Professor McGonagall seemed highly amused. “Would you like a further demonstration, Mr. Potter?”
“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?”
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. Three thousand years, more or less, that was how long humanity had been investigating the natural world. In the beginning the ancient Greeks had thought that there were different rules in different places, a law for the heavens and a different law for the Earth. For hundreds of years the march of Reason had progressed steadily away from that starting point. Humanity had descended beneath the surface of the world, finding tissues beneath bodies, cells beneath tissues, chemistry beneath cells, quarks beneath atoms. The simple things, the eternally stable and unvarying things, the things of pure causality and math, beneath the world of surface appearances forever in flux. The laws of gravity that Newton had laid down, that seemed in retrospect to have governed every piece of the solar system since forever; and even when the orbital precession of Mercury had been discovered, an exception to Newton’s laws, Einstein had come along and discovered the new theory, the new universal, the new rule that was revealed to have always governed since the beginning. The true rules were the same everywhere and every when for every part of the universe, you didn’t have special cases for different surface appearances and exceptions whenever it was convenient, that was what humanity had learned over the last three thousand years, not to mention that the mind was the brain and the brain was made of neurons and if you damaged the brain the mind lost the corresponding ability, destroy the hippocampus and the person lost the ability to form new memories, a brain was what a person was—
And then a woman turned into a cat, so much for all that.
I'm loving it. If you haven't already read Harry Potter and the Methods of Rationality (or have read it, but haven't checked back recently for updates), and enjoyed the original Harry Potter books, give it a try!