There’s been a fair amount of discussion on this blog lately about whether people can choose their beliefs or whether beliefs are compelled by evidence (and then some more about what this all means for free will). Good news for me, because that was all the excuse I needed to post the following excerpt from Harry Potter and the Methods of Rationality, a fanfiction story written by AI research Eliezer Yudkowsky.
In Yudkowsky’s story, Harry was raised by a science professor instead of the Dursleys. Some parts of the story are fairly didactic (not that I mind), but the plots that Yudowsky has invented are intricate and entertaining. Since his Harry has more resources at his disposal, he’s made Voldemort proportionately smarter — much better than the poor planner with silly goals that Harry ended up facing in canon.
The scene below occurs after Harry Potter and Draco Malfoy have finished examining evidence about why wizarding blood is getting weaker over time. They were both studying the scientific method together, since Malfoy believed it was giving Harry advantages even in the wizarding world. Malfoy believes any weakening of magic is the result of intermarriage with muggles (non-wizards), but it turns out that the evidence he gathered proves his theory false. In the passage below, Yudowsky adapts Carl Sagan’s Invisible Dragon story and shows us what happens when you try to willfully change your beliefs.
“Fine. Then you and I are through. I’m going to just walk away and forget any of this ever happened.”
“Draco… you can’t forget. Don’t you understand? That was your sacrifice.”
Draco stopped in midstride and turned around. “What are you talking about?”
“To become a scientist. You questioned one of your beliefs, not just a small belief but something that had great significance to you. You did experiments, gathered data, and the outcome proved the belief was wrong. You saw the results and understood what they meant.” Harry Potter’s voice was faltering. “Remember, Draco, you can’t sacrifice a true belief that way, because the experiments will confirm it instead of falsifying it. Your sacrifice to become a scientist was your false belief that wizard blood was mixing and getting weaker.”
“That’s not true!” said Draco. “I didn’t sacrifice the belief. I still believe that!” His voice was getting louder, and the chill was getting worse.
Harry Potter shook his head. His voice came in a whisper. “Draco… I’m sorry, Draco, you don’t believe it, not anymore.” Harry’s voice rose again. “I’ll prove it to you. Imagine that someone tells you they’re keeping a dragon in their house. You tell them you want to see it. They say it’s an invisible dragon. You say fine, you’ll listen to it move. They say it’s an inaudible dragon. You say you’ll throw some cooking flour into the air and see the outline of the dragon. They say the dragon is permeable to flour. And the telling thing is that they know, in advance, exactly which experimental results they’ll have to explain away. They know everything will come out the way it does if there’s no dragon, they know in advance just which excuses they’ll have to make. So maybe they say there’s a dragon. Maybe they believe they believe there’s a dragon, it’s called belief-in-belief. But they don’t actually believe it. You can be mistaken about what you believe, most people never realize there’s a difference between believing something and thinking it’s good to believe it.” Harry Potter had risen from the desk now, and taken a few steps toward Draco. “And Draco, you don’t believe any more in blood purism, I’ll show you that you don’t. If blood purism is true, then Hermione Granger doesn’t make sense, so what could explain her? Maybe she’s a wizarding orphan raised by Muggles, just like I was? I could go to Granger and ask to see pictures of her parents, to see if she looks like them. Would you expect her to look different? Should we go perform that test?”“They would have put her with relatives,” Draco said, his voice trembling. “They’ll still look the same.”
“You see. You already know what experimental result you’ll have to excuse. If you still believed in blood purism you would say, sure, let’s go take a look, I bet she won’t look like her parents, she’s too powerful to be a real Muggleborn -”
“They would have put her with relatives!”
“Scientists can do tests to check for sure if someone is the true child of a father. Granger would probably do it if I paid her family enough. She wouldn’t be afraid of the results. So what do you expect that test to show? Tell me to run it and we will. But you already know what the test will say. You’ll always know. You won’t ever be able to forget. You might wish you believed in blood purism, but you’ll always expect to see happen just exactly what would happen if there was only one thing that made you a wizard. That was your sacrifice to become a scientist.”
Draco’s breathing was ragged. “Do you realize what you’ve done?” Draco surged forward and he seized Harry by the collar of his robes. His voice rose to a scream, it sounded unbearably loud in the closed classroom and the silence. “Do you realize what you’ve done?”
Harry’s voice was shaky. “You had a belief. The belief was false. I helped you see that. What’s true is already so, owning up to it doesn’t make it worse -”
The fingers on Draco’s right hand clenched into a fist and that hand dropped down and blasted up unstoppably and punched Harry Potter in the jaw so hard that his body went crashing back into a desk and then to the floor.
The whole story can be read here at fanfiction.net.