Harry Potter and the Methods of Rationality

That sort of thing did sometimes take longer than two months. Muggle science hadn't gone to the moon in the first week after Galileo.

But Harry still couldn't stop the huge smile that was stretching his cheeks so wide they were starting to hurt.

Harry had always been frightened of ending up as one of those child prodigies that never amounted to anything and spent the rest of their lives boasting about how far ahead they'd been at age ten. But then most adult geniuses never amounted to anything either. There were probably a thousand people as intelligent as Einstein for every actual Einstein in history. Because those other geniuses hadn't gotten their hands on the one thing you absolutely needed to achieve greatness. They'd never found an important problem.

You're mine now, Harry thought at the walls of Diagon Alley, and all the shops and items, and all the shopkeepers and customers; and all the lands and people of wizarding Britain, and all the wider wizarding world; and the entire greater universe of which Muggle scientists understood so much less than they believed. I, Harry James Potter-Evans-Verres, do now claim this territory in the name of Science.

Lightning and thunder completely failed to flash and boom in the cloudless skies.

"What are you smiling about?" inquired Professor McGonagall, warily and wearily.

"I'm wondering if there's a spell to make lightning flash in the background whenever I make an ominous resolution," explained Harry. He was carefully memorising the exact words of his ominous resolution so that future history books would get it right.

"I have the distinct feeling that I ought to be doing something about this," sighed Professor McGonagall.

"Ignore it, it'll go away. Ooh, shiny!" Harry put his thoughts of world conquest temporarily on hold and skipped over to a shop with an open display, and Professor McGonagall followed.

Harry had now bought his potions ingredients and cauldron, and, oh, a few more things. Items that seemed like good things to carry in Harry's Bag of Holding (aka Moke Super Pouch QX31 with Undetectable Extension Charm, Retrieval Charm, and Widening Lip). Smart, sensible purchases.

Harry genuinely didn't understand why Professor McGonagall was looking so suspicious.

Right now, Harry was in a shop expensive enough to display in the twisting main street of Diagon Alley. The shop had an open front with merchandise laid out on slanted wooden rows, guarded only by slight grey glows and a young-looking salesgirl in a much-shortened version of witch's robes that exposed her knees and elbows.

Harry was examining the wizarding equivalent of a first-aid kit, the Emergency Healing Pack Plus. There were two self-tightening tourniquets. A syringe of what looked like liquid fire, which was supposed to drastically slow circulation in a treated area while maintaining oxygenation of the blood for up to three minutes, if you needed to prevent a poison from spreading through the body. White cloth that could be wrapped over a part of the body to temporarily numb pain. Plus any number of other items that Harry totally failed to comprehend, like the "Dementor Exposure Treatment", which looked and smelled like ordinary chocolate. Or the "Bafflesnaffle Counter", which looked like a small quivering egg and carried a placard showing how to jam it up someone's nostril.

"A definite buy at five Galleons, wouldn't you agree?" Harry said to Professor McGonagall, and the teenage salesgirl hovering nearby nodded eagerly.

Harry had expected the Professor to make some sort of approving remark about his prudence and preparedness.

What he was getting instead could only be described as the Evil Eye.

"And just why," Professor McGonagall said with heavy scepticism, "do you expect to need a healer's kit, young man?" (After the unfortunate incident at the Potions shop, Professor McGonagall was trying to avoid saying "Mr. Potter" while anyone else was nearby.)

Harry's mouth opened and closed. "I don't expect to need it! It's just in case!"

"Just in case of what?"

Harry's eyes widened. "You think I'm planning to do something dangerous and that's why I want a medical kit?"

A look of grim suspicion and ironic disbelief was the answer.

"Great Scott!" said Harry. (This was an expression he'd learned from the mad scientist Doc Brown in Back to the Future.) "Were you also thinking that when I bought the Feather-Falling Potion, the Gillyweed, and the bottle of Food and Water Pills?"

"Yes."

Harry shook his head in amazement. "Just what sort of plan do you think I have going, here?"

"I don't know," Professor McGonagall said darkly, "but it ends either in you delivering a ton of silver to Gringotts, or in world domination."

"World domination is such an ugly phrase. I prefer to call it world optimisation."

This hilarious joke failed to reassure the witch giving him the Look of Doom.

"Wow," Harry said, as he realised that she was serious. "You really think that. You really think I'm planning to do something dangerous."

"Yes."

"Like that's the only reason anyone would ever buy a first-aid kit? Don't take this the wrong way, Professor McGonagall, but what sort of crazy children are you used to dealing with?"

"Gryffindors," spat Professor McGonagall, the word carrying a freight of bitterness and despair that fell like an eternal curse on all youthful enthusiasm and high spirits.

"Deputy Headmistress Professor Minerva McGonagall," Harry said, putting his hands sternly on his hips. "I am