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| No reason for entropy reversal ArgumentOpposé1 #106948 There is no good reason to suppose that the entropy gradient will reverse and entropy decrease during the collapsing phase of the cycle. It would be extremely improbable for this to happen for just the reasons Boltzmann outlined in his statistical explanation of the Second Law. | |
+Citations (2) - CitationsAjouter une citationList by: CiterankMapLink[1] From Eternity to Here (book excerpt)
En citant: Sean M. Carroll - Theoretical physicist, California Institute of Technology
Cité par: Peter Baldwin 6:31 AM 11 May 2011 GMT
Citerank: (4) 100641The Arrow of Time?A map exploring some issues concerning the nature of time that lie at the boundary of physics and philosophy. The map follows up a talk to the Blackheath Philosophy Forum on 2 April 2011 by Huw Price, Professor of Philosophy and director of the Center for Time at Sydney University.7F1CEB7, 104605Bolztmann's H-theoremIn his 'H-theorem' Boltzmann tried to formally prove that inter-molecular collisions drive gases toward equilibrium, confirming the Second Law (for gases at least). In this approach, he aimed show that it is not just overwhelmingly probable but an exceptionless law like conservation of energy.109FDEF6, 106945Cyclical universeIf we assume that the universe alternates between expanding and collapsing phases, with the entropy gradient reversing during the collapse phase, the need for a time-asymmetric boundary condition is avoided since the evolution of the universe is time-symmetric overall. 959C6EF, 107347Multiverse is a predictionThe multiverse is a prediction arising from inflationary cosmology, which can be tested.13EF597B
URL: | | Extrait - "The Gold universe never really caught on among cosmologists, for a simple reason: There's no good reason for there to be a future boundary condition of any particular sort. Sure, it restores the overall symmetry of time, but nothing we have experienced in the universe demands such a condition, nor does it follow from any other underlying principles."
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Link[2] The Cosmic Origins of Time's Arrow
En citant: Sean M. Carroll - Theoretical physicist, California Institute of Technology
Cité par: Peter Baldwin 6:30 AM 12 May 2011 GMT
Citerank: (4) 104153Why low entropy in the past?How do we account for the low entropy of the early universe reflected in the extreme - but not perfect - homogeneity of the distribution of matter and energy shortly after the Big Bang? When gravity is prominent - as in the early universe - a smooth distribution is unstable and of low entropy.8FFB597, 104159Fluctuations in de Sitter spaceCosmologist Sean Carroll has proposed that low entropy may result from fluctuations in De Sitter space - a vacuum except for dark energy and the end point of expanding space time. Some fluctuations lead to cosmological inflation, giving rise to smooth low entropy 'baby universes' - like ours.959C6EF, 107149Inflationary universeSome cosmologists claim that the inflationary cosmological theory explains the extremely smooth distribution of matter and energy - and hence low entropy - of the early universe. The extremely rapid expansion effectively smooths out any initial irregularities.959C6EF, 107150Presupposes lower entropyAs an explanation for the low initial entropy of the universe, inflationary cosmology does not work since for it to work the dark energy had to begin in an even lower entropy configuration. The puzzle is pushed back a step rather than resolved.13EF597B
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| | Extrait - "Some cosmologists imagine that the universe went through a “bounce.” Before this event, space was contracting, but instead of simply crashing to a point of infinite density, new physical principles - quantum gravity, extra dimensions, string theory or other exotic phenomena kicked in to save the day at the last minute, and the universe came out the other side into what we now perceive as the big bang. Though intriguing, bouncing cosmologies do not explain the arrow of time. Either entropy was increasing as the prior universe approached the crunch - in which case the arrow of time stretches infinitely far into the past - or the entropy was decreasing, in which case an unnatural low-entropy condition occurred in the middle of the universe’s history (at the bounce). Either way, we have again passed the buck on the question of why the entropy near what we call the big bang was small." |
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