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It took me 10 years to understand entropy

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Re: It took me 10 years to understand entropy

#31

Post by ravi-delia »

javajosh wrote: post #23
jleyank wrote: post #7

Earlier quoted context omitted.

Nah, Ultraviolet Catastrophe is worse, then there's wavefunction collapse. And there's gotta be something in particle physics that puts these terms to shame. Given that the particle names are drawn from literature and whimsy. I looked up the dictionary definition of pretentious, and so it doesn't really apply, but the hERG channel is a critical ion channel and various drugs block this and cause Really Bad Things. hER…

"Ultraviolet Catastrophe"'s problem is that it sounds way cooler than it is. I mean, that's the title of a cyberpunk novel; more hyperbolic (and disappointing) than pretentious. Eigenthings would be second on my list of pretentiousness (oddly, not gedankenthings; I'm inconsistent I guess). Standard Model names strike me whimsical to the point of being undignified.

I'm still mad about top and bottom when truth and beauty were right there!

Re: It took me 10 years to understand entropy

#32

Post by ravi-delia »

shannifin wrote: post #14

> "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 n…

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.

Re: It took me 10 years to understand entropy

#33

Post by Hermel »

evouga wrote: post #25

One aspect of entropy that I always find counterintuitive is that unlike mass, charge, etc. it is not a physical quantity. In fact, from the point of view of an experimenter with perfect information about a physical system, the entropy of the system is exactly conserved over time (as made precise by Liouville's Theorem). The Second Law survives in this setting only in the most trivial sense that a constant function d…

Not really. Even from a point of view of an experimenter with perfect information, the entropy of the system declines over time as fewer and fewer bits are needed to describe the system.

For example, start with a Glas of warm water and an ice cube in it. Over time, the ice will melt and the range of different temperatures of the molecules decline. Consequently, you need fewer and fewer bits to describe the complete state of the system. It takes fewer Bits to encode all the velocities of a million molecules that all move at a similar speed than to encode all the velocities of a million molecules that move at very different speeds.

The more similar the state of the molecules becomes, the shorter a text becomes that has to describe the complete state of a system. Therefore, entropy is decreasing even from the point of view of an observer with perfect information.

Re: It took me 10 years to understand entropy

#34

Post by ravi-delia »

SnowHill9902 wrote: post #13

Statistical mechanics is one way of representing entropy but you don’t need it. The second law of thermodynamics can be expressed in other much more general terms. Also it requires that the system be isolated not “thermally isolated”. There’s other types of interactions such as gravitational and electromagnetic.

I mean, come on. You know and I know that the statistical mechanics definition gets you 99% of the way there in terms of intuition. Obviously if I spin a rotor in my thermally insulated box with a magnet on the outside I can add energy to order things with, I don't think anyone is confused on that point.

Re: It took me 10 years to understand entropy

#35

Post by sjg007 »

I view entropy as a probability distribution of some set of configurations of something. Entropy is low if there’s only one configuration and high if uniformly distributed.

There’s also some observer/interaction effect which is like introduction a conditional probability which would cause crystallization in an otherwise homogeneous system. Essentially a catalyst.

I also find it fascinating that when it is super cold outside and you throw a pan of boiling water out the window it turns to snow instantly vs a cup of room temperature water which does not. It probably fits in terms of activation energy as well.

Re: It took me 10 years to understand entropy

#36

Post by antognini »

jleyank wrote: post #7
javajosh wrote: post #2

Nice writeup! BTW statistical thermodynamics has a name for that set of possible microstates, perhaps the most pretentious sounding name in all of physics, the "canonical ensemble".

Nah, Ultraviolet Catastrophe is worse, then there's wavefunction collapse. And there's gotta be something in particle physics that puts these terms to shame. Given that the particle names are drawn from literature and whimsy. I looked up the dictionary definition of pretentious, and so it doesn't really apply, but the hERG channel is a critical ion channel and various drugs block this and cause Really Bad Things. hER…

My favorite is "gravothermal catastrophe" with "violent relaxation" being a close runner-up.

Re: It took me 10 years to understand entropy

#37

Post by XorNot »

raven105x wrote: post #15

Entropy: "to describe energy loss in irreversible processes". We have no clue about what is or is not reversible. Complex systems exhibit self-organizing behavior for no reason (that we understand), and we continue to identify more conditions under which this occurs. How does a Nobel Prize get handed out for identifying/quantifying "self-organization" http://pespmc1.vub.ac.be/COMPNATS.html without bringing everything…

> Self-organization does not consume energy any more than entropic decay emits it.

This statement is incredibly wrong - this is exactly what both these processes do. We calculate chemistry reaction kinetics by including entropy terms, and optimize reactions by manipulating the entropy on one side of the equation (a classic is getting a liquid phase to precipitate out as you produce it).

I mean the reason coal can be turned into electricity is because there's a big increase in entropy going from "solid carbon in a specific location" to "CO2 diffused everywhere".

Re: It took me 10 years to understand entropy

#38

Post by XorNot »

jleyank wrote: post #7
javajosh wrote: post #2

Nice writeup! BTW statistical thermodynamics has a name for that set of possible microstates, perhaps the most pretentious sounding name in all of physics, the "canonical ensemble".

Nah, Ultraviolet Catastrophe is worse, then there's wavefunction collapse. And there's gotta be something in particle physics that puts these terms to shame. Given that the particle names are drawn from literature and whimsy. I looked up the dictionary definition of pretentious, and so it doesn't really apply, but the hERG channel is a critical ion channel and various drugs block this and cause Really Bad Things. hER…

There's actually a sort of general principle in medical science that people should avoid whimsical names for things, since in all likelihood someone with a life-altering or fatal condition or their family shouldn't be told that it's due to a mutation in the Sonic Hedgehog protein [1]

[1] https://en.wikipedia.org/wiki/Sonic_hedgehog

Re: It took me 10 years to understand entropy

#39

Post by XorNot »

andrewflnr wrote: post #18
hackernewds wrote: post #16

Earlier quoted context omitted.

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.

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