If quantum mechanics allowed for small violations of energy conservation (which sometimes people even say that it does, on short time periods, although this is not really correct), then McGonagall's tranformation would still violate physical law as we know it. In physics, you don't always push everything down to the most fundamental theory, which is a good thing, since we don't actually have a most fundamental theory of physics. There is no such thing as ‘our best [single] model of reality’; there are some ways in which our quantum models are (so far) worse than our classical ones.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 122, which is the final chapter of the story.
Happy once-in-a-century Pi Day! (3/14/15 == 3.1415)
There is 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. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)