watch already, good - so that the future you can pass. It's all there in the pamphlet."
"Ahahahaa. And what happens when someone ignores that advice?"
Professor McGonagall pursed her lips. "I understand that it can be quite disconcerting."
"And it doesn't, say, create a paradox that destroys the universe."
She smiled tolerantly. "Mr. Potter, I think I'd remember hearing if that had ever happened."
"THAT IS NOT REASSURING! HAVEN'T YOU PEOPLE EVER HEARD OF THE ANTHROPIC PRINCIPLE? AND WHAT IDIOT EVER BUILT ONE OF THESE THINGS FOR THE FIRST TIME?"
Professor McGonagall actually laughed. It was a pleasant, glad sound that seemed surprisingly out of place on that stern face. "You're having another 'you turned into a cat' moment, aren't you, Mr. Potter. You probably don't want to hear this, but it's quite endearingly cute."
"Turning into a cat doesn't even BEGIN to compare to this. You know right up until this moment I had this awful suppressed thought somewhere in the back of my mind that the only remaining answer was that my whole universe was a computer simulation like in the book Simulacron 3 but now even that is ruled out because this little toy ISN'T TURING COMPUTABLE! A Turing machine could simulate going back into a defined moment of the past and computing a different future from there, an oracle machine could rely on the halting behavior of lower- order machines, but what you're saying is that reality somehow self-consistently computes in one sweep using information that hasn't... happened... yet..."
Realisation struck Harry a pile-driver blow.
It all made sense now. It all finally made sense.
"SO THAT'S HOW THE COMED-TEA WORKS! Of course! The spell doesn't force funny events to happen, it just makes you feel an impulse to drink right before funny things are going to happen anyway! I'm such a fool, I should have realised when I felt the impulse to drink the Comed-Tea before Dumbledore's second speech, didn't drink it, and then choked on my own saliva instead - drinking the Comed-Tea doesn't cause the comedy, the comedy causes you to drink the Comed-Tea! I saw the two events were correlated and assumed the Comed-Tea had to be the cause and the comedy had to be the effect because I thought temporal order restrained causation and causal graphs had to be acyclic BUT IT ALL MAKES SENSE ONCE YOU DRAW THE CAUSAL ARROWS GOING BACKWARDS IN TIME!"
Realisation struck Harry the second pile-driver.
This one he managed to keep quiet, making only a small strangling sound like a dying kitten as he realised who'd put the note on his bed this morning.
Professor McGonagall's eyes were alight. "After you graduate, or possibly even before, you really must teach some of these Muggle theories at Hogwarts, Mr. Potter. They sound quite fascinating, even if they're all wrong."
"Glehhahhh..."
Professor McGonagall offered him a few more pleasantries, demanded a few more promises to which Harry nodded, said something about not talking to snakes where anyone could hear him, reminded him to read the pamphlet, and then somehow Harry found himself standing outside her office with the door closed firmly behind him.
"Gaahhhrrrraa..." Harry said.
Why yes his mind was blown.
Not least by the fact that, if not for the Prank, he might well have never obtained a Time-Turner in the first place.
Or would Professor McGonagall have given it to him anyway, only later in the day, whenever he got around to asking about his sleep disorder or telling her about the Sorting Hat's message? And would he, at that time, have wanted to pull a prank on himself which would have led to him getting the Time-Turner earlier? So that the only self-consistent possibility was the one in which the Prank started before he even woke up in the morning...?
Harry found himself considering, for the first time in his life, that the answer to his question might be literally inconceivable. That since his own brain contained neurons that only ran forwards in time, there was nothing his brain could do, no operation it could perform, which was conjugate to the operation of a Time Turner.
Up until this point Harry had lived by the admonition of E. T. Jaynes that if you were ignorant about a phenomenon, that was a fact about your own state of mind, not a fact about the phenomenon itself; that your uncertainty was a fact about you, not a fact about whatever you were uncertain about; that ignorance existed in the mind, not in reality; that a blank map did not correspond to a blank territory. There were mysterious questions, but a mysterious answer was a contradiction in terms. A phenomenon could be mysterious to some particular person, but there could be no phenomena mysterious of themselves. To worship a sacred mystery was just to worship your own ignorance.
So Harry had looked upon magic and refused to be intimidated. People had no sense of history, they learned about chemistry and biology and astronomy and thought that these matters had always been the proper meat of science, that they had never been mysterious. The stars had once been mysteries. Lord Kelvin had once called the nature of life and biology - the response of muscles to human will and the generation of trees from seeds - a mystery "infinitely beyond" the reach of science. (Not just a little beyond, mind you, but infinitely beyond. Lord Kelvin certainly had felt a huge emotional charge from not knowing something.) Every mystery ever solved had been a puzzle from the dawn of the human species right up until someone solved it.
Now, for the first time, he was up against the prospect of a mystery that was threatening to be permanent. If Time didn't work by acyclic causal networks then Harry didn't understand what was meant by cause and effect; and if Harry didn't understand causes and effects then he didn't understand what sort of stuff reality might be made of instead; and it was entirely possible that his human mind never could understand, because his brain was made of old-fashioned linear-time neurons, and this had turned out to be an impoverished subset of reality.
