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Harry Potter Ends (Again)

Adam Chalmers rationalises fanfiction that made him think.

Illustration by Monica Renn.

“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 signalling! And cats are COMPLICATED! A human mind can’t just visualise 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?” Professor McGonagall’s lips were twitching harder now. “Magic.”

After five years and 640,000 words, Harry Potter and the Methods of Rationality was finally finished last week. In Eliezer Yudkowsky’s fan fiction, Harry Potter is a child prodigy who read the Feynman Lectures on Physics at age 10, and uses his superintelligence to battle a similarly intelligent Voldemort.

It’s often said that J.K. Rowling’s greatest strength wasn’t her writing, but her worldbuilding. Methods of Rationality’s best moments come when its hyperintelligent characters find inventive uses for the magical elements of Rowling’s world. I loved reading Harry consider transmuting a pebble into antimatter, which would create an explosion big enough to level England. Or listening to Voldemort explain how he hid his horcruxes in actually safe places by dropping them into the Marianas Trench or sneaking them onto deep space probes. There’s even a scheme to arbitrage gold between Wizarding and Muggle Britain. If you’ve ever found yourself wondering exactly how Time Turners work, or why no-one used the Philosopher’s Stone to cure cancer, you’ll enjoy reading this.

Eliezer Yudkowsky is better known for his research in the nonprofit Machine Intelligence Research Institution, and his blogging about rationality and psychology at Overcoming Bias and Less Wrong. Yudkowsky began writing his “rationalist fan fiction” with the goal of both entertaining readers and teaching valuable lessons about human and machine intelligence. Readers learn alongside the Hogwarts students as Harry and Hermione discuss the base rate fallacy, risk aversion, scope insensitivity and other biases. Sometimes the story will unapologetically become a cognitive psychology textbook for a chapter. But generally, it manages to explain science in an accessible Carl Sagan or Neil deGrasse Tyson manner. The readers’ new rationality skills even affected the story’s final outcome. Chapter 113 sees a defenseless Harry surrounded by Voldemort’s forces, and ended with a note from the author: if the readers could figure out a viable plan for Harry to destroy Voldemort, he would incorporate this plan into the text and post the story’s final ten chapters. Otherwise there would be a “shorter and sadder” ending instead.

The final chapter was followed by a thank you from the author, along with a self-described “shameless” request to nominate it for a Hugo award, and to be put in contact with J.K. Rowling if any readers personally knew her. The ending was celebrated with wrap parties in twenty cities around the world. Yudkowsky is currently brainstorming a new original story, and encourages readers to either research with or donate to his Machine Intelligence Research Institute.

Adding hyperintelligent, genre-savvy characters into someone else’s fictional world can break both a story and the rules of writing. It’s also incredibly fun. Methods of Rationality has spawned a series of similar ‘rationalist’ fan fiction. Is fighting small scale crime really the best way for Superman to help Earth? Can Pokemon be combined with modern day evolutionary theory? If you’ve ever overthought your favorite TV show, or come up with a convoluted fan theory to rescue a movie from plot holes, you might enjoy rationalist fan fiction.