ETA: gjm is right: Voldemort himself says the target must be either willing or too weak to resist him. So Voldemort can't possess most random people, and certainly not Dumbledore.
If Voldemort could possess Dumbledore, he could have done so earlier and simply given himself the Stone, as well as the Elder Wand and any other interesting gadgets Dumbledore has. He'd have made Dumbledore teach him all the spells he knows, too, if those survive possession. And he'd have used Dumbledore to attack by surprise Flamel or anyone else if he wanted to.
In the least convenient world, possessing someone doesn't give Voldemort access to any of their previous memories or spells, it just wipes the mind and takes over the body. Then it might be hard to possess Dumbledore and use him to get the Stone. But he could still take out Dumbledore, cause Flamel to remove the Stone from Hogwarts, and then possess Flamel while he has the Stone.
Possessing anyone in the world (or at least, any wizard other than Harry) just by making them touch any object you prepared beforehand is so overpowered that if it's true, the only possible reason Quirrel is still plotting anything or playing games or appearing to ever be in danger, is that he'd be bored otherwise.
If Voldemort can possess Dumbledore at will and chooses not to, the only reason I can think of is that it would make the game too boring, like he said about the Wizarding War. This strikes me as... inadequate. With the Stone involved, Voldermort is playing for real stakes, and waiting for the end of the year increases the chance something will go wrong, weakens the Quirrel body, and eventually forces Voldemort to operate on the last day of the school year, when others might guess something important would happen.
(Edited:) But why wouldn't Voldemort be able to possess Dumbledore, or anyone else in the world, other than Harry? He claims the only requirement is to have the target touch a Horcrux 2.0. This seems fairly easy: to give make sure your target will touch a Horcruxed coin, you can just toss them one and they will catch it by reflex, as an earlier chapter pointed out. And you can horcrux the doorknob of their office, a chair they'll sit on in a public park, etc. It may be, however, that since Voldemort has only had this ability for a few months, during which Dumbledore has been on high alert, he hasn't been able to accomplish this yet.
I just realized Voldemort probably cast the revised Horcrux on Roger Bacon's diary with wordless magic:
The book vanished back into Professor Quirrell's robes, and he rose up from his chair. Professor Quirrell started to walk over to the door -
- and staggered, suddenly lurching into the wall.
"It's all right," said Professor Quirrell's voice, which suddenly sounded a lot weaker than usual. "Sit down, Mr. Potter, it's just a dizzy spell. Sit down."
[...]
..."That, Harry Potter, is the diary of Roger Bacon."
Harry almost fainted
New long chapter! Since I expect its discussion to generate more than 160 comments (which would push the previous thread over the 500 comment limit) before the next chapter is posted, here is a new thread.
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 108
(and chapter 109, once it comes out on Monday).EDIT: There have now been two separate calls for having one thread per chapter, along with a poll in this thread. If the poll in this thread indicates a majority preference for one thread per chapter by Monday, I will edit this post to make it for chapter 108 only. In that case a new thread for chapter 109 should be posted by whoever gets a chance and wants to after the chapter is released.
EDIT 2: The poll indicates a large majority (currently 78%) in favor of one thread per chapter. This post has been edited accordingly.
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: