Prediction: Atlantis wasn't a catastrophe that the Mirror was too late to avert. Rather, the Mirror was completed, and the Atlanteans removed themselves to a realm of existence within the Mirror. Confidence: 5%.
Far more likely that there was a catastrophe, and the Mirror itself was the cause.
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 109.
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.)
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: