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Ok, I don’t think we disagree. But knowing that entropy is a property of a distribution given by that equation is far from “being it” as a definition of the concept of entropy in physics.

Anyway, it seems that - like many others - I just misunderstood the “little need for all the mystery” remark.



> is far from “being it” as a definition of the concept of entropy in physics.

I simply do not understand why you say this. Entropy in physics is defined using exactly the same equation. The only thing I need to add is the choice of probability distribution (i.e. the choice of ensemble).

I really do not see a better "definition of the concept of entropy in physics".

(For quantum systems one can nitpick a bit about density matrices, but in my view that is merely a technicality on how to extend probability distributions to Hilbert spaces.)


I’d say that the concept of entropy “in physics” is about (even better: starts with) the choice of a probability distribution. Without that you have just a number associated with each probability distribution - distributions without any physical meaning so those numbers won’t have any physical meaning either.

But that’s fine, I accept that you may think that it’s just a little detail.

(Quantum mechanics has no mystery either.

ih/2pi dA/dt = AH - HA

That’s it. The only thing one needs to add is a choice of operators.)


Sarcasm aside, I really do not think you are making much sense.

Obviously one first introduces the relevant probability distributions (at least the micro-canonical ensemble). But once you have those, your comment still does not offer a better way to introduce entropy other than what I wrote. What did you have in mind?

In other words, how did you think I should change this part of my course?


Right, I see what you're saying. I agree that there is a lot of subtlety in the way entropy is actually used in practice.




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