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| Why do we see an entropy gradient? Question1 #103810 We find ourselves in an observable universe in which entropy increases consistently in one direction, thereby showing time asymmetry - an arrow of time. Yet the vast majority of underlying dynamical processes are time-symmetric. How to account for this? Two broad approaches are considered here. | Note that the important issue is not whether we regard the entropy slope as positive or negative. If it is a matter of convention which direction counts as 'positive' time, then it follows that whether entropy is regarded as increasing or decreasing is likewise a matter of convention (see citation below). |
+Citations (2) - CitationsAjouter une citationList by: CiterankMapLink[1] Time’s Arrow and Eddington’s Challenge
En citant: Huw Price - Head of the Center for Time, University of Sydney
Publication date: 2010
Cité par: Peter Baldwin 0:53 AM 15 April 2011 GMT
Citerank: (6) 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, 103807The experience of timeThis branch of the map considers the phenomenology of time - the various ways in which time presents itself directly to our consciousness. Why do we think time has the features indicated by the passage view? The answers will hopefully enable us to connect the phenomenological to the physical.8FFB597, 103810Why do we see an entropy gradient?We find ourselves in an observable universe in which entropy increases consistently in one direction, thereby showing time asymmetry - an arrow of time. Yet the vast majority of underlying dynamical processes are time-symmetric. How to account for this? Two broad approaches are considered here.8FFB597, 104152Past hypothesisWe inhabit a universe - or part thereof - characterized by a low-entropy past that has enabled the evolution of intelligent observers to occur. This together with Boltzmann's probabilistic argument (see sibling node) implies entropy will increase over time toward thermal equilibrium.109FDEF6, 104155Boltzmann-Schuetz hypothesisBoltzmann and Schuetz claimed that in a universe that is near thermal equilibrium, and given sufficient time, there will be regions where there is a temporary deviation into a low entropy state, from which it will trend back to equilibrium. Anthropic selection accounts for us being in such a region.959C6EF, 105365Anti-matter objectionIf the time-asymmetry of thermodynamics were associated with the symmetry violation of the neutral K meson (neutral Kaon) then anti-matter would show the reverse of the normal thermodynamic asymmetry AND no such anti-matter reversal is apparent.13EF597B
URL: | | Extrait - "By the end of the nineteenth century, on the shoulders of Maxwell, Boltzmann and many lesser giants, physics had realised that there is a deep puzzle behind the familiar phenomena described by the new science of thermodynamics. On the one hand, many such phenomena show a striking temporal bias. They are common in one temporal orientation, but rare or non-existent in reverse. On the other hand, the underlying laws of mechanics show no such temporal preference. If they allow a process in one direction, they also allow its temporal mirror image. Hence the puzzle : if the laws are so even-handed, why are the phenomema themselves so one-sided ?" |
Link[2] Entropy gradient not entropy increase
En citant: Huw Price - Head of the Center for Time, University of Sydney
Cité par: Peter Baldwin 1:40 AM 2 May 2011 GMT
Citerank: (6) 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, 103807The experience of timeThis branch of the map considers the phenomenology of time - the various ways in which time presents itself directly to our consciousness. Why do we think time has the features indicated by the passage view? The answers will hopefully enable us to connect the phenomenological to the physical.8FFB597, 103810Why do we see an entropy gradient?We find ourselves in an observable universe in which entropy increases consistently in one direction, thereby showing time asymmetry - an arrow of time. Yet the vast majority of underlying dynamical processes are time-symmetric. How to account for this? Two broad approaches are considered here.8FFB597, 104152Past hypothesisWe inhabit a universe - or part thereof - characterized by a low-entropy past that has enabled the evolution of intelligent observers to occur. This together with Boltzmann's probabilistic argument (see sibling node) implies entropy will increase over time toward thermal equilibrium.109FDEF6, 104155Boltzmann-Schuetz hypothesisBoltzmann and Schuetz claimed that in a universe that is near thermal equilibrium, and given sufficient time, there will be regions where there is a temporary deviation into a low entropy state, from which it will trend back to equilibrium. Anthropic selection accounts for us being in such a region.959C6EF, 105365Anti-matter objectionIf the time-asymmetry of thermodynamics were associated with the symmetry violation of the neutral K meson (neutral Kaon) then anti-matter would show the reverse of the normal thermodynamic asymmetry AND no such anti-matter reversal is apparent.13EF597B
URL: | | Extrait - "If it is conventional which direction counts as positive time, then it is also conventional whether entropy increases or decreases. It increases by the lights of the usual convention, but decreases if we reverse the labelling. But this may seem ridiculous. Doesn't it imply, absurdly, that the thermodynamic asymmetry is merely conventional ?
No. The crucial point is that while it's a conventional matter whether the entropy gradient slopes up or down, the gradient itself is objective. The puzzling asymmetry is that the gradient is monotonic it slopes in the same direction everywhere (so far as we know)."
p.121 |
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