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Comment by shannifin | Hacker News Reader

> "Entropy is not Disorder One of the most popular belief about entropy is that it represents disorder."

This is what confused me the most about entropy in high school, the "order / disorder" lingo. Isn't "order" a metaphysical concept, something a conscious entity thinks about a system? How would nature know the difference? It took me some years to understand that that lingo is indeed misleading. (Still definitely not an expert of course.)

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It's order in the different things in different places sense. Not the best term, since if I had to give an informational definition of order I'd probably set it up backwards, but not terrible. I like "separate" to communicate low entropy and "mixed" for high entropy, but that's just what particular examples of low and high entropy look like.

> Isn't "order" a metaphysical concept

Yes. The most scientific way of talking about "order" in that sense is the Kolmogorov complexity, which is still extremely poorly-defined. The best way to put it is that "ordered" states are ones that have low Kolmogorov complexity.

What is a way to articulate it then?

OP is about as good as any explanation I've seen.

"Compressibility" (in the software sense) would perhaps carry the most meaning.

Entropy is ultimately all about the ability to extract information (i.e. work) out of a system.

Indeed, it was actually James Gleick's book The Information that helped me understand the concept better.

"Compressibility" is really not that great an illustration for physical entropy. Information-theoretic entropy is not quite the same thing as physical entropy, but close enough to confuse you if you're not paying attention.

I'm going to need an example on the differences, because in so far as statistical entropy is entropy - it's ultimately describing an information function (and the lean in quantum mechanics these days is that information is describing physical properties as well - hence holography and the blackhole information paradox).

The heat-deathed universe for example would be the ultimate compressible information: 1 measurable state, across all space, for the rest of infinite time.

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