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Arrow of time
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=== Thermodynamic arrow of time === {{Main|Entropy as an arrow of time}} The arrow of time is the "one-way direction" or "asymmetry" of time. The thermodynamic arrow of time is provided by the [[second law of thermodynamics]], which says that in an isolated system, entropy tends to increase with time. Entropy can be thought of as a measure of microscopic disorder; thus the second law implies that time is asymmetrical with respect to the amount of order in an isolated system: as a system advances through time, it becomes more statistically disordered. This asymmetry can be used empirically to distinguish between future and past, though measuring entropy does not accurately measure time. Also, in an open system, entropy can decrease with time. An interesting thought experiment would be to ask: "if entropy was increased in an open system, would the arrow of time flip in polarity and point towards the past." [citation required] British physicist [[Brian Pippard|Sir Alfred Brian Pippard]] wrote: "There is thus no justification for the view, often glibly repeated, that the Second Law of Thermodynamics is only statistically true, in the sense that microscopic violations repeatedly occur, but never violations of any serious magnitude. On the contrary, no evidence has ever been presented that the Second Law breaks down under any circumstances."<ref>A. B. Pippard, Elements of Classical Thermodynamics for Advanced Students of Physics (1966), p. 100.</ref> However, there are a number of [[paradox]]es{{which|date=June 2023}} regarding [[second law of thermodynamics#Irreversibility|violation of the second law of thermodynamics]], one of them due to the [[Poincaré recurrence theorem]]. This arrow of time seems to be related to all other arrows of time and arguably underlies some of them, with the exception of the [[#Particle physics (weak) arrow of time|weak arrow of time]].{{clarify|date=April 2019|reason=anchor lost results in unhelpful self-reference, clarification of the weak arrow is needed}} [[Harold F. Blum|Harold Blum]]'s 1951 book ''Time's Arrow and Evolution''<ref name="Blum1951">{{cite book|last=Blum|first=Harold F.|author-link=Harold F. Blum|title=Time's Arrow and Evolution|url=https://books.google.com/books?id=tmcNnwEACAAJ|edition=First|year=1951|publisher=Princeton University Press |isbn=978-0-691-02354-0}}</ref> discusses "the relationship between time's arrow (the second law of thermodynamics) and [[organic evolution]]." This influential text explores "[[irreversibility]] and direction in evolution and order, [[negentropy]], and [[evolution]]."<ref name=arrow-review>{{cite journal | doi = 10.1016/0019-1035(69)90059-1 | title= Book review: Time's arrow and evolution: Third Edition | journal = Icarus | volume = 11 | issue = 2 | pages = 278–279 | last = Morowitz | first = Harold J. | date = September 1969|bibcode = 1969Icar...11..278M | pmc = 2599115 }}</ref> Blum argues that evolution followed specific patterns predetermined by the [[inorganic chemistry|inorganic]] nature of the earth and its thermodynamic processes.<ref name=yale>{{cite journal | pmc = 2599115 | title= Book reviews: Time's Arrow and Evolution | journal = [[Yale Journal of Biology and Medicine]] | volume = 24 | issue = 2 | pages = 164 | last = McN. | first = W. P. | date = November 1951}}</ref>
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