On Tue, Jan 7, 2014 at 12:44 PM, John Clark <johnkcl...@gmail.com> wrote:
> > > > On Tue, Jan 7, 2014 at 12:00 PM, Jesse Mazer <laserma...@gmail.com> wrote: > >> >> >> >>> he assumed this time asymmetry was fundamental, not a mere >>>> statistical effect related to the low entropy of the initial conditions of >>>> the experiment. >>>> >>> >>> >> A mere statistical effect?? I would argue that the second law of >>> thermodynamics is much more fundamental than the first. The first law, the >>> idea that matter and energy can not be created or destroyed is not a >>> logical necessity it's merely a empirical observation, up to now we've just >>> never seen that law violated and we use induction to conclude that we never >>> will. Induction is a very good rule of thumb but it you wait long enough it >>> can sometimes lead you astray. I don't expect it to happen but I can at >>> least conceive of the idea that someday we will find a circumstance where >>> the first law is untrue. >>> But the second law is not like that, conceiving of a world where entropy >>> doesn't increase with time is like imagining what the world would be like >>> if 2+2=5. The second law is not based on observation but on pure logic and >>> the fact that there are just more ways to be disorganized than organized. >>> Science always changes but if I had to pick one thing that would still be >>> valid in a thousand or even a million years it would be the second law. >>> >> >> > Are you disputing the "statistical effect" part, or the "mere" part? >> > > The "mere" part. > OK, then I think we agree on most aspects of the 2nd law, except maybe for the part below: > > > I think it's going too far to say that imagining a world where entropy >> doesn't increase is like imagining a world where 2+2=5, since you do need >> *some* assumptions about the laws of physics to derive the second law. >> > > Well... you must assume that the laws of physics actually do something, > that is to say they must change something, otherwise they wouldn't be laws. > And we know that there are far more ways to be disorganized than organized, > so if you change something that is in a very organized state you will > almost certainly make it more disorganized. And that is the second law. > But as I said, you could have laws where a large number of initial states can all lead to the same final state (many cellular automata work this way, specifically all the ones whose rules are not "reversible"--for example, in the "Game of Life" there are many initial states you can choose that will lead all the black squares to eventually disappear and leave you with all white squares). Just because there are more high-entropy states than low, that isn't enough to show that the dynamics are more likely to take you to a higher-entropy than a lower-entropy state, you need some additional assumption about conservation of phase space volume (so in discrete case like a cellular automaton, the number of initial states in your statistical ensemble is always equal to the number of later states). Jesse > > > Even with the laws of physics we know, if you don't assume the universe >> *starts* in a state of low entropy, then the 2nd law should actually be >> time-symmetric >> > > Exactly. And we know that things are very very far from time-symmetric so > we can conclude that the universe *did* start in a state of low entropy. > > > see for example Sean Carroll's theory which he summarizes in a blog post >> at http://preposterousuniverse.blogspot.com/2004/10/arrow-of-time.htmland >> also in the paper linked to there, and further in his book "From >> Eternity to Here"), >> > > I believe I've read all of Sean Carroll's books and I've bought 2 of his > courses on DVD. > > John K Clark > > > > -- > 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 everything-list+unsubscr...@googlegroups.com. > To post to this group, send email to email@example.com. > Visit this group at http://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/groups/opt_out. > -- 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 everything-list+unsubscr...@googlegroups.com. To post to this group, send email to firstname.lastname@example.org. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.