Wizardry Violates the Conservation of Energy

“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 catsized 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.

When rational Harry Potter sees a woman turn into a cat, he cannot believe the violation of the laws of physics.