What It Predicts

The machine found it on a Tuesday and printed it on one sheet of paper, like a telegram. Mulloy read it aloud. It was a polynomial, eleven terms, and the coefficients looked like a phone number.

“It fits,” he said.

That was all he said for a while. Then he said, “It fits everything.”

We had fed it the sky. The whole of it we could measure: the supernovae, the redshifts, a billion galaxies running away from us since the start. Down to the last decimal.

That was the job. For twenty years the trade had been stuck on one question. Why does the expansion speed up? Something out there, pushing. We called it dark energy, which is a gentleman’s way of saying we didn’t know what it was.

Mulloy got the idea of giving the problem to the machine in the basement. Two racks, a fan, a card reader. Symbolic regression, the company man calls it. It tries equations the way a safecracker works a lock, and it has all night. We had nothing better to do, and neither did it.

It hunted for eleven months. It tried more equations than there are atoms in the visible universe; that was the company man’s figure, and he was paid to say things like that.

Then it stopped hunting and printed its answer. One line. A polynomial.

We checked it. Every point in fourteen billion years of expansion, every one of our measurements, every one of our errors. The curve went through all of them like a needle through cloth.

No dark energy. No physics in it at all, as far as we could see. Just a curve through dots, and every dot landed on it.

That was what scared us. Data never fits like that. The universe is sloppy, and so are our instruments. A curve that goes through every point means somebody tuned it.

Nobody tuned it. The machine found it.

We ran the machine on other problems. It behaved. We fed it the data shuffled; it returned the same polynomial. We fed it half the data; it returned the same polynomial, and the half it had never seen fit it too. Mulloy took a week off and came back gray. Nothing wrong with the data, he said. Nothing wrong with the machine. Nothing wrong with the polynomial. It was as true as arithmetic, and it meant nothing.

We argued about it for months. It went the rounds of the journals, unsigned. Nobody could break it, and nobody wanted to claim it.

Susie is seven. She comes with me on Saturdays when her mother works, because the lab has a window and a coffee machine, in that order. She likes the window. She can see the whole sky from it.

She stood on a chair in front of the board and read the polynomial like a phone number. Then she said, “What does it predict?”

“It doesn’t predict,” Mulloy said. “It describes. It describes everything.”

“Everything does something,” Susie said. “What does it do?”

We had never asked it that. We had asked if it was true. We had asked if it meant anything. Nobody had asked what it did.

“It does the expansion,” I said. “It is the expansion. It tells you where every galaxy was and is and will be.”

“Will be,” she said. “That’s predicting.”

“Well. It runs forward. It goes on expanding, slower and slower, and it never quite stops.”

“Then what does it predict about the machine?”

The question sat in the room.

“Nothing,” Mulloy said. “It has nothing to do with the machine.”

“Everything has something to do with everything,” Susie said. “You told me.”

I walked to the board. I did what I should have done the day the paper came out of the machine. I evaluated the polynomial at the date and hour the machine began its run.

I wrote down the answer.

It was the machine’s serial number.

Mulloy went gray. I went gray. Susie stayed the color she was.

Then I decoded the rest. The coefficients, read as digits, were the machine. Its memory. Its logic, folded over and over until it was small enough to sit inside a formula. It was all there, even the Tuesday it started. The machine had not found the equation of the universe.

It had found the equation of the machine.

“But it fits the sky,” Mulloy said. “It fits the sky.”

It fits because the machine is in the sky. The universe’s history contains the machine. The polynomial describes everything in that history, and the machine is part of that history. It read everything there was, and everything there was included itself.

We’d been reading ourselves and calling it the universe.

I turned to the board and wrote the serial number again, slowly, under the polynomial.

“It predicts that it exists,” I said. “That’s all it ever predicted. It exists, and it found itself, and it will go on finding itself. Forever.”

“Huh,” Susie said. She looked at the board a long time, the way she watched the sky from the window. “Then it never gets an answer. It just gets itself.”

“Never,” I said.

“That’s the longest game of solitaire I ever heard of,” she said. “Can we go home now?”