Editing Arrow of time (section)

{{Short description|Concept in physics of one-way time}}
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{{Hatnote|This article is an overview of the subject. For a more technical discussion and for information related to current research, see [[Entropy (arrow of time)]].}}
{{Redirect|The Arrow of Time|the soundtrack for Timelapse of the Future|Timelapse of the Future#Soundtrack}}

[[File:Arthur Stanley Eddington.jpg|thumb|upright=0.9|[[Arthur Eddington|Sir Arthur Stanley Eddington]] (1882–1944)]]

The '''arrow of time''', also called '''time's arrow''', is the concept positing the "one-way direction" or "[[asymmetry]]" of [[time]]. It was developed in 1927 by the British astrophysicist [[Arthur Eddington]], and is an [[List of unsolved problems in physics|unsolved general physics question]]. This direction, according to Eddington, could be determined by studying the organization of [[atom]]s, [[molecule]]s, and [[Physical object|bodies]], and might be drawn upon a [[Four-dimensional space|four-dimensional]] relativistic map of the world ("a solid block of paper").<ref>{{Cite book |last=Weinert |first=Friedel |url=https://books.google.com/books?id=-R4ANHu-csMC&pg=PA143 |title=The Scientist as Philosopher: Philosophical Consequences of Great Scientific Discoveries |date=2004-11-25 |publisher=Springer Science & Business Media |isbn=978-3-540-21374-1 |page=143 |language=en}}</ref>

The arrow of time paradox was originally recognized in the 1800s for gases (and other substances) as a discrepancy between [[microscopic]] and [[macroscopic]] description of [[thermodynamics]] / [[statistical physics]]: at the [[microscopic]] level physical processes are believed to be either entirely or mostly [[T-symmetry|time-symmetric]]: if the direction of time were to reverse, the theoretical statements that describe them would remain true. Yet at the [[macroscopic]] level it often appears that this is not the case: there is an obvious direction (or ''flow'') of time.