On Fri, Aug 22, 2014 at 1:27 PM, meekerdb <meeke...@verizon.net> wrote:
> > > The second law is only approximately true for finite systems (in either > time or space). Globally it's a tautology: the arrow-of-physical-time > points in the direction of increasing entropy, whichever way you chose > coordinate time. > It's not a tautology. The second law can explain why tomorrow will almost certainly be more disordered (have a higher entropy) than today, it's just because there are astronomically (too weak a word but the best I could find) more disordered states than ordered ones. However by using the exact same logic and the fact that the state of things today evolved from the state of things yesterday and because there are astronomically more such disordered states than ordered ones we must conclude that things today almost certainly evolved from one of those very numerous disordered states that existed yesterday. So entropy was almost certainly higher yesterday than today. But that's nuts! Everybody thinks that entropy will be higher tomorrow but nobody really thinks it's true that entropy was also higher yesterday, and yet it is undeniable that you can not deduce a asymmetry in time (time's arrow) from thermodynamics or from any of the known laws of physics alone; this dichotomy is sometimes called Loschmidt's Paradox or Loschmidt's Objection. To deduce the arrow of time and get rid of Loschmidt's Paradox the laws of physics are not enough, you must make an additional assumption about initial conditions called "The Past Hypothesis", it's the assumption that the universe started out in a very very low entropy state, as low as you can go. And therefore there was only one direction it could evolve, toward a higher entropy state. John K Clark > > > The second law is wrong in the same universe that 2 +2 =5, that is to > say the same universe where logic does not hold. I do not think such a > universe exists. > > Perhaps the first law is just as fundamental as the second, perhaps not. > Right now we believe in the first law not because it would be illogical to > believe otherwise but just because so far we've never seen mass-energy > created or destroyed. I doubt it but it's not inconceivable that tomorrow > we will, but it is inconceivable that tomorrow 2+2 will be 5 or that the > second law is wrong. > > > In a general relativistic universe that's expanding there's no time-like > Killing field and so there's no canonical way to define total energy. GR > conserves stress-energy locally but in general the total is undefined. > John Baez has a nice discussion of the problem. > > Brent > > -- > 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 everything-list@googlegroups.com. > Visit this group at http://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > -- 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 everything-list@googlegroups.com. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
