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ChrisHallquist comments on Harry Potter and the Methods of Rationality discussion thread, part 17, chapter 86 - Less Wrong Discussion
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My guess is that this was a deliberate change. I always thought "cannot be blocked, except by inanimate objects!" was kinda lame.
Suddenly Quirrell's using it in the duel with Bahry is looking a lot weirder. What happens when he dodges it, does it go straight through the wall and keep on going indefinitely until it hits someone? Isn't that a massive liability since he risks someone seeing it, thereby giving away his presence?
Being able to be blocked by inanimate objects might seem "lame" for an epic forbidden spell, but being able to pass through solid matter like a jet of neutrinos turns it into yet another game-breakingly borkable element like the Bag of Holding. Combined with the Eye of Vance, Moody should mostly be able to avoid dueling in favor of sniping dark wizards through buildings.
This seems like an uncharacteristic failure by EY to think things through.
Maybe it hits a Dementor and that's how they reproduce.
Moody would have to take into account the coriolis non-force, at least for very-long-range shots. How fast does a killing curse move? Also, to what amount is a curse affected by curved space? Do they react to gravity at all?
It's not clear what it would mean to not be affected by curved space or gravity, since there's no "straight" besides geodesics and no "non-accelerating" besides freefall, but that doesn't seem to stop much in the HP verse.
Speaking of curved space, I've noticed that there are spells to make things bigger on the inside. If you do this just right, you can create a singularity known as a cone point that ought to send any spell fired at it back in the direction of the caster. Also, you could make a faster-than-light drive, which could be used as a time machine.
If the inertial mass of a spell is greater than its gravitational mass, it would appear that the spell doesn't react to gravity as much as it should. It is also possible that spells work a bit like brooms.
Gravity doesn't work that way. Something not reacting to gravity under general relativity is like something stopping under special relativity (or even Galilean invariance). However, considering that there's a spell that does just that, this doesn't mean much.
I hereby declare Arresto Momentum to match the velocity of a small mass to the velocity of some much larger mass that the wizard thinks is a reference frame.
Does that mean Harry can't use it (becuse there is no universal reference frame) or he can use it in all sorts of munchkiny ways (I stop the car ... relative to the moon!)
Well, for one thing, he's not powerful enough to cast it period, but if he were, I expect it would only work on near / nearest masses.
That requires original research, like partial transfiguration.
That's what I had in mind, yes.
So what would it do with a wizard who had truly internalized the principle of relativity, and who understood that there was no privileged reference frame? Could he use it to de facto impart an arbitrary velocity to an arbitrary object?
You can equalize velocity of a given small object with that of the caster's reference frame. The excess momentum is transferred to the Earth (or potentially another massive body, though there is no proof that magic works outside the Earth's atmosphere, which incidentally means that the Pioneercrux may have decayed). This way there is no preferred reference frame.
Of course there's no proof, but I don't think it's really possible, if only for literary reasons, that the Sphere of Stars spell is just a fancy hologram. I think we can take that as fairly strong evidence it's working as intended.
So "arbitrary" might be a bit strong, but what's to prevent him from using the Moon or the Sun as a reference frame? Or even the Earth as a whole, instead of the local part? Even imparting a relative 1000 mph to an object near the equator would be pretty powerful.
http://en.wikipedia.org/wiki/The_Billiard_Ball
You can't use Arresto Momentum for that; you need a much more massive object as a reference, but your reference frame only contains massless objects. I guess you could say that massless objects have much larger mass than other massless objects, and use Arresto Momentum to make photons go in arbitrary directions with negligible losses.
If you can make a surface cast a long-lasting Arresto Momentum, you have a near-perfect mirror for all wavelengths from radio to gamma and all angles. That would be useful. (Of course you can also make the light slower if you wish, but the fun you can have with arbitrary refractive indices with no wavelength dependence and no absorption is redundant here.)
Also, if we figure out the necessary ratio of masses at given magical energy, we can use the spell to measure mass. Assuming your aim is precise enough to Arresto Momentum a neutrino, anyway.
Magic works like the author of the story wants it to work.
I think it's safe to say that the HPMOR universe still runs on some sort of rules, even if they're not the usual ones Einstein taught us.
Actually, Eliezer has stated that he deliberately inserts impossible details in all his stories because he's disturbed by the notion that they might be simulated somewhere. I wouldn't expect it to affect the plot, though.
Didn't he say that he mentioned the time-turner because it disproves the simulation hypothesis? It would also guarantee that nobody would simulate it.
He seems to have figured out how to simulate it later, but that requires simulating everything, and there's no guarantee that there will even be a reality with a stable time loop, unless you have the infinite number of realities necessary to allow connectedness, in which case you can't possibly simulate all the possibilities.
Probably, but these are not mutually exclusive. If Dumbledore is right, the set of rules that the HPMOR world runs on are the laws of Narrative Causality.
You know that spell was invented for the film, right?
According to the wiki:
It looks to me like they established that there is a spell that does that, but it wasn't named until the movie. I suppose without the name there's no real evidence that it doesn't just accelerate the subject in any way the caster pleases.
In any case, in the MoR verse, the brooms act in a manner that involves some sort of rest state. Also, as of Eliezer's reply to this post, that spell canonically exists in the MoR verse.
Well, it's the name that actually tells us it's "arresting momentum" and not, I don't know, stopping him getting too close to the ground or some sort of anti-gravity spell. The scene is in the book, but the spell itself is not.
(The wiki treats the films a canon when they don't actually contradict the books, instead of a separate canon like most sane people would. They do the same for everything, in fact, from videogames to trading cards, although they draw the line at fanfiction.)
"Making things bigger on the inside" does not equal "bending space into any damn shape we please."
A cone point only requires being able to make things bigger on the inside. Just make a series of concentric spheres that are the right amount bigger on the inside and outside. If you don't make it smooth, it won't be perfect, but it just has to be good enough.
I don't know much about the faster-than-light stuff. From what I can find, an Alcubierre drive needs at least some negative mass, which, from what I understand, would translate to having to make things smaller on the inside. It seems likely that wizards would be able to make things smaller on the inside too, and they just don't do it much because it's pretty useless, at least for things wizards would think of.
Good point on the spheres, although I think Extension Charms are tied to enclosed spaces (hell, they might not even bend space. They could tap into another dimension or move you "out of phase" or something.)
Regarding the FTL, Alcubierre drives need a ring (or donut in the latest designs) of negative energy (or matter, I guess.) I can see that translating into "smaller on the inside" constructions, although I doubt there's actually a spell for that (although you never know.) Might be able to transfigure the stuff, though.
Perhaps that's just because no wizard is well-versed in non-euclidean geometry well-enough to understand how it would work in a non-enclosed space.
Besides, enclosed is relative. Maybe light doesn't travel through it, but neutrinos and your enemy's spells do.
It doesn't matter. As long as it takes longer to travel through, it works. For example, you could use different kinds of glass to make retroflectors using the same principle, since light will travel at different speeds.
Perhaps the same spell works. If the same spell could make something two or three times bigger on the inside, then why not one half times bigger?
What happens if you make it bigger on the inside and then turn it inside out?
Could be. Hard to tell without the author telling us.
I think most spells are disrupted by solid objects. And most offensive spells would risk destroying whatever you charmed. Would be interesting to try it on something made of glass, though.
Oh, I see. Cool. I assumed they were purely theoretical.
Interesting point. I doubt it works by specifying the increase as a number, though.
Hmm, there are probably other uses for containers with shrunken insides.
Inflatable mattresses (or waterbeds) that can be filled quickly/efficiently.
If rooms can be enchanted in this way (houses can certainly be bigger on the inside) then enchanting a long hallway in this way would allow people to walk longer distances in a short amount of time.
If the container is transparent, it could be used as a magnifying glass for things you placed inside.
In a sense they are. I've never seen anything about anybody actually doing that. I just know it would work in theory.
Lenses and optic fibers and such work on the same principle, but they aren't cone points.
Perhaps it has a range limit.
It would have to be significantly shorter than a lot of other spells have been shown to be (able to engage in ground-to-air combat against brooms) to be unable to target a person inside a building from outside it, or for a very large building like the castle of Hogwarts, at least from several rooms away.
Ordinary sniping relies on large amounts of distance between the shooter and the target to prevent them from being noticed and avoided or attacked. Moody could just rely on having multiple walls between him and his target.
Seems pretty obvious that a Killing Curse can't hit anyone but the intended target. You don't want dead that bystander you're not thinking about. Also "I meant to kill someone else" would be a defense if arrested for it.
Given that, it can fade quickly once it's moved past the target.
Hardly obvious to me.
Just the mood is required to cast it, the "small crack" at the soul. A killing beam is then launched. The beam keeps going until it reaches a killable target, which it very clearly is then implied to kill.
I always find it strange when people are reading so many implications that clearly aren't there, and are denying the implications that are...
No doubt they feel the same way.
I don't remember anything about the spell not being able to hit anything but the intended target, either in canon or the MoRverse. What's your source? Or, if there is no explicit source, what makes it "obvious"?
I just said. "You have to mean it", so it's odd that you could kill someone you didn't mean to. Even if you interpret it as "You have to want someone dead, not necessarily the same person", "if you're arrested for killing with it, there's no possible defense", and "I meant to kill the Death Eater, but I hit the bystander" is a possible defense. Also nobody ever mentioned collateral damage.
FWIW, "You have to want someone dead, not necessarily the same person" is essentially how "intent to kill" works in a legal sense. That is, the distinction between murder and manslaughter is whether, by your actions, you intended to kill someone; under the law, it doesn't matter whether the person actually killed was the person you intended to kill, or not.
Not that the rules of magic are necessarily modeled after modern US jurisprudence, but it might be that they both reflect a deeper moral concept.
What happens if Alice Attacker tries to kill you, and you try to kill her in self-defense, but end up killing Bob Bystander? The Killing Curse solves that one by having self-defense not count as intent to kill; does law do the same?
I think so (it's been quite a few years since my brief foray into law school). Let me do some quick Googling...
Yep, there it is: Looks like it may vary in different jurisdictions, but
Wanting to kill a specific person may be a requirement for fueling the spell, sure, but I don't see why that necessarily entails everyone else being immune to what is essentially a profoundly lethal effect. Once a bullet is in the air, it doesn't matter what motivated the firing of the gun.
The bit about nobody mentioning collateral damage sounds like an argument from silence. I'll tentatively grant you the point about "no possible defense", but to me it seems like Moody could well have been talking about deliberate, cold-blooded murder rather than all possible circumstances. I mean, by the time of the "no possible defense" line he's already name-dropped the Monroe Act, which is nothing if not a big, fat exception.
Well if you were using it fighting Death Eaters under the Monroe Act, and accidentally killed a bystander, and had fellow aurors to back up your story, you probably wouldn't be arrested.
Well, in the original canon, Voldemort fires one at Dumbledore, and Fawkes catches it and is reduced to a chick (phoenixes being unkillable.)
Of course, evidence from the original canon doesn't suggest it being able to pass through solid matter either, so that doesn't mean a whole lot with respect to HPMoR, but the spell would have to fade pretty damn quick to not be a liability for being spotted through a wall after missing. If it does it sounds like the best suggestion so far for resolving Quirrell's use of it in Azkaban, but that still leaves Moody able to snipe people through buildings.
So that's why Dumbledore set a chicken on fire - he was reviving Fawkes!
Sniper!Moody isn't a huge problem. Any halfway competent Dark wizard would plan for that kind of enemy (is the eye of Vance famous? anyway, anything that can help aim a Killing Curse through walls) and have wards in place to detect approaching and casting. It just makes walls transparent on both sides.
The Eye of Vance is well known enough that Moody was able to look it up and track it down, but not well known enough that he doesn't bother hiding facts such as its ability to see in a full sphere and through obstacles.
If wards can be put in place to detect approach with that kind of precision (evidence, the Marauder's Map, but that sort of thing may be beyond modern wizards, as it's part of Hogwarts' defense system and there's no other evidence of location scrying magic,) then you get an Avada Kedavra stalemate between Moody and anyone ensconced in a sufficiently well protected stronghold, but a complete mismatch between them and any of the vast majority of people who can't see through walls.
Considering that Moody was already a well known dark wizard hunter by the time he lost his eye, if the wielder can snipe people like this, it raises the question of how he got it from the person who had it in the first place. You'd expect a power hungry dark wizard to be able to use Avada Kedavra, and when you can actually see a full sphere around you through obstacles, it doesn't take a whole lot of creativity to notice that if you can use spells that go through obstacles, you can use it to attack people who can't see you.
For context, the original backstory:
So, it cost the very experienced Moody a great deal, and that was him going all out ('silly rules'). I don't think we can rule out that the "powerful Dark Wizard" wasn't effectively employing the omniscience of the Eye.
Shooting someone with Avada Kedavra through a wall isn't going to result in the loss of any body parts though, and can be employed before face to face engagement is even an option, unless Moody had some way of teleporting straight into the wizard's stronghold, which would imply some pretty lousy security.
If the Eye of Vance lets you AK people through buildings, I wouldn't think the added security of having it would be worth enough to Moody to overcome the risk of trying to acquire it, which would probably be phenomenal unless whoever had it before was an idiot.
It could be used to force other actions, per Quirrel's excuse to Harry, and the forced choices lead to limb loss.
It's much harder though, to dodge a bolt that comes straight out of a wall without any warning because you can't see the person who fired it, who if they have much sense has deliberately moved around so that they're not only attacking from a point where you can't see them or fire back, but from an angle where you won't see the beam either.
All the best ways I can think of to take the magical eye from someone who can do that, and lives in a place without "silly rules" against actually doing it, wouldn't place me in a position to lose limbs in the encounter. If he's not as Constantly Vigilant as Moody, he might be poisoned, but assuming it wouldn't destroy the eye or render it unretrievable, I'd sooner call in an airstrike. Although it's chronologically too early for transfigured predator drones, which would be my top choice.
Moody can still dodge.
That is not obvious at all, at least to me. Or Harry, who seemed to interpret it in terms of risk to bystanders.
"When" he dodges it? This seems like strong evidence that Q knew he wouldn't.
An interesting point. Do we know that he doesn't, in cases where he wants them dead as an end in itself?
I'd be surprised if Quirrell isn't competent enough to be able to judge effectively if his opponent is going to be able to dodge his attack, and Bahry thought he was going to be able to dodge it. Killing a guard would be a bad idea (if he's still alive he can be obliviated without blowing a hole in their security,) so if the spell travels through walls it seems like a dumb move whether it hits or not.
We don't know for a fact that Moody doesn't snipe dark wizards through buildings, but if he did I'd think it would have been mentioned even with the small amount of stage time Moody's had so far.
Could be that the bolt just doesn't move that fast. If it's possible to dodge at close range (like Bahry?) then it would have to move fairly slow.
Well, we don't know just how close they were, but if it were all that slow people wouldn't even bother using it in combat. I tend to assume that fired spells are somewhere in the ballpark of fastball speed.
A spell that can be dodged with difficulty when fired by an opponent you're dueling should be more than a little more difficult to dodge if it comes without warning out of a wall behind you though.
So if you fire it at the ground, can you kill someone on the other side of the Earth? Not being blocked by inanimate objects is kinda lame too.
Don't worry, the power drops off with the inverse square of the distance. It's lethal at pretty much any reasonable range, but then drops off quickly after a half mile or so.
I just made that up.
Actually, it spreads as an Airy disc, which gives it a radius of about 300 metres at the far side of the planet, and the effect is divided among all the souls it hits. If you hit a city on the other side of the planet, you just take a couple days off everybody's life. (The technical term is "statistical homicide")
That would make sense as a general rule for spells, otherwise why do they bother having duels face-to-face rather than sniping from nearby mountains? (Or an invisible broomstick 2000m up..)
You do have to aim it by hand and eye. You try hitting a human-sized target from a moving platform at 2km.
Given the descriptions of wandwork we've seen in canon and in MoR so far, I imagine it'd be difficult to reliably hit anything person-sized past thirty feet or so. You can't sight down a wand if you have to swish and flick (though a wizard's staff with a telescopic scope mounted on it is a nice Discworldly image), so it should be about as accurate as throwing a ball -- which is to say not very.
We know of at least one spell that aims itself (Flitwick's) and area affect spells are possible (with a massive fireball it doesn't matter how you aim).
Alternatively, take a potion of +10 accuracy or the equivalent.
Felix Felicis may be the only potion that performs that function, and it's sufficiently broken to be the Potion Not Appearing In This Fic.
Just find something that was made by using up a lot of accuracy. That should do it.
A target with nothing but bulls-eyes will do.
You would have to get extremely (un)lucky to do so. A human, lying down, takes up about 1 m^2 of space. Even if you fired it at a city with a population density of 10000 people/km^2, you'd still only have about a 1% chance of hitting someone (if you could even aim well enough to hit a city from 12000 km away).
Like an ordinary muggle missile, KC was designed with a built-in self-destruct mechanism, which is activated when its target is not hit. Thus you die if you block a curse aimed at someone else, but not if the curse misses the target and you happen to be in its path.
This. If not this, Moody is lying, which is possible, as Moody is the type to keep information like that "in reserve", but I actually doubt that is the case, as sooner or later Harry would witness for himself a killing curse being cast, and would find that Moody had been lying.
Also, I doubt that everyone else in the room was either clueless or willing to let Harry receive such massively incorrect info.