
| pages            = 1825–34 [1826]
| arxiv            = 0909.3983
| bibcode          = 2010ApJ...710.1825E
| doi              = 10.1088/0004-637X/710/2/1825
| year             = 2010
| s2cid            = 1274173
}}</ref> [[Lee Smolin]] goes further: "It has long been known that gravity is important for keeping the universe out of thermal equilibrium. Gravitationally bound systems have negative specific heat—that is, the velocities of their components increase when energy is removed. ... Such a system does not evolve toward a homogeneous equilibrium state. Instead it becomes increasingly structured and heterogeneous as it fragments into subsystems."<ref>
{{Cite journal
| last        = Smolin
| first       = Lee
| author-link = Lee Smolin
| year        = 2014
| title       = Time, laws, and future of cosmology
| journal     = [[Physics Today]]
| volume      = 67
| issue       = 3
| pages       = 38–43 [42]
| bibcode     = 2014PhT....67c..38S
| doi         = 10.1063/pt.3.2310
}}</ref> This point of view is also supported by the fact of a recent{{when|date=October 2022}} experimental discovery of a stable non-equilibrium steady state in a relatively simple closed system. It should be expected that an isolated system fragmented into subsystems does not necessarily come to thermodynamic equilibrium and remain in non-equilibrium steady state. Entropy will be transmitted from one subsystem to another, but its production will be zero, which does not contradict the [[second law of thermodynamics]].<ref>
{{Cite journal
| last1            = Lemishko
| first1           = Sergey S.
| last2            = Lemishko
| first2           = Alexander S.
|title             = Cu2+/Cu+ Redox Battery Utilizing Low-Potential External Heat for Recharge
| journal          = [[The Journal of Physical Chemistry C]]
| publication-date =  30 January 2017
| volume           = 121
| issue            = 6
| pages            = 3234–3240
| doi              = 10.1021/acs.jpcc.6b12317
| year             = 2017
}}</ref><ref>
{{Cite journal
| last1            = Lemishko
| first1           = Sergey S.
| last2            = Lemishko
| first2           = Alexander S.
|title             = Non-equilibrium steady state in closed system with reversible reactions: Mechanism, kinetics and its possible application for energy conversion
| journal          = [[Results in Chemistry]]
| publication-date = 8 February 2020
| volume           = 2
| doi              = 10.1016/j.rechem.2020.100031
| year             = 2020
| page             = 100031
| doi-access       = free
}}</ref>

==In popular culture==
{{no footnotes|section|date=November 2023}}
In Isaac Asimov's 1956 short story ''[[The Last Question]]'', humans repeatedly wonder how the heat death of the universe can be avoided.

In the 1981 ''Doctor Who'' story "[[Logopolis]]", the Doctor realizes that the Logopolitans have created vents in the universe to expel heat build-up into other universes—"Charged Vacuum Emboitments" or "CVE"—to delay the demise of the universe. The Doctor unwittingly travelled through such a vent in "[[Full Circle (Doctor Who)|Full Circle]]".

In the 1995 computer game ''[[I Have No Mouth, and I Must Scream (video game)|I Have No Mouth, and I Must Scream]]'', based on [[Harlan Ellison]]'s [[I Have No Mouth, and I Must Scream|short story of the same name]], it is stated that AM, the malevolent supercomputer, will survive the heat death of the universe and continue torturing its immortal victims to eternity.

In the 2011 anime series ''[[Puella Magi Madoka Magica]]'', the antagonist [[Kyubey]] reveals he is a member of an alien race who has been creating [[magical girls]] for millennia in order to harvest their energy to combat entropy and stave off the heat death of the universe.

In the last act of ''[[Final Fantasy XIV: Endwalker]]'', the player encounters an alien race known as the Ea who have lost all hope in the future and any desire to live further, all because they have learned of the eventual heat death of the universe and see everything else as pointless due to its probable inevitability.

The overarching plot of the ''[[Xeelee Sequence]]'' concerns the Photino Birds' efforts to accelerate the heat death of the universe by accelerating the rate at which stars become white dwarves.

The 2019 hit indie video game ''[[Outer Wilds]]'' has several themes grappling with the idea of the heat death of the universe, and the theory that the universe is a cycle of big bangs once the previous one has experienced a heat death.

In "Singularity Immemorial",<ref>{{Cite web |title=PNC Story - IOP Wiki |url=https://iopwiki.com/wiki/PNC_Story#Chapter_12:_Singularity_Immemorial |access-date=2024-09-11 |website=iopwiki.com}}</ref> the seventh main story event of the mobile game ''[[Girls' Frontline: Neural Cloud]]'', the plot is about a virtual sector made to simulate space exploration and the threat of the heat death of the universe. The simulation uses an imitation of Neural Cloud's virus entities known as the Entropics as a stand in for the effects of a heat death.

==See also==
* {{Annotated link|Arrow of time}}
* {{Annotated link|Big Bang}}
* {{Annotated link|Big Bounce}}
* {{Annotated link|Big Crunch}}
* {{Annotated link|Big Rip}}
* {{Annotated link|Chronology of the universe}}
* {{Annotated link|Cyclic model}}
* {{Annotated link|Entropy as an arrow of time|Entropy (arrow of time)}}
* {{Annotated link|Fluctuation theorem}}
* {{Annotated link|Heat death paradox}}
* {{Annotated link|The Last Question|''The Last Question''}}
* {{Annotated link|Timeline of the far future}}
* {{Annotated link|Orders of magnitude (time)}}
* {{Annotated link|Thermodynamic temperature}}
* {{Annotated link|Ultimate fate of the universe}}
* {{Annotated link|Zero-energy universe}}

== References ==
{{Reflist|30em}}

{{Big Bang timeline}}

{{Global catastrophic risks}}

{{Portal bar|Astronomy|Stars|Spaceflight|Outer space|Solar System}}

{{Authority control}}

[[Category:Ultimate fate of the universe]]
[[Category:Thermodynamic entropy]]
[[Category:1851 in science]]