Observer wrote:
Eandil, I suggested your magic system implies a world without entropy because in Earth's universe, and presumably many Earth-like conworlds, entropy cannot be reversed. Hawking explains it well in A Brief History of Time. I'll try here.
In short, there are infinitely more disordered states than ordered states. Imagine all the atoms in a tea cup. There is only one possible arrangement of those atoms which forms a whole tea cup, whereas there are an infinite number of arrangements which don't.
It has been demonstrated that the amount of energy waste produced in the creation of an ordered state will always be greater than the order produced. For example, if you hand-crafted a teacup (thereby creating order), your simply exuding body heat would have created quadrillions of times more disorder in the universe than the order you created by crafting the cup.
Because your magic system implies things about order and chaos, and particularly because you stipulate that either can "win," this implies that your magic system doesn't apply to a universe with entropy.
But "order winning" doesn't mean reversing entropy. It just means that sentient beings which are labeled as "good" prevent other sentient beings which are labeled as "evil" from
further advancing the universe towards a chaotic state. But this refers more to concerns about biology and sentient affairs (wars, societies, etc.). In this case, apply chaos and order to for example life. Don't think about long-term issues, just the fact that demons will want to destroy other societies, cities, wreak havoc, etc. On the contrary, good beings will try to prevent that, by continuing building cities and just their life.
It's not that ice melting is morally evil because it increases entropy, or that the purpose of angelic beings is achieving the maximum-energy state in the universe; it's more like that, when cultures meet, evil ones will seek to destroy others and good ones will be constructive. Holy magic seeks to regenerate wounds to the normal state, the ordered state of the body (which refers to biology); shadow magic tends to break it apart. Demons arose from the sea of chaos and they seek to go back to it, but the rest of beings don't share these goals.
And, most importantly, the concept of entropy applies to a closed system, but the particular universe needn't be a closed system, getting energy from somewhere else (a bigger multiverse cosmos, maybe) (also again, I was thinking of order and chaos as more in "biologically constructive/destructive" rather than physical). Does this make more sense?