(The HPMOR discussion thread after this one is here.)
This is a new thread to discuss Eliezer Yudkowsky's Harry Potter and the Methods of Rationality and anything related to it. There haven't been any chapters recently, but it looks like there are a bunch in the pipeline and the old thread is nearing 700 comments. The latest chapter as of 7th March 2012 is Ch. 77.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author's Notes.
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: one, two, three, four, five, six, seven, eight, nine.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically:
You do not need to rot13 anything about HP:MoR or the original Harry Potter series unless you are posting insider information from Eliezer Yudkowsky which is not supposed to be publicly available (which includes public statements by Eliezer that have been retracted).
If there is evidence for X in MOR and/or canon then it's fine to post about X without rot13, even if you also have heard privately from Eliezer that X is true. But you should not post that "Eliezer said X is true" unless you use rot13.
I'm puzzled by Harry's sunlight potion. Did it not require a magical ingredient?
Since we are told that there are no magical ingredients in the lesser woods where the battles are fought, and that all the potions in the books that Harry looks through unlock and redistribute magical energy (rather than ostensibly non-magical energy like sunlight), does this mean that Harry discovered a way to brew potions without magical ingredients? I recall no hint that this is possible, and yet no one watching the battle seems to find the potion notable. To be fair, the fundamental potion-making law doesn't explicitly rule out an all-mundane potion ("A potion spends that which is invested in the creation of its ingredients").
I also find it unlikely that Harry invented the potion himself (I believe general potions-theory and the system for deducing the proper arbitrary stirring patterns would have been given a more complete coverage, if that were the case), so it appears that Harry found a suitable potion using Flitwick's recommended resources. But I still don't know whether the "magical ingredient requirement" is absolute (and Harry bypassed it just by, e.g., putting something of his own magic into the potion as a trigger but not as the main ingredient), whether it's a mere conceptual limit that wizards never thought to test, or whether potions with non-magical ingredients exist and are well-known, but are relatively so rare that Harry just didn't happen to run across any in his initial search.
What am I missing?
My theory is that potions which don't involve magical ingredients are obscure because they're usually less powerful and because they require a greater investment of energy from the creator to do the reshaping (explaining why Harry doesn't do very much in that battle). Given that Flitwick and McGonagal had suggestions of books to make at all after hearing what Harry wanted, it seems very likely that such potions do exist, just not in the standard textbooks. It seems very likely that Harry got his potion out of a book, because potions research is dangerous and presumably very time consuming, and because Harry with the ability to invent potions would be powerful enough to wreck the story.