Re: question about entropy

takmais@xxxxxxxxx wrote:
> hello.. i'm a layman(how many posts start out this way?) is it fair to
> say that in a very general sense, entropy is the measure of local
> variations in the energy level of a the universe as a whole? in other
> words(yes this if more for my benefit than your's) the 2nd lay of
> thermodynamics says that the total entropy of the universe must always
> increase right? this still allows for the possibility of negative
> intropy on a local level. local level in this case means both spatial
> and temporal locality. so that in this way, the earth and all of its
> complexity including humans and our subjectivly complex lives etc
> etc... coudl all "evolve" over the past 4 billion years or so seeming
> violation of the second law, yet still not violate the second law
> because this is a spacially and temporally local phenomenon? just
> wondered if this was a fair description.. thanks
> jtg

The entropy decrease associated with evolution is small change.
Consider: Somewhere in the world it is raining. Where does the rain
come from? It condenses out of the air. A small raindrop might
contain 10^18 water molecules. By comparison, the over three billion
nucleotides in human DNA is a small number. All of these molecules
used to be randomly distributed throughout the air, but now they've all
gathered together in one place.

Could this have happened by chance? Certainly not. Raindrops grow
because there is a attractive force between water molecules that are
close to each other. But an attractive force alone won't make the
water molecules into a drop. The earth has been attracted to the sun
for billions of years, and has yet to fall in. Since attractive forces
are bound by the laws of thermodynamics, all the attractive force can
do is convert the water molecule from a state of unpredictable position
to one of unpredictable momentum. Without something else to transfer
the entropy to, the random motion of the water molecules will tear the
raindrop apart.

But fortunately, water molecules can lose their momentum by striking
slow-moving air molecules, or by emitting infrared light. Neither
process violates the second law, because in each one, the entropy does
not disappear, but is transferred to something else.

Another thing to note about both processes is that in both cases, the
water molecule loses energy. Reducing entropy is not possible without
losing energy. Thermodynamics sets a lower bound on this energy, which
is proportional to the temperature of the environment. All the second
law says about evolution is that to create something of the complexity
of the human genome at a temperature greater than the freezing point of
water, you need to use, at a bare minimum, about 1.5 * 10^11 joules.
That's less energy than it takes to lift a paramecium its full length.

And that is why people who understand physics laugh whenever someone
tries to use the second law of thermodynamics as an argument against
evolution.

.

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