Monday, September 20, 2010

Evolution and the 2nd Law

A common Creationist argument is to say that evolution by natural selection violates the Second Law of thermodynamics.  The Second Law of thermodynamics says that entropy increases over time.  Entropy is a quantitative measure of disorder.  So Creationists point to the complexity and order of life and say, "How is that consistent with natural law?"

There are any number of responses to this question, first beginning with the fact that Earth is not a closed system.  That is, the Earth has contact with a very large source of energy, the sun.  The Second Law only says that the total system (that is, the sun and the earth) will increase in entropy.  It's entirely possible for part of the system to decrease in entropy if it's offset by a larger increase in entropy elsewhere.

Creationists sometimes respond by saying, "Even if it's possible, is it really plausible?"  Absolutely!  Whenever energy gets transferred from a high temperature object to a low temperature object, this causes an increase in entropy.  So whenever the sun radiates energy onto the earth, entropy increases.  The sun radiates a lot of energy.  Transferring energy from hot to cold objects is how most processes do work (that is, they provide free energy with no entropy attached).  Engines work this way, for instance.

If you look at the total power from the sun, it turns out that one year's worth of power provides enough work to rearrange all the molecules in the Earth's biomass from a completely disordered state to a completely ordered state.  Given the long time that the sun has been powering the Earth, and given that all the molecules biomass are not even close to being completely ordered, evolution doesn't seem at all unreasonable.

Another response is that entropy is not exactly the same thing as disorder.  "Entropy is disorder" may be helpful when you first encounter the concept, but entropy is more precise than that.  Entropy is a measure of the number of different ways a system could be, and yet still look the same from the big picture.  When we look at the sun, we can tell certain things about it, like its temperature, size, and mass.  But the thing is, the sun is composed of 1057 particles or so, and they're all moving very fast in an unknown direction.  There are a whole lot of ways those 1057 particles could be configured, and yet the Sun would still appear the same temperature, size, and mass. So the sun has a huge amount of entropy.

I bring up this very large number of 1057 particles to convey the fact that disorder on the atomic scale is far more important to entropy than disorder on a macroscopic scale. Consider cars.  Our car system is highly ordered.  All the cars need to be in the exact right places so that they obey traffic laws, don't crash, and can take their passengers exactly where they want to go.  There are about 800 million cars the world.  But how many molecules are there in a single gallon of gasoline?  Somewhere around 1023, 14 orders of magnitude larger.

And now consider DNA.  Human DNA has about 200 million base pairs, each of which has only four possibilities: A, C, G, or T.  The amount of entropy involved in having the right letters is trivial compared to the entropy involved in a simple chemical reaction, like the combustion of gasoline.  It's nothing compared to the entropy involved in the radiation from the sun.

A third response is that the Creationist argument has a very limited view of what is possible within the confines of the Second Law.  To see examples of processes that are consistent with the Second Law, look around you.  Everything you see was created by the Second Law.

The Second Law is why things fall down and stay down.  It's why evaporated water goes up into the sky and forms clouds.  It's why ice cream gets warm and melts when you leave it out.  It's why freezers can be so much colder than their surroundings.  It's why when you break a clay bowl, it stays broken.  It's why, when you smoosh two pieces of wet clay together, they become one.  It's why mountains erode into nothingness, but also why mountains form in the first place.

The point is that even if the Second Law favors one result under certain conditions, it can reverse the result under other conditions.  Creatures tend to die and decay, but under other conditions, they get born.  Sure, evolution involves some reduction in entropy (however trivial compared to the entropy of a typical chemical reaction).  But every step of the way, organisms are dying and decaying.  Every step of the way, organisms are consuming food, leaving more disordered waste products.  These waste products ultimately get converted back to food with the help of photosynthesis (remember the sun?).

The process of evolution leaves plenty of disorder to go around.

I was curious, so I checked to see if this argument was on Answers in Genesis' list of "Arguments we don't use".  It is not.