Contact - Carl Sagan [181]
From the expression on his face, she was afraid she had not been clear. She made a small swerve in the monologue. "…but not to calculate the digits in a number like pi, print than out, and present them for inspection. There isn't enough time for that. Instead, the program races through the digits in pi and pauses even to think about it only when there's some anomalous sequence of zeros and ones. You know what I'm saying? Something nonrandom. By chance, there'll be some zeros and ones, of course. Ten percent of the digits will be zeros, and another ten percent will be ones. On average. The more digits we race through, the longer the sequences of pure zeros and ones that we should get by accident. The program knows what's expected statistically and only pays attention to unexpectedly long sequences of zeros and ones. And it doesn't only look in base ten."
"I don't understand. If you look at enough random numbers, won't you get any pattern you want simply by chance?"
"Sure. But you can calculate how likely that is. If you get a very complex message very early on, you know it can't be by chance. So, every day in the early hours of the morning the computer works on this problem. No data from the outside world goes in. And so far no data from the inside world comes out. It just runs through the optimum series expansion for pi and watches the digits fly. It minds its own business. Unless it finds something, it doesn't speak unless it's spoken to. It's sort of contemplating its navel."
"I'm no mathematician, God knows. But could you give me a f'r instance?"
"Sure." She searched in the pockets of her jump suit for a piece of paper and could find none. She thought about reaching into his inside breast pocket, retrieving the envelope she had just given him and writing on it, but decided that was too risky out here in the open. After a moment, he understood and produced a small spiral notebook.
"Thanks. Pi starts out 3.1415926…You can see that the digits vary pretty randomly. Okay, a one appears twice in the first four digits, but after you keep on going for a while it averages out. Each digit-0, 1, 2, 3, 4, 5, 6, 7, 8, 9-appears almost exactly ten percent of the time when you've accumulated enough digits. Occasionally you'll get a few consecutive digits that are the same-4444, for example- but not more than you'd expect statistically. Now, suppose you're running merrily through these digits and suddenly you find nothing but fours. Hundreds of fours all in a row. That couldn't carry any information, but it also couldn't be a statistical fluke. You could calculate the digits in pi for the age of the universe and, if the digits are random, you'd never go deep enough to get a hundred consecutive fours."
"It's like the search you did for the Message. With these radio telescopes."
"Yes; in both cases we were looking for a signal that's well out of the noise, something that can't be just a statistical fluke."
"But it doesn't have to be a hundred fours-is that right? It could speak to us?"
"Sure. Imagine after a while we get a long sequence of just zeros and ones. Then, just as we did with the Message, we could pull a picture out, if there's one in there. You understand, it could be anything."
"You mean you could decode a picture hiding in pi and it would be a mess of Hebrew letters?"
"Sure. Big blade letters, carved in stone." He looked at her quizzically.
"Forgive me, Eleanor, but don't you think you're being a mite too…indirect? You don't belong to a silent order of Buddhist nuns. Why don't you just tell your story?"
"Palmer, if I had hard evidence, I'd speak up. But if I don't have any, people like Kitz will say that I'm lying. Or hallucinating.