Past hypothesis

In cosmology, the past hypothesis is a fundamental law of physics that postulates that the universe started in a low entropy state.[1] The second law of thermodynamics indicates that the entropy increases in time. Extrapolating this idea to the universe, in order to have a global arrow of time, the hypothesis argues that the universe must have started from a special event with lower entropy in order to evolve and observe an increase of entropy.

This idea has been discussed since the development of statistical mechanics,[Note 1] but the term past hypothesis was coined by philosopher David Albert in 2000.[2][3] Philosophical and theoretical efforts focus on trying to explain the consistency and the origin of this postulate.[4]

Common theoretical frameworks have been developed in order to explain the origin of the past hypothesis based on inflationary models or the anthropic principle.[1][2] The Weyl curvature hypothesis, an alternative model by Roger Penrose, argues a link between entropy, the arrow of time and the curvature of spacetime (encoded in the Weyl tensor).[2][5]

See also

Notes
  1. See Ludwig Boltzmann Vorlesungen über Gastheorie ("Lectures on Gas Theory", 1896)

References
  1. Callender, Craig (2011-04-07). The Oxford Handbook of Philosophy of Time. Oxford University Press. ISBN 978-0-19-161724-9.
  2. Ainsworth, Peter Mark (2008). "Cosmic inflation and the past hypothesis". Synthese. 162 (2): 157–165. doi:10.1007/s11229-007-9179-4. ISSN 0039-7857. S2CID 33523028.
  3. Albert, David Z. (2009-06-30). Time and Chance. Harvard University Press. ISBN 978-0-674-26138-9.
  4. Falk, Dan (2016-07-19). "A Debate Over the Physics of Time". Quanta Magazine. Retrieved 2022-02-27.
  5. R., Penrose (1979). "Singularities and time-asymmetry". {{cite journal}}: Cite journal requires |journal= (help)
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