Harry Potter and the Methods of Rationality

hoped that he'd just achieved fusion with his mysterious dark side and would be enabled to draw on all of its benefits with none of its drawbacks, call up the crystal clarity and indomitable will on demand, without needing to go cold or angry.

Once again, he'd overestimated how much progress he'd made. Something had happened, but Harry still had a mysterious dark side, it was still separate from him, and his ordinary self was still domitable. And despite the repair work he'd done on his dark side's fear of death, he didn't dare go dark while unshielded in Azkaban, that was tempting fate way too much.

Which was unfortunate, because a bit of nondomitability would have sure come in handy about now.

What made it harder was that he couldn't slump against a wall, couldn't break into tears, couldn't even heave a sigh. His dear Bella was watching him and that wasn't the sort of thing her Dark Lord would do.

'My Lord -' Bellatrix said. Her low voice was strained. 'The Dementors - they are coming - I can feel them, my Lord -'

'Thank you, Bella,' said a dry voice, 'I already know that.'

Harry couldn't sense the holes in the world the same way as when he'd been wearing the Deathly Hallow, but he could feel the empty pull increasing in intensity. At first he'd mistaken it for the result of descending a stairwell, until he and Bellatrix had finished descending and the pull had gone on increasing. Then decreased, as the Dementors moved away along the spiral, then increased as they went up another flight of stairs... There were Dementors within Azkaban itself now, and they were coming for him. Of course they were. Harry might be resistant now, but he was not hidden.

New requirement, Harry told his brain. Find a way of defeating Dementors that doesn't invoke my Patronus Charm. Alternatively, find yet another way of hiding someone from Dementors, besides the Cloak of Invisibility -

I quit, said his brain. Find yourself another piece of computing substrate to solve your ridiculously overconstrained problems.

I mean it, thought Harry.

So do I, said his brain. Put up your Patronus Charm and wait for the Aurors to find you. Be sensible. It's over.

Give up...

The sucking emptiness seemed to pull harder, as he thought it; and Harry realized what was happening, concentrated more intensely on the stars, turned his mind away from the despair -

You know, observed the logical side of him, if you're not allowed to think any negative thoughts because that will open your mind to the Dementors, that's a cognitive bias too, how would you know if it actually was time to give up?

A desperate sobbing scream rose up from below, words mixed in like 'no' and 'away'. The prisoners knew, the prisoners could feel it.

The Dementors were coming.

'My Lord, you - you should not risk yourself for me - take back your Cloak -'

'Be silent, fool,' hissed an angry voice. 'When I decide to sacrifice you I will tell you so.'

She's got a valid point, said Slytherin. You shouldn't risk yourself for her, there's no way her life is as valuable as yours.

For an instant Harry considered sacrificing Bellatrix to save himself -

And in that moment, some of the dim orange gas-light seemed to flee the corridor, a touch of cold crept over Harry's fingertips. And he knew, then, that to think of leaving Bellatrix to the shadows of Death, would make him vulnerable once more. Even in the moment of making the decision, he might become unable to cast the Patronus Charm, for he would have given up the thought that had saved him before.

It occurred to Harry that he could still take the Cloak from Bellatrix afterward, even if he couldn't cast the Patronus Charm; and then he had to wrench his thoughts away from that option, focus firmly on his decision not to do it, or he might have just fallen over where he stood. For the whirlpool of emptiness swirling around him was now deadly strong; there were screams coming from above, and the screams below had stopped.

This is ridiculous, said his logical side. Rational agents shouldn't have to put up with this sort of censored reasoning process, all the theorems assume that how you think doesn't affect reality apart from your actual actions, which is why you're free to choose an optimal algorithm without worrying about how your thoughts interact with Dementors -

...

That is a really dumb idea, said Gryffindor. Even I think it's a dumb idea and I'm your Gryffindor side. You're not seriously going to just stand there and -

'We have a fix!' shouted Ora, holding up her magic mirror as though in triumph. 'The Dementor outside the inner wall pointed to level seven, C spiral, that's where they are!'

Her Aurors were looking at her expectantly.

'No,' Amelia said in a level voice. 'That's where one of them is. The Dementors still can't find Bellatrix Black. We are not running down there and letting her through in the confusion, and we are not dividing our forces to be ambushed. So long as we move with caution, we can't lose. Tell Scrimgeour and Shacklebolt to keep going down level by level, same as before -'

The old wizard was already striding forward. Amelia didn't even bother cursing him, this time, as once again their carefully constructed shields parted like water and rippled gently in his wake.

Harry waited at the beginning of the corridor, just next to the stairs leading upward. Bellatrix and the snake were behind him, concealed by the Deathly Hallow that Harry had mastered; he knew, though he could not see, that the emaciated sorceress was sitting upon the stairs, slumped back, since Harry had withdrawn his Hover Charm to free