When I was in my first or second year of college, a friend of mine who belonged to a fundamentalist Christian church in Sri Lanka said that he had heard of a convincing scientific proof against the theory of evolution. He said the proof centered on the concept of entropy. I had already heard of the term entropy at that time, but I definitely did not understand the concept, since I had not as yet studied thermodynamics in any detail.

Anyway, my friend told me that there was this law of physics that said that the total entropy of a system had to always increase. He also said that the entropy of a system was inversely related to the amount of the order and complexity in the system, so that the greater the order, the lower the entropy. Since I did not have any reason (or desire) to challenge my friend, I accepted those premises.

Then came the killer conclusion. Since it was manifestly clear that the theory of evolution implied increasing order (under the theory, biological systems were becoming more diversified, complex, and organized from their highly disordered primeval soup beginnings) this implied that the entropy of the Earth must be decreasing. This violated the law of increasing entropy. Hence evolution must be false.

It was a pretty good argument, I thought at that time. But in a year or two, as I learned more about entropy, that argument fell apart. The catch is that the law of increasing entropy (also known as the second law of thermodynamics) applies to closed, isolated systems only, i.e., systems that have no interaction with any other system. The only really isolated system we have is the entire universe and the law is believed to apply strictly to it.

For any other system, we have to make sure that it is isolated (at least to a good approximation) before we apply the law to it, and this is where my friend’s argument breaks down. The Earth is definitely not a closed system. It continuously absorbs and radiates energy. It especially gains energy from the Sun and radiates energy into empty space and it is this exchange of energy that is the engine of biological growth.

So nothing can be inferred from the entropy of the Earth alone. You have to consider the entire system of the Sun, the Earth, and the rest of the universe, and you find that this leads to a net increase of the entire closed system. So the second law of thermodynamics is not violated.

You can have decreased entropy in a part of a system provided the entropy increases by more than that amount in another part. As an analogy, consider a sock drawer in which you have black and brown socks randomly mixed together. This is a state of low order and hence high entropy. If I now sort the socks so that all the black socks are on one side of the drawer and all the brown on the other side, then the sock drawer has gone from a lower to a higher state of order, and hence from higher to a lower state of entropy. Is this a violation of the second law? No, because it ignores the fact that I was part of the system. I had to use up energy to sort the socks, and in that process my entropy increased more than the decrease in entropy of the sock drawer, so that there was a net increase in entropy of the combined system (sock drawer + me). Strictly speaking, I was also in contact with the rest of the room since I was absorbing and radiating energy, breathing, etc., so if you wanted to get to an even better approximation to a closed system to be even more accurate, you had to take the entropy of the room into account as well.

This is why physicists believe that after the Sun eventually burns up all its nuclear fuel and ceases to exist, the Earth will inevitably fall into disorder, assuming that we haven’t destroyed the planet ourselves by then. (As an aside, Robert T Pennock in his book Tower of Babel says that some creationists believe that God created the second law, with its increasing disorder, as part of his punishment for Adam and Eve’s fall from grace.)

Once I understood better what entropy was all about, that was the end of the entropy argument against evolution, at least as far as I was concerned. Non-physicist scientists generally caught on to the fact that people were using the entropy argument fraudulently against evolution and were able to debunk it whenever it came up, so that nowadays one rarely hears that argument. One still occasionally comes across the entropy argument used in this fallacious manner, however, and it may still have power over the scientifically naive.

But even if the entropy argument itself has largely disappeared, other ‘scientific proofs’ against evolution and for the existence of god have arisen in the wake of so-called intelligent design (ID) and I will look at those arguments in future postings.