The loop works because the conductor Harry that uses the Time-Turner at 6 PM is a younger version of the conductor Harry at 5 PM. Conductor Harry at 5:30 PM is going to go sit in the trunk at 6 PM, so he has no further need of the Time-Turner.
I think the most elegant formulation of a restriction that would prevent this (as well as all the things explicitly prevented in HPMoR) is that no path along which information or matter travels can stretch more than 30 hours per 24 hours.
So, you could put a 6-hour stretched pebble in someone's pocket, and they wouldn't be able to use a Time-Turner?
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 90. The previous thread has passed 750 comments.
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, 16, 17,18,19.
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: