Entropy and Evolution, Part 1

I was reading Dr. Hunter’s blog yesterday, and he had a post about entropy and evolution. In that post, he cited an article that comes to the right conclusion on the issue, but for the wrong reason. In fact, I am surprised that it passed peer review, since it promotes a very bad misconception regarding the Second Law of Thermodynamics. Because both creationists and evolutionists do a very poor job of applying the Second Law of Thermodynamics to the concept of origins, I thought I would try to explain the proper way to interpret the Second Law of Thermodynamics. In the next post, I will then apply the Second Law to the concept of evolution.

Before I get started, however, let me tell you the overall conclusion. The Second Law of Thermodynamics DOES NOT forbid the process of evolution. I know there are many creationists out there who claim that it does, but they are simply wrong. In addition, I know there are a lot of evolutionists out there who claim that it doesn’t, but they do so for reasons that are often wrong. So let’s talk about the Second law of Thermodynamics and how to properly apply it to many situations, including the process of evolution.

There are many ways you can state the Second Law of Thermodynamics, but for our purposes, here is an accurate description:

In any isolated system, the total entropy must always stay the same or increase. It can never decrease.

The four boldface words are very important and need to be discussed. Let’s start with “isolated system.” The Second Law of Thermodynamics, in principle, applies only to systems that exchange nothing with the outside world. Of course, such a system is rather rare in nature, because most things interact with other things. However, there are two ways you can deal with this problem.

First, you can analyze systems that are approximately isolated. For example, an incredibly well-insulated container may allow the contents inside to be virtually shut off from the world around the container. While not a perfectly isolated system, it comes fairly close, and as a result, the Second Law applies fairly well. The other way to deal with the problem is to apply the Second Law to the universe as a whole. After all, as far as we know, the universe doesn’t interact with anything outside itself, so it is probably an isolated system. I will choose to do the latter. Thus, for my purposes, the Second Law of Thermodynamics reads:

The total entropy of the universe must always stay the same or increase. It can never decrease.

Now you might think I have just made things really hard on myself. After all, the universe is a big place. Can I really deal with it effectively? Surprisingly, I can. All I have to do is split the universe into two components: the system in which I am interested and its surroundings. For example, let’s suppose I want to study some water in a bucket. I can define the water as my system, and everything else (the bucket, the air, the ground, me, etc.) as its surroundings. How does this help? Wait and see.

The other words we need to worry about are total entropy. Entropy is a measure of disorder. The more disordered a system, the higher its entropy. While disorder might be a hard term to quantify, think of it this way: The harder it is to keep track of all the components in a system, the higher that system’s entropy. So…think about a mirror that is hanging on a wall. The mirror has some amount of entropy, because it has lots of molecules that make it up, and keeping track of all those molecules can be difficult. Next, suppose the mirror falls off the wall and shatters. Now the mirror is in lots of little pieces. Because of this, it is even harder to keep track of everything that makes up the mirror, so the mirror’s entropy has increased. Thus, the broken mirror has a higher entropy than it did when it was intact and on the wall.

Now let’s go back to the original system I defined. Suppose that my bucket of water and its immediate surroundings are all at 1 degree Celsius. Then, let’s suppose the weather cools a bit, and the temperature drops to -1 degree Celsius. What will happen to the water in the bucket? Everyone knows the answer to that question: Given enough time, the water will freeze, right? That is, indeed, what happens, but when that happens, its entropy decreases.

When it is in its liquid phase, the molecules in water are free to move about. They move around, crashing into each other, crashing into the walls of the bucket, etc. As a result, they are fairly hard to keep track of. However, when water is in its solid phase, the molecules just vibrate back and forth. Thus, they are easier to keep track of, and therefore water in its liquid phase has more entropy than water in its solid phase. In fact, if you do the measurements, you will find that when water freezes at -1 degree Celsius, its entropy decreases by about 30%.

Now wait a minute. Doesn’t that violate the Second Law of Thermodynamics? The water’s entropy decreased, but the Second Law says that entropy must always stay the same or increase. Actually, the answer to this question is a definite “NO,” because we have only considered the system. We have not considered the rest of the universe. Remember, the Second Law applies only to isolated systems, so the way I am treating it here, it applies only to the universe as a whole. Thus, we have to think about what happens to the rest of the universe when the water freezes.

So what does happen? Well, when water freezes, it must release energy. Why? Remember what I told you about the molecules moving about. In its liquid phase, the molecules in the water move around quite a bit. In its solid phase, the molecules of water only vibrate. Thus, in the solid phase, water molecules have a lot less energy than they do in the liquid phase. So…to go from moving around to just vibrating, they must release energy. Where does that energy go? It goes into the water’s surroundings.

So when the water freezes, its surroundings actually heat up. What happens to a substance’s entropy when it heats up? The entropy increases. Think about it. As the bucket heats up, its molecules vibrate faster. That makes them harder to keep track of. As the air around the water heats up, the molecules in the air move more quickly, making them harder to keep track of. So…when the water freezes, its entropy decreases, but the entropy of its surroundings INCREASES. The total entropy of the universe is the sum of the entropy of the system (the water) and the entropy of its surroundings (everything else).

If you do the measurements, you will find that at exactly 0 degrees Celsius, the increase in entropy of the surroundings caused by water’s release of energy is equal to the decrease in entropy of the system cause by water’s freezing. Thus, when water freezes at 0 degrees Celsius, the entropy of the universe stays the same. When water freezes at temperatures below 0 degrees Celsius, the entropy increase in the surroundings is greater than the entropy decrease of the water, so the total entropy of the universe increases.

However, at temperatures above 0 degrees Celsius, the entropy increase of the surroundings caused by water’s release of energy would be less than the entropy decrease caused by the water freezing, so water cannot freeze at temperatures above 0 degrees Celsius. In other words, water freezes at temperatures of 0 Celsius and below because that’s when the entropy of the universe stays the same or increases. Thus, those are the only conditions under which the freezing of water obeys the Second Law of Thermodynamics.

This is why applying the Second Law of Thermodynamics can be so tricky, and it is why both evolutionists and creationists often get it wrong. In the end, the Second Law of Thermodynamics doesn’t say that no system can decrease in disorder. It says only that no isolated system can decrease in disorder. Since it is hard to construct an isolated system other than the universe, you must keep track of what the system does to its surroundings. Only then can you apply the Second Law properly. So systems can decrease in entropy, as long as there is a corresponding increase in entropy for the system’s surroundings.

That’s the “take home” message from this post. However, notice the word “corresponding” in the sentence above. That’s an important word as well, and that’s what the article I linked above (and most evolutionists) don’t understand when they apply the Second Law of Thermodynamics to evolution. I will deal with that in my next post.

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