Harry Potter and the Methods of Rationality

to levitate something, because, come on, 'Wingardium Leviosa'? The universe was going to check that you said 'Wingardium Leviosa' in exactly the right way and otherwise it wouldn't make the quill float?

No. Obviously no, once you thought about it seriously. Someone, quite possibly an actual preschool child, but at any rate some English-speaking magic user, who thought that 'Wingardium Leviosa' sounded all flyish and floaty, had originally spoken those words while casting the spell for the first time. And then told everyone else it was necessary.

But (Harry had reasoned) it didn't have to be that way, it wasn't built into the universe, it was built into you.

There was an old story passed down among scientists, a cautionary tale, the story of Blondlot and the N- Rays.

Shortly after the discovery of X-Rays, an eminent French physicist named Prosper-Rene Blondlot - who had been first to measure the speed of radio waves and show that they propagated at the speed of light - had announced the discovery of an amazing new phenomenon, N-Rays, which would induce a faint brightening of a screen. You had to look hard to see it, but it was there. N-Rays had all sorts of interesting properties. They were bent by aluminium and could be focused by an aluminium prism into striking a treated thread of cadmium sulfide, which would then glow faintly in the dark...

Soon dozens of other scientists had confirmed Blondlot's results, especially in France.

But there were still other scientists, in England and Germany, who said they weren't quite sure they could see that faint glow.

Blondlot had said they were probably setting up the machinery wrong.

One day Blondlot had given a demonstration of N-Rays. The lights had turned out, and his assistant had called off the brightening and darkening as Blondlot performed his manipulations.

It had been a normal demonstration, all the results going as expected.

Even though an American scientist named Robert Wood had quietly stolen the aluminium prism from the center of Blondlot's mechanism.

And that had been the end of N-Rays.

Reality, Philip K. Dick had once said, is that which, when you stop believing in it, doesn't go away.

Blondlot's sin had been obvious in retrospect. He shouldn't have told his assistant what he was doing. Blondlot should have made sure the assistant didn't know what was being tried or when it was being tried, before asking him to describe the screen's brightness. It could have been that simple.

Nowadays it was called 'blinding' and it was one of the things modern scientists took for granted. If you were doing a psychology experiment to see whether people got angrier when they were hit over the head with red truncheons than with green truncheons, you didn't get to look at the subjects yourself and decide how 'angry' they were. You would snap photos of them after they'd been hit with the truncheon, and send the photos off to a panel of raters, who would rate on a scale of 1 to 10 how angry each person looked, obviously without knowing what color of truncheon they'd been hit with. Indeed there was no good reason to tell the raters what the experiment was about, at all. You certainly wouldn't tell the experimental subjects that you thought they ought to be angrier when hit by red truncheons. You'd just offer them 20 pounds, lure them into a test room, hit them with a truncheon, color randomly assigned of course, and snap the photo. In fact the truncheon-hitting and photo-snapping would be done by an assistant who hadn't been told about the hypothesis, so he couldn't look expectant, hit harder, or snap the photo at just the right time.

Blondlot had destroyed his reputation with the sort of mistake that would get a failing grade and probably derisive laughter from the T.A. in a first-year undergraduate course on experimental design... in 1991.

But this had been a bit longer ago, in 1904, and so it had taken months before Robert Wood had formulated the obvious alternative hypothesis and figured out how to test it, and dozens of other scientists had been sucked in.

More than two centuries after science had gotten started. That late in scientific history, it still hadn't been obvious.

Which made it entirely plausible that in the tiny wizarding world, where science didn't seem much known at all, no one had ever tried the first, the simplest, the most obvious thing that any modern scientist would think to check.

The books were full of complicated instructions for all the things you had to do exactly right in order to cast a spell. And, Harry had hypothesized, the process of obeying those instructions, of checking that you were following them correctly, probably did do something. It forced you to concentrate on the spell. Being told to just wave your wand and wish probably wouldn't work as well. And once you believed the spell was supposed to work a certain way, once you had practiced it that way, you might not be able to convince yourself that it could work any other way...

...if you did the simple but wrong thing, and tried to test alternative forms yourself.

But what if you didn't know what the original spell had been like?

What if you gave Hermione a list of spells she hadn't studied yet, taken from a book of silly prank spells in the Hogwarts library, and some of those spells had the correct and original instructions, while others had one changed gesture, one changed word? What if you kept the instructions constant, but told her that a spell supposed to create a red worm was supposed to create a blue worm instead?

Well, in that case, it had turned out...

...Harry was having trouble believing his results here...

...if you told Hermione to say 'Oogely boogely' with the vowel durations in the ratio of 3 to 1 to 1, instead of the correct ratio of 3 to 1 to 2, you still got the bat but it wouldn't glow any more.

Not that belief was irrelevant here. Not that only the words and wand movements mattered.