Re: Entropy, Objectivity, and Timescales

[DSCHROEDER@cc.weber.edu]

This may (or may not) be my last reply to Leigh.  It's mostly 
a general comment about philosophical attitudes.  After calling
himself a "reductionist positivist realist ... " (sorry I can't 
remember it all) in a previous post, Leigh now says that entropy
"does not have an independent existence".  More fully,

> You have (in the words of the late Bill Burke) committed the sin of
> reification! (Note how well the vocabulary of religion fits this.)
> You have treated an idea (a formula) as a thing. Entropy is not a
> thing any more than energy is. It is an attribute of a system which
> "has to be computed"; it does not have an independent existence. In
> the words of Feynman "there are no blocks". 

Of course I'm quite familiar with Feynman's parable of the blocks,
and I have used it often in my teaching.  But I don't interpret it
as rigidly as you seem to.  I am reminded of the following passages
from another atheist reductionist realist, Steven Weinberg (which
I quote not because I consider Weinberg an authority, but just
because he says it better than I can):

"When we say that a thing is real we are simply expressing a sort
of respect.  We mean that the thing must be taken seriously because
it can affect us in ways that are not entirely in our control....
As a physicist I perceive scientific explanations and laws as 
things that are what they are and cannot be made up as I go along...
and I therefore accord the laws of nature (to which our present laws
are an approximation) the honor of being real."  (Dreams of a Final
Theory, page 46.)

In another passage Weinberg explains that a scientific explanation
is more than just a logical deduction:

"Talk of more fundamental truths makes philosophers nervous....
But scientists would be in a bad way if they had to limit themselves
to notions that had been satisfactorily formulated by philosophers.
No working physicist doubts that Newton's laws are more fundamental
than Kepler's or that Einstein's theory of photons is more fundamental
than Planck's theory of heat radiation."  (Page 27.)

And I would add, that Boltzmann's statistical explanation of entropy
is more fundamental than the original formula of Clausius.
(Weinberg discusses the relation of thermodynamics to statistical
mechanics a few pages later, concluding "even though thermodynamics
has been explained in terms of particles and forces, it continues
to deal with emergent concepts like temperature and entropy that
lose all meaning on the level of individual particles".)

Personally I find it incredibly useful to think of both energy and
entropy as physical substances, fluids that flow from one object
to another.  I know this model is fundamentally wrong.  I don't care.  
I still think it's useful, at least for my weak mind which needs such 
crutches.  I know the limitations of these models and when necessary 
I can use more sophisticated ideas.

But at a more fundamental level, there's a huge difference between
energy and entropy.  Energy seems to be at the root of the laws
of microscopic physics, the fundamental principles governing the
four forces.  (We write these laws in terms of Lagrangians, basically
a fancy way of talking about energy.)  Entropy, on the other hand,
completely disappears at the microscopic level.  In this sense it's a 
subjective quantity, useful only to macroscopic observers.  Perhaps
someday we'll discover that energy is also subjective in a similar
way, but this hasn't happened yet.

I'm not sure exactly which of these comments (if any) Leigh would
agree with and which he would disagree with.  But philosophical 
attitudes toward physics are pretty slippery:  there seems to be
a wide gray area between agreement and disagreement.  So I'm not
trying to argue with Leigh here, I'm just trying to say (and quote)
some things that sound good to me.

-dan