Entropy & Evolution - PLEASE SHUT UP ALREADY
PZ Meyers, a new favorite of mine despite deep political disagreements with the man (he’s a dirty, dirty hippie), is kind of a lightning rod for creationist zealots, as this recent email makes abundantly clear. I must say that I love the way he quotes them in Comic Sans. In any case, the email from one Martin Patterson is pretty par for the course, but as a chemistry student I want to focus on the Second Law of Thermodynamics.
Specifically, the second law deals with Entropy, which has unfortunately come to be known as “disorder” or “chaos” in the common lexicon, but is really a measure (in physics anyway) of how unavailable a system’s energy is to do work. In chemistry we’re usually talking about the number of states that the system can take on*. I tend to think of it similarly to adding more tumblers to a lock, or making the size of your selection for permutations or combinations larger. The point is that Entropy in the universe increases over time - the universe can take on more states as a result of changes in it.
That says nothing about the Entropy change in the system in question. You can think of the Earth as a system and the rest of the cosmos as the surroundings — suddenly spontaneous evolution doesn’t seem like such a big hairy thermodynamic deal. It’s also helpful to remember that energetically speaking the Earth is not a closed system and that Entropy is not the only thing considered when looking at whether a reaction will proceed spontaneously.
The above wikipedia link contains the Gibbs Free Energy Equation, one version of it, anyway. Gibbs free energy is used to figure out if a reaction is spontaneous (that is, proceeds without you poking at it). It looks like this:
Where ΔG is the free energy, ΔH is the enthalpy change (change in heat), T is the temperature in Kelvin and ΔS is the entropy change.** Spontaneous processes release rather than absorb energy, which means that for anything spontaneous the free energy (ΔG) is less than zero. So, when determining whether or not a process will proceed on its own (irrespective of the rate at which it does so) you look to see how much heat is released or absorbed, then subtract from that the entropy times the temperature in Kelvin.
Here’s the rub, though: in most cases the entropy component of the equation is insignificant to the direction of the free energy. In organic chemistry it’s often ignored completely with chemists assuming for the sake of ease that ΔG = ΔH. Now the physical chemists will get all up on you about that, but in most organic reactions that assumption will serve you well enough. Let me repeat that: The entropy change is almost always irrelevant when determining whether or not an organic reaction will proceed spontaneously.
Organic chemistry is the basis of life - proteins, enzymes, DNA, RNA, carboxy acids, sugars, carbohydrates - these are all organic compounds and whether or not their reactions will happen without outside influence is not dependent upon entropy in any meaningful way! So, creationists, SHUT UP ABOUT THIS! I’ve taken four semesters of chemistry, that’s it, and this is a bloody obvious point. Gibbs free energy is first semester Gen Chem. Oy.
* EX - Breaking bonds increases Entropy, making bonds decreases it. That implies that larger molecules are entropically disfavored, but that’s not the only consideration.
** If the characters in front of the letters aren’t rendering correctly for you, imagine that they are capital deltas.
Tuesday, December 30 12:13 am
Actually, entropy matters a lot in biochemistry when you get to things like membrane structure and stuff. And in those cases it often (no, not always, but often) turns out that for a dense packing entropy actually favors order over disorder. The reason is that in a disordered system the components have less room to wiggle, but if everything is ordered then everything gets to carve out its own little space and it can wiggle around more. Brownian motion then keeps the ordered state stable.
So entropy does matter in many areas of biochemistry, and it’s still true that the biological structures we see are consistent with \Delta G<0
Tuesday, December 30 12:21 am
See, see what I said about physicists getting all up on you about that!
Seriously, though, that’s a good point Thoreau. And I didn’t know about the dense packing thing - but it makes perfect sense as an ordered array allows each object to take on more states.
I think it also makes sense that when you get up to big honking molecules and polymers and things like cell membranes that entropic concerns are going to matter. Big molecules, sometimes slow reactions, probably not a lot of enthalpy change (I’m guessing here, don’t know much biochem at all yet)…makes sense you’d start to worry about that.
Tuesday, December 30 12:17 pm
You know why surfactants make droplets less likely to coalesce? It isn’t really much of an energetic effect. Yes, energy is what keeps surfactant molecules at the interface between the oil and water. However, consider two oil droplets in water. If they come together, the total interfacial surface area decreases. (This is why they coalesce, because it reduces the interfacial energy.) However, if you have surfactant molecules at those interfaces, the surfactants now have less room to move around. They don’t like that. Their entropy decreases. So surfactants help keep oil drops dispersed.
Tuesday, December 30 5:03 pm
On that topic, I find it helpful to explain the concept of a system for entropy purposes and then propose the sun/earth as a system. All sorts of statistically unlikely* things can be occurring on earth (such as certain complex, energy-intensive states) simply because the sun is such a massive source of energy.
*because really, entropy is all about probability (for us physical chem people)
Saturday, January 3 10:40 am
One Handed-
very cool post!
the dood sure is a dirty hippie, as are many in the science blogs group.
One thing that’s really funny, one of the bigger H&R twaddlenocks, taran (he’s never cracked an econ book, but spews “austrian” talking points and sets himself up as a economist-homoeopath and a”skeptic”) posts regularly over there. He’s such a big, flaming pile of woo, and he pretends he’s like this big critical thinker!!
it’s totally the “apes don’t read philosophy”
“sure they do. they just don’t understand it”
:)
Sunday, January 4 11:39 am
I have a couple of pro-Creationist books I found in thrift stores, and their lack of understanding about “entropy” and other sciencey-type topics isn’t even the dumbest aspect of their philosophy. One of my books has a handy-dandy chart in the back, listing evolutionist claims and then showing which Bible verse proves these claims have to be a lie. If you told the authors “That’s an argument from authority” they would smile and say “Thank you.”
By the way, another proof of theirs that earth can’t be more than 6,000 years old is meteors: since meteors burn up in earth’s atmosphere every day, if earth were six billion yeas old then the meteorite dust would, like, be hundreds of feet thick and we’d all suffocate underneath it.
Wednesday, January 7 4:02 pm
Nicely done.
I will take exception with one implication though…
“Now the physical chemists will get all up on you…”
“See, see what I said about physicists getting all up on you about that!”
I must take exception. P-Chem is cool, and they’ve got some serious skillz. In many ways, P-Chem is like real science. But they are not physicists!
Wednesday, January 7 4:06 pm
Blindsided by the GIS attack machine!
NOBODY EXPECTS THE GIS INQUISITION!
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