>If instead in the first instant of time the universe was in a very high >entropy state then in the second instant Entropy could have been >smaller or larger with about equal probability and there would be no >second law of thermodynamics and time would have no arrow.
> I say "almost" because there are some ways around it. If the universe > recontracts the AoT will probably continue to point toward the Big Crunch The arrow of time is defined by the increase of entropy because that is the only direction in which life can operate. http://es.slideshare.net/agcorona1/arrow-of-time-determined-by-lthe-easier-direction-of-computation-for-life Then if there are observers, they live in the direction of entropy increase. and they create the notion of "beginning" as the location in space-time where entropy was the lowest. That notion of beginning that only has meaning for a being living in time. Then it is redundant to say that the beginning was a state of low entropy. 2014-11-08 5:14 GMT+01:00 LizR <[email protected]>: > On 8 November 2014 16:53, John Clark <[email protected]> wrote: > >> On Thu, Nov 6, 2014 at 3:56 PM, meekerdb <[email protected]> wrote: >> >> > I'd say that expansion of the universe is almost necessary, not >>> contingent. >>> >> >> I'd say that by about 1850 when people started to have a understanding of >> what Entropy was physicists had all they needed to have known that the >> universe must have started out in a very very low entropy state, that is to >> say they could have predicted the Big Bang in the early to mid 19th >> century; and they wouldn't have needed to go near a telescope to do so. But >> unfortunately they didn't, it's one of the great failures of nerve or >> imagination in the history of science. >> > > Another feature of the big bang / expanding universe is that it > continually raises the entropy ceiling (maxium entropy that can exist in a > given volume). > >> >> > The AoT has to point in the direction of entropy increase >>> >> >> But the question is WHY does time point in the direction of entropy >> increase. The answer is because in the first instant of time the universe >> was in a extraordinarily low entropy state, probably as low as it could >> get, and because there are vastly more disordered (high entropy) states >> than ordered (low entropy) states. So regardless of what the laws of >> physics were by the second instant of time the chances are overwhelming >> that entropy will be higher than it was at the first instant. >> > > The universe could potentially start in a state of maximum entropy (at > least in terms of the equilibrium of mass-energy) and still move to states > where things can happen (if there are *any* inhomogeneities). > Gravitational entropy is trickier, as it would tend to indicate the > universe should start as a black hole (although that would never actually > start...) But the rest of the AOT can be handled by the entropy ceiling > being continually raised, almost regardless of initial conditions. > >> >> If instead in the first instant of time the universe was in a very high >> entropy state then in the second instant Entropy could have been smaller or >> larger with about equal probability and there would be no second law of >> thermodynamics and time would have no arrow. >> >> > I say "almost" because there are some ways around it. If the universe >>> recontracts the AoT will probably continue to point toward the Big Crunch >>> >> >> Even if that were true time would still have a arrow, it would just be >> pointing in the opposite direction we are accustomed to. But why should >> time have a preferred direction at all? The laws of physics alone can not >> explain it nor is there any reason to expect that they should. Even if you >> know all the laws of physics there is to know you still can't predict what >> a system is going to do tomorrow unless you know what state it is in today; >> you've got to know the initial conditions. The laws of physics can explain >> why Entropy will be higher tomorrow than today, but it can't explain why it >> was lower yesterday than today, for that you need initial conditions. >> >> True, although (see above) I think we can sneak around requiring any > "implausibly low entropy starting conditions". > > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > -- Alberto. -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
