Re: initial entropy
Pentcho Valev
sci.physics.research:
> Hi,
>
> I am reading in the introduction of hep-th/0208013: "the low entropy
> starting point is the ultimate reason that the universe has an arrow
> of time, without which the second law would not make sense." This was
> apparently "emphasized by Penrose many years ago".
People much cleverer than Roger Penrose call the arrow-of-time
(entropy-increase) version of the second law "red herring":
http://philsci-archive.pitt.edu/archive/00000313/
JOS UFFINK: "This summary leads to the question whether it is fruitful
to see irreversibility or time-asymmetry as the essence of the second
law. Is it not more straightforward, in view of the unargued
statements of Kelvin, the bold claims of Clausius and the strained
attempts of Planck, to give up this idea? I believe that Ehrenfest-
Afanassjewa was right in her verdict that the discussion about the
arrow of time as expressed in the second law of the thermodynamics is
actually a RED HERRING."
Pentcho Valev
pva...@yahoo.com
>
> Could somebody please explain this statement, or perhaps point me to a
> useful place to look?
>
> Presumably by low entropy they simply mean that the initial conditions
> look finely tuned (very special). Of course the meaning of "special"
> or "finely tuned" is rather meaningless without a measure (the density
> of states if you will). So I guess they use the effective field theory
> intuition to describe what is tuned and what is not. Is this all?
>
> Now what does this have to do with an arrow of time and the second
> law?
>
> Let us assume the universe is describable by a conventional
> Hamiltonian and Hilbert space. Let us assume the universe started off
> in a pure state. I guess the meaning of an "arrow of time existing"
> and "the second law being true" can be loosely transcribed as "at late
> enough times the pure state looks classical" - that for late enough
> times the dynamics is well approximated by classical mechanics on
> large enough length scales. You could have imagined a state which
> never looks classical at any time, for example the, ground state of a
> double well potential. Or you could have imagined a state in which
> really funny stuff happens, like every time you flip a coin it comes
> up tails.
>
> Are they claiming that these kinds of states are far more numerous and
> far more likely? That the initial states which lead to late time
> behaviour which looks classical and in which statistical laws are
> obeyed (like a sequence 10000 coin flips will more or less give an
> equal number of head and an equal number of tails) are vastly
> outnumbered by the ones that don't?
>
> thanks,
>
> Dusan
tadchem
Leave it to a historian (Uffink) to deign to hold forth on Entropy (a
feature of statistical mechanics and thermodynamics) versus Time-
Reversibility (a feature of deterministic Cartesian systems).
The two concepts are from completely different and inherently
incompatible realms.
A clear case of elementary equivocation - apples vs oranges.
An theoretical physicist understands the difference.
Entropy applies when the exact phase space configuration and all
possible interactions are not known or controllable.
Time-Reversibility applies only when the exact phase space
configuration and all possible interactions are known.
Imagine how big would a computer have to be to program the exact
position and velocity (6 variables per particle) for all N particles
in the universe, PLUS all N^2 pairwise interactions, etc.
You cannot contain a 1:1 scale model of the universe within the
universe and have anywhere to stand to read the output. A Time-
Reversible model of the universe is unachievable.
Tom Davidson
Richmond, VA
Androcles
"tadchem" <tad...@comcast.net> wrote in message
news:4ff526a6-1a65-49a5...@34g2000hsh.googlegroups.com...
Leave it to a historian (Uffink) to deign to hold forth on Entropy (a
feature of statistical mechanics and thermodynamics) versus Time-
Reversibility (a feature of deterministic Cartesian systems).
The two concepts are from completely different and inherently
incompatible realms.
A clear case of elementary equivocation - apples vs oranges.
An theoretical physicist understands the difference.
===============================================
AN theoretical physicist is a dickhead that understands NOTHING,
by definition of "theoretical".
A clear case of elementary equivocation - theoretical vs real.
kunzmilan
> On Aug 20, 9:55 pm, Dashen <sim...@gmail.com> wrote in
> sci.physics.research:
>
> > Hi,
>
> > I am reading in the introduction of hep-th/0208013: "the low entropy
> > starting point is the ultimate reason that the universe has an arrow
> > of time, without which the second law would not make sense." This was
> > apparently "emphasized by Penrose many years ago".
>
> People much cleverer than Roger Penrose call the arrow-of-time
> (entropy-increase) version of the second law "red herring":
>
> http://philsci-archive.pitt.edu/archive/00000313/
> JOS UFFINK: "This summary leads to the question whether it is fruitful
> to see irreversibility or time-asymmetry as the essence of the second
> law. Is it not more straightforward, in view of the unargued
> statements of Kelvin, the bold claims of Clausius and the strained
> attempts of Planck, to give up this idea? I believe that Ehrenfest-
> Afanassjewa was right in her verdict that the discussion about the
> arrow of time as expressed in the second law of the thermodynamics is
> actually a RED HERRING."
>
> Pentcho Valev
> pva...@yahoo.com
>
Entropy grows with growing temperature.
Universe had its highest temperature at the start og big bang.
Temperature is the integrating factor of thermodynamical systems.
The question is, if temperature is the integrating factor of
Universe.
kunzmilan
Pentcho Valev
> Am Thu, 21 Aug 2008 07:25:09 -0700 schrieb tadchem <tadc...@comcast.net>
> in 4ff526a6-1a65-49a5-bccc-38c2bb92b...@34g2000hsh.googlegroups.com in
> sci.physics.relativity:
>
> > On Aug 21, 8:41 am, Pentcho Valev <pva...@yahoo.com> wrote:
> >> On Aug 20, 9:55 pm, Dashen <sim...@gmail.com> wrote in
> >> sci.physics.research:
> >> > I am reading in the introduction of hep-th/0208013: "the low entropy
> >> > starting point is the ultimate reason that the universe has an arrow
> >> > of time, without which the second law would not make sense." This was
> >> > apparently "emphasized by Penrose many years ago".
>
> >> People much cleverer than Roger Penrose call the arrow-of-time
> >> (entropy-increase) version of the second law "red herring":
>
> >> http://philsci-archive.pitt.edu/archive/00000313/ JOS UFFINK: "This
> >> > Now what does this have to do with an arrow of time and the second
> >> > law?
> > Leave it to a historian (Uffink) to deign to hold forth on Entropy (a
> > feature of statistical mechanics and thermodynamics) versus Time-
> > Reversibility (a feature of deterministic Cartesian systems).
>
> > The two concepts are from completely different and inherently
> > incompatible realms.
>
> would have found (§1 page 94) that Uffink agrees with you, as Pentcho
> Valev pointed out. You should have at least looked at the summary table
> (Table 1) on page 91.
>
> [...]
>
> > Entropy applies when the exact phase space configuration and all
> > possible interactions are not known or controllable.
>
> that system is known or not, or controllable or not.
How do you know the entropy is a "state variable" ("state function" is
better)? You have proved it yourself, you have verified Clausius'
proof and find it is correct, or you just repeat what textbooks
repeat?
Pentcho Valev
pva...@yahoo.com