Editing Heat death paradox (section)

==The paradox==
{{blockquote|Assuming that the universe is eternal, a question arises: How is it that [[thermodynamic equilibrium]] has not already been achieved?<ref name="Cucic2009b">{{cite arXiv|last1=Cucic|first1=Dragoljub A.|date=2008|title=Astrophysical Paradoxes, long version|eprint=0812.1679|class=physics.hist-ph}}</ref>}}

This theoretical paradox is directed at the then-mainstream strand of belief in a classical view of a ''[[sempiternal]]'' universe, whereby its matter is postulated as everlasting and having always been recognisably the universe. Heat death paradox is born of a paradigm resulting from fundamental ideas about the cosmos. It is necessary to change the paradigm to resolve the paradox.

The paradox was based upon the rigid mechanical point of view of the [[second law of thermodynamics]] postulated by [[Rudolf Clausius]] and [[Lord Kelvin]], according to which heat can only be transferred from a warmer to a colder object. It notes: if the universe were eternal, as claimed classically, it should already be cold and isotropic (its objects should have the same temperature, and the distribution of matter or radiation should be even).<ref name="Cucic2009b"/> Kelvin compared the universe to a clock that runs slower and slower, constantly dissipating energy in ''[[Heat|impalpable heat]]'', although he was unsure whether it would ''stop for ever'' (reach thermodynamic equilibrium). According to this model, the existence of usable energy, which can be used to perform work and produce entropy, means that the clock has not stopped - since a conversion of heat in mechanical energy (which Kelvin called a ''rejuvenating universe'' scenario) is not contemplated.<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><ref name="On the Age of the Sun's Heat"/>

According to the laws of thermodynamics, any hot object transfers heat to its cooler surroundings, until everything is at the same [[temperature]]. For two objects at the same temperature as much [[heat flow]]s from one body as flows from the other, and the net effect is no change. If the universe were infinitely old, there must have been enough time for the stars to cool and warm their surroundings. Everywhere should therefore be at the same temperature and there should either be no stars, or everything should be as hot as stars. The universe should thus achieve, or asymptotically tend to, thermodynamic equilibrium, which corresponds to a state where no [[thermodynamic free energy]] is left, and therefore no further work is possible: this is the heat death of the universe, as predicted by Lord Kelvin in 1852. The average temperature of the cosmos should also asymptotically tend to [[absolute zero|Kelvin Zero]], and it is possible that a [[maximum entropy thermodynamics|maximum entropy]] state will be reached.<ref name=Thompson2015>''[https://www.britannica.com/science/thermodynamics/Entropy-and-heat-death Laws of Thermodynamics]'' Thompson and Clausius, [[Oxford University Press]], 2015</ref>