Harry Potter Learns Science

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My favorite fanfic these days is Harry Potter and the Methods of Rationality. It’s insightful, funny, and teaches you real science. And it’s written by the guy who started my favorite rationality wiki, Less Wrong.

In it, Harry is raised by an Oxford professor, and applies the scientific method to magic. He’s also a chessmaster — someone who can read people and plan deeply. And his enemies are similarly improved.

Here’s an excerpt from chapter 2, after McGonagall demonstrates levitation to prove that magic is real:


“You don’t have to,” Harry said. “We’ve performed a definitive experiment. But…” Harry hesitated. He couldn’t help himself. Actually, under the circumstances, he shouldn’t be helping himself. It was right and proper to be curious. “What else can you do?”

Professor McGonagall turned into a cat.

Harry scrambled back unthinkingly, backpedaling so fast that he tripped over a stray stack of books and landed hard on his bottom with a thwack. His hands came down to catch himself without quite reaching properly, and there was a warning twinge in his shoulder as the weight came down unbraced.

At once the small tabby cat morphed back up into a robed woman. “I’m sorry, Mr. Potter,” McGonagall said, sounding sincere, though her lips were twitching toward a smile. “I should have warned you.”

Harry was breathing in short pants. His voice came out choked. “You can’t DO that!”

“It’s only a Transfiguration,” said McGonagall. “An Animagus transformation, to be exact.”

“You turned into a cat! A SMALL cat! You violated Conservation of Energy! That’s not just an arbitrary rule, it’s implied by the form of the quantum Hamiltonian! Rejecting it destroys unitarity and then you get FTL signaling! And cats are COMPLICATED! A human mind can’t just visualize a whole cat’s anatomy and, and all the cat biochemistry, and what about the neurology? How can you go on thinking using a cat-sized brain?”

McGonagall’s lips were twitching harder now. “Magic.”

“Magic isn’t enough to do that! You’d have to be a god!”

McGonagall blinked. “That’s the first time I’ve ever been called that.”

A blur was coming over Harry’s vision, as his brain started to comprehend what had just broken. The whole idea of a unified universe with mathematically regular laws, that was what had been flushed down the toilet; the whole notion of physics. Three thousand years of resolving big complicated things into smaller pieces, discovering that the music of the planets was the same tune as a falling apple, finding that the true laws were perfectly universal and had no exceptions anywhere and took the form of simple math governing the smallest parts, not to mention that the mind was the brain and the brain was made of neurons, a brain was what a person was –

And then a woman turned into a cat, so much for all that.


The writing is generally book-level quality, substantially better than most fanfics. There is one false note — it’s chapter 52, and you’ll know what I mean when you get there — but on the whole, the story is character driven, intelligent, and plays fair.

The author isn’t a mage. But if he were, he’d be a good one.

Check out Harry Potter and the Methods of Rationality here.

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