The anti-evolutionists just never get tired of the second law thermodynamics! The latest bit of silliness comes from Barry Arrington, writing at Uncommon Descent. Here’s the whole post:
I hope our materialist friends will help us with this one.
As I understand their argument, entropy is not an obstacle to blind watchmaker evolution, because entropy applies absolutely only in a “closed system,” and the earth is not a closed system because it receives electromagnetic radiation from space.
Fair enough. But it seems to me that under that definition of “closed system” only the universe as a whole is a closed system, because every particular place in the universe receives energy of some kind from some other place. And if that is so, it seems the materialists have painted themselves into a corner in which they must, to remain logically consistent, assert that entropy applies everywhere but no place in particular, which is absurd.
Now this seems like an obvious objection, and if it were valid the “closed system/open system” argument would have never gained any traction to begin with. So I hope someone will clue me in as to what I am missing.
I think Arrington is missing quite a lot, actually.
Let’s start with the obvious. Many physical laws and theories only strictly apply to idealized scenarios, but that does not stop them from being very useful. There are no ideal gases in nature, but we have an ideal gas law that tells us how they behave. Physical objects never engage in perfectly elastic collisions, but classical mechanics tells us quite a lot about what would happen if they did. Heck, there are no triangles in nature, but trigonometry is still fantastically useful stuff.
So, yes, the only truly closed system is the universe as a whole, a fact pointed out in virtually every book on thermodynamics. But there are many systems that are close enough to closed for practical purposes, and that is enough to make the second law very useful indeed.
(Incidentally, for the purposes of this post I won’t belabor the distinction between a closed system and an isolated system. The former refers to one where no mass is crossing the system’s boundary, while the latter requires that neither matter nor energy is crossing the boundary. If you are making the statement, “Entropy cannot spontaneously decrease,” then you had better be talking about an isolated system. While we’re at it, for the purposes of this post I will be discussing everything in the context of classical thermodynamics. I will not discuss statistical mechanics or anything like that.)
The bigger thing that Arrington is missing, however, is that there is so much more to the second law than the statement that entropy cannot decrease in an isolated system.
One frustration in learning about thermodynamics is that you can consult a multitude of textbooks and popularizations and never find the second law stated the same way twice. Sometimes it is boiled down to the simple statement that heat always travels from a hot body to a cooler body. Sometimes it is expressed in terms of heat engines. Sometimes it is presented with an impenetrable amount of mathematics. Making things worse is that it is very hard to pin down what, precisely, entropy is. That’s why you get a lot of talk about complexity, or randomness, or useful energy, in popularizations of this topic. These ideas capture some of the spirit of the concept, but they also fool a lot of people into thinking they know what they are talking about.
When creationists first noticed that the second law could be used to rhetorical advantage, they tended to do so in a shockingly naïve way. For example, here’s Henry Morris, from his book The Troubled Waters of Evolution:
Evolutionists have fostered the strange belief that everything is involved in a process of progress, from chaotic particles billions of years ago all the way up to complex people today. The fact is, the most certain laws of science state that the real processes of nature do not make things go uphill, but downhill. Evolution is impossible!
There is … firm evidence that evolution never could take place. The law of increasing entropy is an impenetrable barrier which no evolutionary mechanism yet suggested has ever been able to overcome. Evolution and entropy are opposing and mutually exclusive concepts. If the entropy principle is really a universal law, then evolution must be impossible.
Now, when creationists are saying things like that, it is perfectly reasonable to emphasize in reply that the second law only precludes spontaneous decreases in entropy in isolated systems, which the Earth certainly is not. But that statement is hardly the entirety of what physicists know about entropy.
To fully understand the magnitude of what Arrington is missing, we should consider what the second law was accomplishes. The principles of thermodynamics make certain claims about what sorts of processes are physically possible. The first law asserts that energy must be conserved in a thermodynamical process. Energy can be inventoried, you see, and if the tally at the end differs from the tally at the start, then your hypothetical process is not possible. In practical situations, if your tallies do not match then you have probably overlooked some source of energy. It was from such reasoning that neutrinos were discovered, but that’s a different post.
The trouble is that there are many hypothetical processes that, empirically, never happen, but which are not ruled out by the first law. For example, heat is never seen to flow spontaneously from a cool body to a warmer body, but such a thing is not precluded by the first law. This is where entropy comes into it.
As I said, it’s very hard to say what, exactly, entropy is. What matters, though, is that, like energy, it can be inventoried. The second law then makes a definite statement about the manner in which entropy can change as the result of a thermodynamical process. Here is that statement:
On the left we find the change in entropy as a result of the process in question. Fully understanding the integral on the right takes some doing, but there are really only two things we need to know for the purposes of this post. The first is that this inequality applies to any sort of system: open, closed, isolated, whatever. The second is that in an isolated system the integral is quickly seen to evaluate to zero. In this special case, the second law reduces to the statement that the change in entropy in an isolated system cannot be negative, which is to say it cannot decrease.
And for an open system? In that case the integral might very well evaluate to something negative, in which case the change in entropy can be negative as well. Which is to say that in an open system the entropy can, indeed, decrease.
So it’s pretty clear that Arrington has missed rather a lot. His view of the second law is so impoverished that he has missed most of what the law actually says.
Can we save the anti-evolutionist argument by showing that evolution would violate that inequality? Good luck with that. If you figure out how to determine the entropy of an elephant, much less an entire biosphere, you will have accomplished something very impressive indeed. In practical situations, that integral can be very hard, or impossible, to evaluate. As it happens, some physicists have attempted to estimate the change in entropy on Earth as a result of evolution, bending over backwards to make extravagant assumptions that are harmful to the evolution side. Their consistent finding is that, even given those assumptions, the change in entropy is many orders of magnitude smaller than what the second law precludes. Feel free to challenge their details, but that is what you are up against if you want to revive the creationist argument from the second law.
Confronted with these basic facts about thermodynamics, anti-evolutionists respond in a number of ways. Some, like Arrington’s blogmate Granville Sewell, try mockery. Sewell likes to talk about the “illogical compensation argument” that evolutionists invoke to avoid conflicts with the second law. By this he means the idea that spontaneous decreases in entropy are possible so long as they are offset by greater increases elsewhere. Here on Planet Earth, what Sewell describes as illogical is understood simply as a straightforward consequence of what the second law says.
Others prefer something like this: “So what if sunlight is entering the system? How does that explain anything? If the parts of a 747 are lying disassembled in a junk yard, shining a light on them won’t cause them to make a functioning jet! Hahahahaha!” This is deeply silly, of course. There’s a big difference between showing that an hypothesized natural process does not violate the second law, and showing that it is reasonable to believe that it happened. Consistency with the second law is a very low hurdle. In principle there might be all sorts of reasons for challenging theories of evolution or the origin of life. The point for now, though, is that those reasons will not have anything to do with the second law.
The reason anti-evolutionists seem so impervious to the elementary points I have made here is that, for all their blather about the second law and entropy and whatnot, their arguments generally have nothing to do with thermodynamics. They almost never employ any of the machinery that you see laid out in the textbooks. They are really just saying that they find it hard to believe that evolution can cause complexity to increase. The thermo-jargon is just a way to make the argument from personal incredulity sound scientific. So, when a scientist explains the facts of thermodynamical life to him, the anti-evolutionist does not hear a reply to the argument he is really making. And that is why he will usually retort with a non sequitur.
Anti-evolutionists really need to stop talking about thermodynamics. Every time they do they just show the world why scientists are so contemptuous of them.