Doesn’t the Second Law of Thermodynamics say that evolution can’t take place?
This subject is a bit more technical than the others that I use on the BLOG. But I think that is important to discuss because this may be the single, most frequently used argument against evolution.
Thermodynamics is a part of physics. It is the study of energy, particularly heat energy. There are three scientific “laws” associated with thermodynamics. (While not an expert in this subject, I am not a novice. I took a course in thermodynamics in college as I worked on my engineering degree.)
The Second Law of Thermodynamics (sometimes simply called “the Second Law”) states:
The total entropy of any isolated thermodynamic system tends to increase over time, approaching a maximum value.
You’re probably asking yourself these two questions right now:
1. What the heck does that even mean? What is "entropy"?
2. How does that apply to evolution?
Those are both good questions.
First we need to understand what entropy is. The Second Law of Thermodynamics is little more than a definition of entropy.
Entropy, in most senses, is a measure of the disorder of a system. (We’ll come back to this.)
While it is used in fields of study such as information theory it is probably easiest to understand in thermodynamics (believe it or not). In thermodynamics, entropy is the “useful” energy in a system. In other words it is the amount of energy that can be put to work. The most common example of energy doing “work” is energy used to make a piston move.
To oversimplify a bit, in order to make energy do work you need temperature differences. When everything is the same temperature, energy can’t do any work.
In a classic example, ice melting in a glass is approaching room temperature and the work that can take place due to “useful” energy diminishes.
That is what entropy is.
That has nothing to do with evolution.
But the word “disorder” fascinates creationists. They use that to argue against evolution.
Indeed our own intuition tells us that disorder is always increasing everywhere. The amount of disorder only diminishes when intelligent intervention takes place.
Things break down. That means that the amount of disorder has increased. When things break, we get them fixed. Some intelligent being, such as an automobile mechanic, gets in there and works to fix it.
This is where the Second Law of Thermodynamics finds its relevance to evolution. It is in the aspect of “disorder”. Evolution says that things are not always becoming more disordered. Human beings are more ordered (less disordered) than the single cell organisms that are, hypothetically, the first living things.
So doesn’t evolution violate the Second Law of Thermodynamics?
No! Decidedly not!
Disorder is a statistical thing. While all of us have a sense that the amount of disorder is always increasing, we also know of examples where – at least in small areas – it decreases.
One example comes from shuffling a deck of cards. The entire purpose of shuffling the cards is increasing the amount of disorder (i.e. make the sequence of the cards as random as possible).
Yet, if you take a well-shuffled deck of cards and examine it, you find sections that are ordered rather than disordered. Maybe you’ll see three kings in a row. Or you might see the 7-8-9-10 of diamonds in sequence. You’ll almost always see something that looks ordered even in a very disordered deck of cards.
The disorder of the deck in total is increased because the total sequence is more random. But here and there you will see examples of more order.
No one who understands the Second Law would disagree with this.
What that means is that the truly random parts of evolution – mutations – don’t violate the Second Law. Most mutations are neutral or negative, but the occasional positive mutation is effectively no different from finding a four card sequence in a well shuffled deck of cards. It can happen completely at random. It doesn’t violate the Second Law.
Furthermore, ss we all know, evolution has a process that sorts the beneficial mutations (i.e. those with increased order) from those that are more disordered. That process is called natural selection. It is, as the name implies, a natural process.
In fact, natural processes other than natural selection can sort random things. For example, waves hitting a beach will sort rocks by weight. The lighter rocks will be closer to shore. The heavier rocks will be further away from shore. That is a process that increases order. No law of thermodynamics is violated by those waves. (Surely anyone who has watched the action of the waves at a beach would say that any physical law is being violated.)
So the two things that cause evolution don’t contradict the Second Law. Mutations that increase order, as long as they are part of a larger group of mutations that don’t all increase order, do not violate the Second Law. The sorting process of natural selection does not violate the Second Law either.
So the Second Law of Thermodynamics is not violated by evolution.