RE: [pf] entropy.

by David A

11 December 2000 22:07 UTC

David MacClement wrote:
> · For one thing, I see the comments as dealing with the 
> puzzling examples in the last half of my post, and mainly I believe > 
> he's addressing the question of "being sure": being able to measure > 
> the entropy and being sure it is increasing or staying the same.

No, I'm talking about general principles based on the 2nd law of 
thermodynamics. If an isolated system undergoes changes, it will change 
in such a way that its entropy will not decrease. 

> · /I/ don't think entropy (either the amount, known or not, or 
> the concept) disappears as soon as some energy goes in or out of 
> a bounded system.

Yes, the concept remains, but if the system is not isolated, you cannot 
a priori state whether the entropy increases, decreases, or stays the 
same. It may do any of these. None of the systems you've mentioned are 
isolated systems. A refrigerator decreases the entropy of the water you 
put in the ice cube trays, but overall it increases the entropy of the 
universe. 
 
> · So I'm still interested in other people's ideas, at least on 
> what I said in the first half of the note. I admit that applying 
> one aspect of entropy to philosophy may be a mistake (though I 
> don't think so), but doing that has brought such a surprising amount > 
> of clarity to my thinking that I thought others might want to > consider 
> it too.

Statistically, entropy is proportional to the log of the number of 
energy states available to a system. For things like cells this number 
is huge and essentially unknown. Is it really a priori clear that a cell 
has less energy states than its dissembled atoms? 

Similar with the mining of any mineral. The system is just so incredibly 
complicated that taking account of entropy changes is impossible. And 
so, it seems to me, making arguments based on assumptions about entropy 
changes can't lead to any solid conclusions.

> For me this has been the main reason I've been concerned 
> about "running out of resources"; not that there will be less and 
> less availability of those resources for human use, but that humans > 
> are actively increasing the entropy of the world (which life goes 
> against). I don't need a god to tell me what's good and bad; for me, > 
> actively increasing entropy is bad, decreasing entropy is good - in > a 
> general sense, but often specifically too.

Also, entropy changes (positive or negative) due to human activities 
surely pale in comparison to entropy changes in the immense physical 
systems on earth -- the evaporation of all our surface water, the yearly 
formation and melting of ice, the heat exchanges that take place through 
our climate. And even here we cannot assume that entropy always 
increases, because the earth is not an isolated system as it receives 
energy from the sun, cosmic rays, asteroids, comets, starlight, etc. 
etc.

For these reasons it's never made any sense to me why entropy arguments 
prove anything about our world-at-large, even if Jeremy Rifkin did write 
a book about it. If you want to say that increasing disorder (in some 
general, human-based definition) is to be avoided in life, that's fine, 
but linking it with entropy and then attempting to pull in thermodynamic 
theorems is just simply wrong.

David