I am amazed that Eliezer managed to take Rowling's most corny idea and made it non-corny: "The power that the Dark Lord knows not" is, after all, none other than the power of true love. And it is a mighty power not because of a hokey magical force attached to it, but because someone who feels it in addition to being rational is motivated to reshape the universe. "Power comes from having something to protect."

For those wondering about this:

It has been three hundred and twenty-three years since the country of magical Italy was ruined by one man's folly.

323 years before 1992, this happened:

Etna's most destructive eruption since 122 BC started on 11 March 1669 and produced lava flows that destroyed at least 10 villages on its southern flank before reaching the city walls of the town of Catania five weeks later, on 15 April. The lava was largely diverted by these walls into the sea to the south of the city, filling the harbour of Catania. A small portion of lava eventually broke through a fragile section of the city walls on the western side of Catania and destroyed a few buildings before stopping in the rear of the Benedictine monastery, without reaching the centre of the town.

That's probably also what's referenced later on:

There is much literary wisdom in those stories. It is born of harsh experience and cities of ash.

(though it's pretty likely that in HPMOR-verse, all volcano eruptions, earthquakes, tsunamis, etc. are caused by Magic Gone Wrong)

A while ago Mitchell Porter wrote that Robin Hanson often makes arguments like:

People claim that they want to be smart and would like to be smarter. But if you stand on your head, blood pools in your brain, providing more oxygen, and thus improving your cognitive function. Yet people spend hardly any time standing on their heads. Does this mean that they don't really want to be smarter?

Quirrel is being even more Hansonion than usual in #95, arguing that other people not trying to raise their friends from the dead means they don't care about their friends.

Piece of meta info:

V'ir vagebqhprq n grrantr sevraq gb UCZBE. Ure cevbe ernqvat sbphf fheebhaqf Qvpxraf naq Nhfgra naq gur yvxr. Fur unfa'g ernq YJ lrg. Fur'f whfg ernq gur arj puncgre. Univat abg ernq gur bayvar qvfphffvbaf be Nhgube'f Abgrf jungfbrire, fur qbrf abg xabj nobhg Ibyqrzbeg.

Vg vf bayl ng gur raq bs guvf, Puncgre 95, gung fur unf gubhtug hc gur cbffvovyvgl frevbhfyl.

Znal crbcyr unir orra jbaqrevat jul Uneel unfa'g znqr gur pbaarpgvba, naq V jnagrq gb funer guvf qngn cbvag bs fbzrbar ryfr jub qvqa'g unir gur Jbeq bs Tbq. Bs pbhefr, fur vfa'g Engvbanyvfg!Uneel, ohg gur qngn vf vagrerfgvat.

I didn't cry in "Humanism." I didn't cry in "Stanford Prison Experiment." I didn't even cry when Hermione died. But this chapter finally did it for me. "If I were the first person in the universe who ever really cared about someone, then I'd be honored to be that person." That's the kind of moral stand missing in any number of lectures and parables by supposed moral absolutists. It takes quite a bit of deviation from normal thinking to even really comprehend that emotion, let alone spontaneously describe it.

What I love best about HPMOR is that it could so easily have been a Kid Hero parody fic, and even though it skirts pretty close, especially in the earlier chapters, it is never quite a straight up parody. In fact, for all that Harry snarks about his life being one big fantasy cliche, HPMOR takes the Kid Hero genre deadly seriously and plays almost every trope completely straight. Sure, Harry doesn't rush headlong into every danger like most kid heroes, but that's a difference in method, not in spirit. He feels the weight of responsibility just like anyone else who was ever chosen, or chose themselves.

Far more than the science and even the rationality, I love HPMOR because it believes in heroes. Conversations like this one are why I'm not reading a textbook. One day, I'm going to catalog every single discussion about morality, duty, heroism, or wisdom. I genuinely think reading them often will make me a better person, or at least better at being good. So thank you, Eliezer. You really make fiction shine as a teaching medium

Some conjectures on the nature of magic, the invention of new spells, etc.:

1. Whatever makes magic work is basically mechanical but smart enough to be sensitive to human intentions.

2. It has to do something broadly comparable to simulating the universe.

3. It is equipped with defensive measures of one or more of the following kinds. (a) Some things -- e.g., certain kinds of escapades involving Time-Turners -- would require excessive, possibly infinite, amounts of computation, and it won't allow that. (b) Some things -- again, including Time-Turner abuse -- actually lead to contradictions. Maybe those are caught in advance and prevented, or maybe those simulations just end when the contradiction is reached. (c) There are deliberate countermeasures against anything that looks like it's trying to marshal too much power, in case it's an attempt at hacking the underlying computational substrate (or whatever it is that makes magic work).

4. That is one reason why inventing new spells is dangerous. You might accidentally produce a contradiction or an excessively expensive simulation, or you might do something that looks like an attempt at becoming a god, in which case you -- or your laboratory -- or your country -- or your universe -- is terminated with extreme prejudice.

5. It is also why the most powerful magics -- the rituals -- require permanent sacrifices: something that involves a permanent sacrifice is harder to apply recursively in some weird way that turns it into a Become God spell. (It's like the way that the class of functions you can compute using only loops whose number of iterations is bounded in advance is smaller and easier to prove things about than the class of all functions you can compute.)

6. Whatever-makes-magic-work wasn't programmed in advance with any particular spells, potions, etc.; it's a general-purpose magic substrate. All the specific things have been brought into being by human beings -- it's a gigantic game of Nomic. That is why, e.g., all the spells have names that were obviously thought up by humans.

7. The words, gestures, etc., are likewise basically under the control of the inventors. That is why they can be stupid things like "Wingardium Leviosa", or require you to say "Oogely boogely" with just the right timing. (Perhaps the precision required is up to the inventor, or perhaps whatever-makes-magic-work decides how much precision to require on the basis of how powerful the magic is.)

8. Bringing a new magic into being isn't fundamentally difficult [EDITED to add: that would explain why there is such a thing as "the usual evasions" when someone asks precocious questions about spell creation]; perhaps it just requires forming a certain sort of intention and then demonstrating what actions (etc.) are required to bring about the desired effect. The difficulty and danger come (a) from the protective measures already mentioned, (b) from the risk that when you tell whatever-makes-magic-happen what you want you might fail to be specific enough and get something that meets your stated spec but is disastrous, and (c) from restrictions like one I mention below.

9. Maybe the heritability of access to magic is itself a thing that was decided by (a much earlier generation of) humans, perhaps as a deliberate measure to limit the number and increase the cohesion of those designing new magics.

10. How would this sort of general-purpose Everything Machine likely be set up, so as not to produce a universe of total chaos as everyone starts inventing their own new spells? (Even assuming no one is able to do anything too destructive or internally inconsistent, on account of the sort of restrictions I already mentioned.) Probably by having a requirement that new spells be consistent with existing ones, in some rather broad sense of "consistent". That would be another reason why inventing new magic is difficult. It might also give another reason for things like the Interdict of Merlin: an opportunity for old magic to be "garbage-collected", freeing up regions of possible-magic-space for new generations to explore.

I don't assign a super-high probability to any of these, but I find each more plausible than any other similarly-specific alternative I've thought of.

On Quirrell's theory of human nature:

It seems to me that in general, his theory yields pretty accurate predictions, and to see what's wrong with it you probably need to know some evolutionary psychology; Eliezer's Adaptation-Executers, not Fitness-Maximizers. Evolution is going to favor genes for convincingly acting like you care about your friends without incurring too many costs for their sake. Yeah, it's also going to favor genes for seeing through easily faked signals, but to the extent that people can get away with it, it's going to favor genes for seeming to care about your friends without incurring the costs that would go along with that. The twist is that evolution while evolution produces behaviors that tend in that direction, it doesn't produce creatures who follow the strategies exactly, or consciously. The result is people who actually care about their friends... even if they very often don't act like it.

I am confused. You know how Dumbledore expresses several times to McGonagall his worry that he might be the Dark Lord Harry will need to face? I mostly thought this was simply guilt from having had to make lots of difficult decisions.

But I’ve been re-reading some older chapters today, and I noticed this (ch. 84):

“Indeed—indeed—that will be necessary and more than necessary, if the Dark Lord that Harry must defeat to come into his power is not Voldemort after all—”

“Not this again!” Minerva said. “Albus, it was You-Know-Who, not you, who marked Harry as his equal. There is no possible way that the prophecy could be talking about you!”

The old wizard nodded, but his eyes still seemed distant, fixed only on the road ahead.

What Minerva says sounds a lot like foreshadowing. More specifically, standard dramatic logic would suggest that it was actually Dumbledore who gave Harry the mark, thus justifying D’s fears and making Minerva’s reasoning exactly wrong on the point she is most sure about. There’s plenty suspicious about the “standard story” of what happened that night to allow it, and nothing else I know about Dumbledore sounds like something that would cause serious Dark-Dumbledore worries.

But that doesn’t seem to make sense at all with the rest of the story. Am I just reading too much because of theories I read here?

Quirrell seems to have been counterfactually mugged by hearing the prophecy of the end of the world...which would mean his decision theory, and psychological commitment to it, are very advanced.

Assume Quirrell believes that the only possible explanation of the prophecy he heard is that the apocalypse is nigh. This makes sense: prophecies don't occur for trivial events like a visitor to Hogwarts destroying books in the library named "Stars in Heaven" and "The World," and the idea of "the end of the world" being a eucatastrophe hasn't occurred to him. Assume Quirrell believes that prophecies are inevitable once spoken. Then why is Quirrell bothering to try to save the world?

Given that he hears the prophecy, Quirrell can either try T or not try ~T to avert it. Given that he tries, Quirrell is either capable C or incapable ~C of averting it. If T and C, by inevitability Quirrell will never hear the prophecy, which means that it is less likely the end of the world will occur (massive events always produce a prophecy that is heard by a wizard, so either Time finds some way to stop the end of the world or someone else hears it but fails to avert it). Say the end of the world causes -100 utility to Quirrell, and trying to stop it causes -1 utility. Then if C, a Quirrell that would try never hears the prophecy, so he never loses any utility, while a Quirrell that would not try hears the prophecy, goes out in a blaze of hedonism rather than fighting the inevitable, and loses 100 utility from the end of the world. Unfortunately, the actual world is the ~C world, where T brings -101 utility and ~T brings -100. So T looks like an irrational choice, but actually maximizes Quirrell's utility across counterfactuals.

This isn't the only explanation for Quirrell's actions; he could just prefer to go out fighting, or be betting on the slim chance that prophecies actually can be averted, or just trying to delay the end of the world as long as possible, or acting on other, weirder motives. But it's an interesting illustration of how alien a being that has truly internalized a really sophisticated decision theory might be.

Professor Quirrell took a small step to the left, a step forward, another to the right. He tilted his head with a look of calculation, and then he walked almost directly towards where Harry stood, halted a few paces off with the sense of doom enflamed to the height of bearability.

Nice, Quirrell is tracking Harry by checking in which direction the sense of doom becomes stronger.

I hereby rechristen "the sense of doom" to "the sensor of doom".

Edit: "But what do Muggles know of true power? It is not them who frightens me now. It is you." Typo, should be 'frighten'.

Edit 2: "I could name a dozen examples in Muggle novels of people driven to resurrect their dead friends. The authors of those stories clearly understood exactly how I feel about Hermione. Though you wouldn't have read them, I guess... maybe Orpheus and Eurydice?" -- Aah, what a lost chance to break the fourth wall and cite HPMOR as an example!

I just realized that Harry does not worry about Hermione's body disappearing anywhere I can remember in this chapter, which tells me he either knows exactly what's going on, or he plans to ignore the direct route and just become god, and thus it doesn't matter.

Or maybe find a worthy Muggleborn in a country that didn't identify Muggleborn children, and tell them some extensive lies, fake up a surrounding story and corresponding evidence, so that, from the very beginning, they'd have a different idea of what magic could do.

Pretty sure this is Jean-Jacques Rousseau's strategy in Emile. Albeit for social-sexual development, instead of magic.

After sitting down and going over everything I know about this fic, I believe I've gotten a substantial way towards solving its puzzles. The long version is at my blog here, but here I'll just state without justification the prediction I've come up with:

Voldemort believes fate won't let him defeat Harry until Harry attains the power to vanquish him, which in this case means becoming powerful enough to destroy all of Voldemort's well-hidden horcruxes. And in fact, Harry will become that powerful, by using the differing conservation laws for magic and science to conduct conservation-law arbitrage. Voldemort's plan is to possess Harry once Harry has attained ultimate power, but Harry will prevent Voldemort from winning through complicated means involving multiple currently yet-to-be-fired Checkov's guns.