It may be better to put it like this: "if there are many worlds, then time travel would generally create loops across worlds; it does not force consistency within a single world".
However, if the Source of Magic is careful how it sets up the loops, it can force a consistent outcome, or at least force one of the consistent outcomes to become much more probable than any inconsistent outcome (one which loops between worlds). In particular this still allows any NP problem, or indeed any PSPACE problem, to be solved in polynomial time using tricks like Harry's factorisation attempt (though perhaps with a small probability of failure). See Scott Aaranson's wonderful lecture here.
So the fact that Harry always observes a consistent single-world loop doesn't by itself imply a single world interpretation, or any non-computability. It simply means that the Source of Magic is a PSPACE oracle!
The next discussion thread is here.
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 85. The previous thread has long passed 500 comments. Comment in the 15th thread until you read chapter 85.
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. (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.)
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: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15.
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: