liquid

As an engineering student, specialising in aerospace and all the accompanying thermodynamics, it is the area that gets me the most annoyed when I see it abused by creationists.

This often takes the form of long wordy arguments involving 'disorder', 'systems', vague allusions to the proper statement of the law and its various corollaries. Basically, it's putting the argument across in laymans' terms, because many of these people only have a rough idea of the concept.

Very often it is refuted, perfectly well, but in a similar manner. This always upsets me, because it can be done with one simple 'calculation'. But you would be amazed at the number of times this is not accepted or understood.

The change in entropy of a body can be stated as

dS = dQ/T

As living creatures metabolise;

dS = -dQ/t

=> dS is -ve

The second law quite clearly allows entropy decrease within biological systems.

[Edit: I realise this is possibly rehashing for a lot of you, but I just wanted to get it off my chest.]

[ January 22, 2002: Message edited by: liquid ]</p>

Ernest Sparks

'dS = dQ/T' is true for infinitesmally slow, reversible changes (ideal ones). For all other (more realistic) cases, it is 'dS &gt; dQ/T' that is true.

What means '-ve'??

CORRECTION: I should have said 'infinitely slow'!

[ January 23, 2002: Message edited by: Ernest Sparks ]</p>

Ernest Sparks

I would recommend a search of the careers and writings of three fine physical scientists from Great Britain, all very much gentlemen, honest researchers, and more-or-less faithful christians (Eddington was a Quaker and ,therefore, the most non-conformist of the three).

Through their works, which include some excellent and influential books for the general public, they extolled the primacy and transcendent character of thermodynamic laws, especially in regard to the ancient physical history and future physical prospects of the universe. One of them said something like "All other physical laws may pass away, but the laws of energy and entropy will not pass away." They were all quite capable of being dead wrong about things, and proved it from time to time.

<a href="http://www-groups.dcs.st-andrews.ac.uk/~history/Mathematicians/Thomson.html" target="_blank">http://www-groups.dcs.st-andrews.ac.uk/~history/Mathematicians/Thomson.html</a>
William Thomson (Lord Baron Kelvin of Largs) 1824-1907

<a href="http://www-groups.dcs.st-andrews.ac.uk/~history/Mathematicians/Jeans.html" target="_blank">http://www-groups.dcs.st-andrews.ac.uk/~history/Mathematicians/Jeans.html</a>
Sir James Hopwood Jeans 1877-1946

<a href="http://www-groups.dcs.st-andrews.ac.uk/~history/Mathematicians/Eddington.html" target="_blank">http://www-groups.dcs.st-andrews.ac.uk/~history/Mathematicians/Eddington.html</a>
Sir Arthur Stanley Eddington 1882-1944

Dr Rick

dS is the change in entropy, Q is heat and T is absolute temperature.

What are "t" (should it be "T"?) and "ve"?

[ January 22, 2002: Message edited by: rbochnermd ]</p>

liquid

t should be T in the second equation. Damn the shift button!

And dS=dQ/T is the limiting case, so its perfectly valid for the point I am trying to make, which is simply that heat emission allows for entropy decrease, and that is precisely what an evolving system does.

and -ve means negative. +ve means positive. Never seen that before?

[ January 23, 2002: Message edited by: liquid ]</p>

Oolon Colluphid

Well it all looks nice, and I'm delighted it can be (apparently) shown so simply. But I fear I'll be sticking to words...

I also fear that, great though that is, it's of little use against the garden-variety creationist, for the same reason.

Cheers, Oolon the mathematically challenged.

Oolon Colluphid

Ahh.. getting there... the d confused me... it's delta, yeah? Gotcha.

But...

Why? Erm, "change in entropy = negative change in heat over absolute temperature", right? Why's that? Sorry, you'll have to use words .

Actually, don't tell me, I'll get old textbook out and go through glycolysis and the Krebs cycle again

Oolon

Ernest Sparks

It is damned hard to get straight exposition (opposite of horrendous BLAB and misdirection) on the entropy concept. Here are the best ones I pulled in a short time:

nice and short, and sadly incomplete! -&gt;
<a href="http://physics.about.com/library/dict/bldefentropy.htm" target="_blank">basic entropy definition</a>

parts of a college physical chemistry course - thorough! -&gt;
<a href="http://www.colby.edu/chemistry/PChem/notes/Carnot.pdf" target="_blank">carnot engine</a>

<a href="http://www.colby.edu/chemistry/PChem/notes/Entropy.pdf" target="_blank">thermodynamic definition of entropy</a>

includes irreversible process case, and generally what to do with it! -&gt;
<a href="http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/ThermLaw2/Entropy/Entropy.html" target="_blank">entropy for reversible and irreversible processes</a>

It is commonplace to state that entropy is misunderstood. ISTM, Most just turn around and make sure it REMAINS misunderstood.

pooh!
Ernie

P.S. If the numerical sign of heat is switched from INPUT +ve to OUTPUT +ve, then something like dS=-dQ/T makes sense.

P.P.S. Thanks for explaining +ve and -ve to me. I HAVE seen it before and I was baffled at the time. It looked to me like some kind of electrodynamic thing.
Thanks again!

[ January 23, 2002: Message edited by: Ernest Sparks ]</p>

faded_Glory

This was recently mentioned in another thread, but see <a href="http://www.arn.org/ubb/Forum1/HTML/001520.html" target="_blank">here</a> for a thoroughly confusing creationist argument about evolution and entropy. The guy Jeptha needs more words than the bible to get his point across, and moreover he is altogether wrong.

liquid, maybe you can try to shut him up with you nice little formula ?

fG

liquid

"P.S. If the numerical sign of heat is switched from INPUT +ve to OUTPUT +ve, then something like dS=-dQ/T makes sense."

Doesn't really matter - it is just a convention and the formula changes when the sign convention changes.