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ISRN Thermodynamics
Volume 2012 (2012), Article ID 850957, 7 pages
Review Article

Threads of Time

1Department of Physics, University of Helsinki, 00014 Helsinki, Finland
2Department of Biosciences, University of Helsinki, 00014 Helsinki, Finland
3Institute of Biotechnology, University of Helsinki, 00014 Helsinki, Finland
4Department of Biological Sciences, Binghamton University, Binghamton, NY 13754, USA

Received 29 March 2012; Accepted 20 May 2012

Academic Editors: I. Haque and H. Hirao

Copyright © 2012 Arto Annila and Stanley Salthe. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The concept of time’s arrow is examined using the principle of least action as given in its original non-Abelian form. When every entity of nature is considered to be composed of quantized actions, such an entity will change, either by absorbing quanta from surrounding actions or by emitting quanta to the surrounding actions. In natural processes, quanta disperse from high-energy density actions to low-energy density actions in quest of consuming free energy in least time. We propose that the flux of quanta embodies the flow of time, and therefore the irreversible consumption of free energy creates time’s arrow in a fundamental physical sense. The cosmological arrow of time results from universal processes that take place, most notably, in stars and other celestial systems, where matter, that is, bound actions, combusts to photons, that is, freely propagating actions. The biological arrow of time manifests itself in maturation processes where quanta absorb to emerging functional structures, leading eventually to aging processes where quanta, on balance, emit from disintegrating organs. Mathematical analysis of an evolutionary equation of motion, given in general terms of a spontaneous symmetry breaking process of actions, reveals the reason why future paths—and the future itself—remain inherently intractable.