On Entropy

I had a plugged up sink in my bathroom the other day. It happens: my pipes are old and I have kids. What I’ve been told by people that know more about it than I do is that as we wash our hands and stuff, the dirt and grime accumulates in the pipes, and eventually this closes up, then the water moves more slowly. So slowly that it takes all night to drain the sink from full.

But I grew up on thirty acres of forest. I’ve seen how creeks work in the wild. Water runs down the creek and pulls dirt and grime away. The creek does this so efficiently that it will even widen out. The creek carries dirt away. The pipe fills up with dirt. But the process is the same: water passing through.

There is a principle in physics called The Third Law of Thermodynamics. The idea is that as time goes on, the certainty of the start state becomes lower and lower. The lower certainly about how near a state is to the beginning is called an increase in entropy. Often, this is described in terms of disorder increasing. “Disorder” is a word that will cause some physicists to cringe, though. Some high entropy states feel to our senses to be very ordered.

If we start with sand in a box being blown around by the wind, we can tell that the state is very near the set-up state if all of the sand is in the corners. If the sand is fairly evenly distributed along the box, it’s less clear if that’s how the box was made or if it got there after a bunch of wind blowing the sand around. So the sand spread evenly is the higher entropy state. But there’s a sense in which the sand being spread even feels more ordered. So we can’t really rely on our understanding of what feels ordered for this.

But as I sat under my house, stabbing a plumber’s snake up the pipe, trying to dislodge a plug, it occurred to me that a pipe doesn’t really obey this principle. It obeys the feeling of the idea. I can absolutely get behind the idea that the plug represents disorder. These pipes are meant to flow water away from my sink. That they fail to do this is disordered. But I actually have a very good idea how far along the process it is. It’s at the end of the process.

In order for entropy to apply, what I would really expect is for the dirt and grime to reach a point of equilibrium. Maybe not exactly half-way full, but functionally half-way full. A place where dirt and grime are carried away and deposited at the same rate. As the pipe plugs, pressure should go up a little, and it should draw more away.

I also realized that this isn’t the only thing in life that works this way. As our bodies age, forensic biologists actually have very little difficulty picking a random organ and estimating the age of the individual. Of course, some are more reliable than others, but if you give them ten hearts the chances are high that they’ll estimate the age within about 2% on seven of them.

Now, I’m not really suggesting that these are instances where the Third Law of Thermodynamics is broken. There’s more nuance to the Laws of Thermodynamics than just that. Someone with more practice calculating entropy could probably explain the reason that filling up the pipes is really an increase in entropy. But here’s the thing: if it worked more the way that feels intuitive to me (that the pipes fill halfway and then lose as much as they gain) then those that run the calculations would find a way to make that work, too. In that world, it would feel more consistent, though.

Even when a more consistent application of entropy would seem to imply something more convenient than our real world, the world chooses the least convenient interpretation to be reality.

Actually “least convenient” isn’t quite right. There are a lot of ways that entropy could be much harsher. But the way entropy works is the way that requires morality. If my pipes had filled part way up and then stopped, then I wouldn’t have needed to give up two weekends climbing under the house, tearing apart pipes, and running metal through the remnants to restore function to our bathroom sink.

It’s the same thing with a towel. If you dry off and leave a wet towel on the ground, it will get moldy. If you hang it up stretched out, then it will dry and be mostly fresh again in a few hours. Putting effort into planning a project has long been known to reduce the overall cost of the project. At every turn, giving more of ourselves to something early always makes it better. And this law is more consistent than even the Laws of Thermodynamics.