Harry Potter and the Methods of Rationality

It wasn't like modern-day Muggles had gotten anywhere near the limits of what Muggle physics said was possible. And yet, like the ancient hunter-gatherers conceptually bound to their rock-throwers, most Muggles lived in a world defined by the limits of what you could do with cars and telephones. Even though Muggle physics explicitly permitted possibilities like molecular nanotechnology or the Penrose process for extracting energy from black holes, most people filed that away in the same section of their brain that stored fairy tales and history books, well away from their personal realities: Long ago and far away, ever so long ago. It was no surprise at all, then, that the wizarding world lived in a conceptual universe bounded - not by fundamental laws of magic that nobody even knew - but rather by the surface rules of known Charms and enchantments. You couldn't observe the way magic was practiced nowadays and not be reminded of the National Museum of Australia, once you realized what you were seeing. Even if Harry's first guess had been mistaken, one way or another it was still inconceivable that the fundamental laws of the universe contained a special case for human lips shaping the phrase 'Wingardium Leviosa'. And yet even that fumbling grasp of magic was enough to do things that Muggle physics said should be impossible: the Time-Turner, the water conjured out of nothingness by Aguamenti. What were the ultimate possibilities of invention, if the underlying laws of the universe permitted an eleven-year-old with a stick to violate almost every constraint in the Muggle version of physics?

Like a hunter-gatherer trying to look up at the Sun, and guess that the universe had to be shaped in a way that allowed for nuclear energy...

It made you wonder if maybe twenty thousand million million million meters wasn't so much distance, after all.

There was a step beyond Abstract Reasoning Harry which he could take, given time enough to compose himself and the right surroundings. Looking up at the stars, you could try to imagine what the distant descendants of humanity would think of your dilemma - in a hundred million years, when all the visible stars would have rotated through great galactic movements into entirely new positions, every constellation scattered. It was an elementary theorem of probability that if you already knew what your answer would be after updating on future evidence, you ought to adopt that answer right now. If you knew your destination, you were already there. And by analogy, if not quite by theorem, if you could guess what the descendants of humanity would think of something, you ought to go ahead and take that as your own best guess.

From that vantage point the idea of killing off two-thirds of the Wizengamot seemed a lot less appealing than it had a few hours earlier. Even if you had to do it, even if you knew for a solid fact that it would be the best thing for magical Britain and that the complete Story of Time would look worse if you didn't do it... even as a necessity, the deaths of sentient beings would still be a tragedy. One more element of the sorrows of Earth; the Most Ancient Earth from which everything had begun, long ago and far away, ever so long ago.

He is not like Grindelwald. There is nothing human left in him. Him you must destroy. Save your fury for that, and that alone -

Harry shook his head slightly, tilting the stars a little in his vision, as he lay on the stone floor looking upward and outward and forward in time. Even if Dumbledore was right, and the true enemy was utterly mad and evil... in a hundred million years the organic lifeform known as Lord Voldemort probably wouldn't seem much different from all the other bewildered children of Ancient Earth. Whatever Lord Voldemort had done to himself, whatever Dark rituals seemed so horribly irrevocable on a merely human scale, it wouldn't be beyond curing with the technology of a hundred million years. Killing him, if you didn't have to do it, would be just one more death for future sentient beings to be sad about. How could you look up at the stars, and believe anything else?

Harry stared up at the twinkling lights of Eternity and wondered what the children's children's children would think of what Dumbledore had maybe-done to Narcissa.

But even if you tried framing the question that way, asking what humanity's descendants would think, it still drew only on your own knowledge, not theirs. The answer still came from inside yourself, and it could still be mistaken. If you didn't know the tenth decimal digit of pi yourself, then you didn't know how the children's children's children would calculate it, for all that the fact was trivial.

Thoughts came to Harry's mind, then, elements of the vast stored wisdom and the thousand other lives that lay within his parents' science fiction collection. There might be other reasons why Harry sometimes seemed older than his physical age, but all those fictional lives he'd lived had probably also played a role. Harry might not be able to remember the exact words, like Hermione could, but he remembered the sense.

In the mirrors of the many judgments, my hands are the color of blood. I sometimes fancy myself an evil which exists to oppose other evils; and on that great Day of which the prophets speak but in which they do not truly believe, on the day the world is utterly cleansed of evil, then I too will go down into darkness, swallowing curses. Until then, I will not wash my hands nor let them hang useless.

Corwin of Amber.

There will always be some that cannot be saved.

If I must sacrifice five hundred to save one thousand -

Then I will abandon one hundred and earn nine hundred.

But still -

I believed someone would be a superhero if they saved everyone even though they thought like that.

It might be an idealistic concept or an impossible pipe dream, but a superhero is someone who tries to save everyone in spite of that.

Emiya Shirou.

No words can prevent all killing. Words are not iron bands. But I taught you to hesitate, to stay your hands until the weight of duty crushed them down.

Anansi the Spider.

Harry took in a breath of the cold night air, and said, quietly into the night, 'All right.'

Slowly - he'd probably been lying there, looking at the stars, for longer than he'd thought - Harry sat up from the ground. Pushing himself to his feet, the muscles protesting, he walked over to the edge of the stone platform at the height of the Ravenclaw tower. The stone crenellations surrounding the edge of the tower weren't high, not anywhere near high enough to be safe; they were there more as a marker, clearly, than as a railing. Harry didn't approach too close to the edge; there was no point in taking chances. Looking down at the Hogwarts grounds below, he was predictably feeling a sense of dizziness, the wobbly affliction called vertigo. His brain was alarmed, of course, because the ground below was so distant. It might have been fully 50 meters away.

I will make a bargain with myself, Harry said to within himself, to all his parts. I will follow the path of the superhero as far as I can. But if I can't - if