By Ken Stuckas
Aha! I knew that presumptuous message title
would catch someone! I have become increasingly
annoyed at suggestions by the Institute for
Creation Research (ICR) that Evolution violates
the second law of thermodynamics. So, I hereby
offer this monograph on the subject of the second
law and entropy. And I then offer a challenge
to anyone who is willing to use the substance
of this piece to demonstrate how Evolution could
possibly violate the second law. My qualifications?
I have a degree in aeronautical and astronautical
engineering and am a registered professional
engineer.
There are several ways to express the second
law of thermodynamics. Here are two:
- Kelvin-Planck: No "cyclic process"
is possible whose result is the flow of
heat from a single heat reservoir and the
performance of an equivalent amount of work
on a work reservoir. Energy interchanges
can take place in any direction between
any pair of work reservoirs, but energy
exchange between a work reservoir and a
single heat reservoir, "with no outstanding
changes in other systems, can proceed in
one direction only -- that in which the
work reservoir does work and the heat reservoir
absorbs heat.
- Clausius: No "cyclic process"
is possible whose result is the flow of
heat from a heat reservoir at one temperature
and the flow of an equal quantity of heat
into a second reservoir at a higher temperature.
It is, however, possible to carry out a
"non-cyclic" process in which
there is a flow of heat out of a heat reservoir
at a lower temperature and a flow of an
equal quantity of heat into a reservoir
at a higher temperature.
Temperature is a measure of heat added or rejected
for any substance undergoing a process at constant
pressure or constant volume as long as the values
of the factors of proportionality for the substance
are known. These values are called the "specific
heat at constant pressure" and the "specific
heat at constant volume." It would be convenient
to have a factor of proportionality with which
temperature could be used to measure the heated
added or rejected for "any" process,
not just processes at constant pressure and
volume. As luck would have it, such a property
exists. It is called "entropy".
Mathematically, T ds = dq, where T is the temperature
of a substance, ds, is the change in entropy
and, dq, is the incremental corresponding incremental
change in heat.
Besides the Kelvin-Planck and Clausius statements,
the second law may also be expressed in terms
of entropy. Entropy: In a real "closed"
system, total entropy can never decrease. It
is important to note the restriction that the
system must be closed -- that is, neither energy
nor mass may cross the boundaries of the system.
In other words, all elements initially in the
system must be present and accounted for in
the final reckoning. The entropy in parts of
a closed system may decrease, but that decrease
will be more than offset by an increase in other
parts of the closed system.
Let's look at a couple of semi-real examples.
(Truly isolated systems do not exist.) I have
a swimming pool divided into two halves by a
thin dividing wall. Into one half I pour ink
and into the other I pour water. I remove the
divider and wait. The ink gradually mixes with
the water (ignoring natural convection) and
eventually I have a fairly uniform mixture.
The entropy of the pool contents has spontaneously
increased through the process of molecular motion.
I can reverse the process only by introducing
into it Ken's magical ink-water separator. Using
energy I have brought into the formerly closed
system, I put the dividing wall back into place
and grab all the ink molecules and put them
in one side while at the same time moving all
the water molecules to the other side. This
could take a while. I have restored the swimming
pool to its original condition, but only by
breaking into the closed system using energy
I took from another closed system (one which
I constructed around the pool before my original
experiment began). Ken's magical ink-water separator
runs off of batteries which are now depleted
so the entropy of the second closed system has
increased as well. I could recharge the batteries,
but I would have to go outside the second closed
system and get an extension cord -- well, you
get the idea.
Here's a different example: I have a closed
system, a box of air, through which neither
energy nor mass may be transferred. In the center
of the box I have one ice cube. The air is at
70 F and the ice cube is at 20 F. I return to
the box some time later and notice a puddle
of water where the ice cube used to be. The
ice cube has spontaneously gone from a state
of lower energy to a state of higher energy
while the entropy of the ice cube itself has
increased (water molecules move about at random,
but are prevented from migrating in their solid
state). The entropy of the surrounding air which
has decreased in temperature has decreased (the
pressure in the box has decreased due to decreased
molecular motion of the air). The entropy of
the entire contents of the box has remained
unchanged.
Now that we have a better scientific understanding
of what entropy is all about we can talk further
about the misuse of the concept in areas other
than thermodynamics. The concept of entropy,
that is, the concept that things spontaneously
move toward randomness and disorder has been
captured and used as a metaphor in areas other
than thermodynamics. These metaphorical applications
of entropy are useful up to a point. They have
been applied to social dynamics and information
theory, but herein lies the rub. Metaphor has
it's limitations. We learn about new things
through simile and metaphor. But unthinking
extrapolation of a metaphor often fails.
If I ask you what a UFO looks like, having never
seen one myself, you might say, "It's just
like an upside-down dinner plate that zooms
through the air -- sort of a "flying saucer."
You have just used metaphor to explain something
to me that I have no acquaintance with. So far,
so good. Carrying the metaphor too far, I imagine
in my mind that a UFO is also made of plastic
and has little daisies around the edges just
like the dinner plates I have at home. See the
problem? Metaphor has its limits. The generalization
that "everything tends toward disorder"
when carried away from the subject of thermodynamics
can easily lead to false impressions and error.
Notice that in the Kelvin-Planck and Clausius
expressions of the second law, I used some terms
that have very specific meanings which may be
easily misunderstood by those not familiar with
the esoteric language of thermodynamics. One
must have a thorough understanding of the definitions
of heat reservoir and work reservoir. As in
mathematics, precision of definition is demanded
to avoid obfuscation.
The Challenge: I hereby challenge anyone to
use the strict definitions of the second law
of thermodynamics to demonstrate that the fact
of evolution in any way violates the second
law.
This is called science. Put up or shut up.
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dr2 | Subject: | 2002-06-08 15:41:58 |
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My thanks to Ken for this article
-
Jim
