Timeline for Is it possible for the entropy in an isolated system to decrease?
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| Oct 6, 2013 at 21:42 | comment | added | user4552 | @eJunior: Sure, in that trivial sense it's arbitrary. It's arbitrary up to a multiplicative constant, and the constant can be negative if you switch the words around in the 2nd law. | |
| Oct 6, 2013 at 21:22 | comment | added | eJunior | Or do you mean that we could arbitrarily change the definition of entropy from lnΩ to −lnΩ, in which case it would always decrease? I meant exactly that. If it has a 'sign' and it cannot go the opposite way what is it's 'mathemathical value'. | |
| Oct 6, 2013 at 19:40 | comment | added | user4552 | @eJunior: Sorry, I don't understand your comment. Did you write "decreasing" and "increases" when you meant "increasing" and "never decreases?" Or do you mean that we could arbitrarily change the definition of entropy from $\ln\Omega$ to $-\ln\Omega$, in which case it would always decrease? In essence it only means one state goes towards another and dont ever go back to its previous state (in isolation). This is sort of true, see Lieb and Yngvason, arxiv.org/abs/math-ph/0003028 . But that doesn't mean that the definition of entropy is arbitrary. In fact, L&Y prove that it's unique. | |
| Oct 6, 2013 at 18:31 | comment | added | eJunior | I think he means arbitrary in the sense that 'increase' or 'decrease' are arbitrary definitions. You could say: (1) entropy is always decreasing; and (2) entropy never increases. In essence it only means one state goes towards another and dont ever go back to its previous state (in isolation). | |
| Oct 6, 2013 at 18:18 | history | answered | user4552 | CC BY-SA 3.0 |