Harry Potter and the Methods of Rationality discussion thread, February 2015, chapter 110

Gondolinian

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 110.

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:

You do not need to rot13 anything about HP:MoR or the original Harry Potter series unless you are posting insider information from Eliezer Yudkowsky which is not supposed to be publicly available (which includes public statements by Eliezer that have been retracted).

If there is evidence for X in MOR and/or canon then it’s fine to post about X without rot13, even if you also have heard privately from Eliezer that X is true. But you should not post that “Eliezer said X is true” unless you use rot13.

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 110.

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:

You do not need to rot13 anything about HP:MoR or the original Harry Potter series unless you are posting insider information from Eliezer Yudkowsky which is not supposed to be publicly available (which includes public statements by Eliezer that have been retracted).

If there is evidence for X in MOR and/or canon then it’s fine to post about X without rot13, even if you also have heard privately from Eliezer that X is true. But you should not post that “Eliezer said X is true” unless you use rot13.

The mirror and efficient simulation

Until the mirror appeared, the HPMOR universe could be simulated efficiently, at least as far as we knew. Time travel is limited to a six-hour cache; you can't transfigure arbitrary things, and Harry's attempts to use time travel to solve computational problems failed. This is likely to be deliberate.

So, how does the mirror exist? According to the inscription on the back, the mirror shows the actor's coherent extrapolated volition (CEV). Is this possible to compute efficiently from an actor's source code? I would guess not. (Is this right? Is there a hardness proof?)

Here are some possibilities to preserve efficient simulation:

The mirror is a trick and doesn't do what it says it does
Perhaps the NPCs are programmed to have known CEVs
Causality goes in the other direction. Computing the CEV from the source is hard, but constraining an actor to act in a way consistent with their CEV might not be. Perhaps everyone's CEV is set when they first look in the mirror, and then they are constrained to act in accordance with this. (This is somewhat akin to the way of avoiding paradoxes in a quantum universe with time travel, whereby if you go back in time and shoot your grandmother, the bullet diffracts around her.)
Maybe the previous item is only true of the NPCs. Is the mirror blank at the end of 110 because Harry is a PC (alternatively: simulating him is the purpose of simulation) and computing his CEV is too hard?

Self-consitant time travel seems far harder to simulate than CEV.