Welcome to another episode of Sciency Words, a special series here on Planet Pailly where we take a closer look at the defintions and etymologies of science or science-related terms so we can expand our scientific vocabularies together.  Today’s term is:

ENTROPY

This is not the first time I’ve written about entropy. In fact, entropy was the subject of my very first (sort of, see footnote) Sciency Words post way back in 2011.  I was still trying to figure out this science stuff back then, and I was also still trying to figure out this whole blogging thing. It’s a little embarrassing to look at that old post now, so I hope none of you will click this link to see it for yourselves.

Back in 2011, I defined entropy as disorder.  Specifically, I said:

Entropy: (noun) A measurement of the amount of disorder in a mechanical system.

This thing about disorder is a very common and rather superficial way of defining entropy.  I’ve since seen and heard the term defined in lots of different ways, some more or less appropriate depending on which scientific field you’re talking about.

My favorite definition today is:

Entropy: (noun) a measure of the amount of energy in a closed thermodynamic system that is no longer available to do work.

And according to the second law of thermodynamics, the total entropy of a closed system will always go up.  This is true whether you’re talking about a steam engine or a living organism or the entire universe.  In any closed system, entropy keeps going up.

When I wrote that original Sciency Words post on entropy back in 2011, it didn’t occur to me to look up the word’s etymology.  That’s a shame, because this turned out to be one of the easier etymologies I’ve researched. I kind of assumed entropy would have some long, convoluted history tracing back to ancient Greece.  I mean, the word looks like an ancient Greek word to me.

But no, the word entropy was coined as recently as 1865 by German physicist Rudolf Clausius, the same person who originally formulated the second law of thermodynamics.  According to Wiktionary.com, the word is formed by analogy with the word energy, which comes from two Greek root words meaning “in work” or “in the process of working.”  So entropy derived from two Greek words meaning “in transformation” or “in the process of transformation” (so at least I was on the right track thinking the word looked like Greek).

This has led me to think up yet another way to define entropy, a definition that I feel stays a little more true to that “in transformation” meaning that I suspect Clausius was going for.  Let me know what you think of it in the comments.

Entropy: (noun) the gradual but inevitable transformation of what is useful into what is useless.

Footnote: I actually wrote several blog posts before that titled Sciency Words, but those really weren’t the same, and I wouldn’t consider them part of the Sciency Words series.

### 8 responses »

1. I’ve never cared for the disorder definition of entropy. It’s always struck me as inherently value-laden, which doesn’t seem to fit in a description of nature.

That etymology is interesting because my own way of thinking of entropy is the degree to which a system has gone through its possible transformations, or how close it is to its final resting state (sans an infusion of new energy).

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• J.S. Pailly says:

Learning the etymology did sort of help crystalize what this word means in my head. I’ve had this gut feeling about what entropy is, but I could never put it into words. I knew for a long time now that it’s more complicated than mere disorder. So the transformation thing sort of cleared things up for me a little.

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2. chemistken says:

I define entropy as the source of all those nasty thermodynamic problems I had to solve in chemistry back in college.

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3. gymnosperm says:

If you look closely, all of the above definitions are value-laden. Even Boltzmann’s equation defines entropy as the number of ways the components of a microscopic system (invisible to us) can be rearranged without changing the macroscopic appearance (we can see). The value implicit here is human perception.

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• J.S. Pailly says:

You’re not wrong. Personally, I have a hard time not making a value judgement of some kind when it comes to entropy. Or at the very least, I have a hard time not feeling a little existential about it.

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4. I never truly understood this, but I recall one of my college physics professors explaining entropy that it’s better for 4 people stranded in winter to sleep in holes 2 and 2 instead of all 4 in one hole. He said all 4 together would increase entropy and they would freeze faster.

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• J.S. Pailly says:

That’s a weird one. Maybe you lose heat faster when more bodies are involved, and since that heat energy isn’t doing the work of keeping you warm anymore, entropy goes up? I don’t know. That’s very puzzling to me too.

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