WWW 2: Watch (33 page)

“There were fourteen entries,” her mother said. “And, to Axelrod’s surprise, the simplest entry—it required just five lines of computer code—won. It was called Tit for Tat, and it had been submitted by Anatol Rapoport, who, as it happens, was at the University of Toronto. Tit for Tat took a very simple approach: start with cooperation, then do whatever the other player did on the previous move. To put it another way, Tit for Tat starts off as a peaceful dove, and only becomes a hawk if you become one first. But as soon as you stop defecting, it goes back to cooperating—it’s a peacemaker, see?”

“Cool,” said Caitlin, taking another bite.

“Axelrod spent a lot of time trying to figure out why Tit for Tat beat everything else. He decided it was because of its combination of being nice, retaliatory, forgiving, and clear. By nice, he meant it was never the first to defect. And its retaliation—defecting back if you defected against it—discouraged the other side from continuing to defect after trying it once. Its forgiveness helped restore mutual cooperation—it didn’t hold a grudge; as soon as you went back to cooperating, it went back to cooperating, too. And by clarity, Axelrod meant Tit for Tat’s strategy was easily understandable by the other player.”

Caitlin thought about all that—a fair bit of complexity, and even the appearance of advanced, reasoned, ethical behavior—emerging from something so simple. It reminded her of—

Of course!

It reminded her of cellular automata, of the processes she could see in the background of the World Wide Web that had apparently given rise to Webmind: a simple rule or set of rules that caused packets in the background to flip back and forth between two states, generating complex patterns. Could an endlessly iterating prisoner’s dilemma, or some other game-theoretical problem, be the rule underlying Webmind’s consciousness? That’d be cool.

But something else was puzzling her, too. “Why’s it called Tit for Tat? What do tits have to do with it?”

Her mother tried to suppress a grin. “It’s an old phrase, and it’s been distorted over the years. It used to be
tip for tap
—and both ‘tip’ and ‘tap’ mean to strike lightly and sharply.”

“Oh.” Not nearly as interesting. “You called Tit for Tat a peacemaker—but isn’t tipping and tapping really all about getting even?”

“Well, that’s one way of looking at it; it
is
retaliatory.”

“And, um, you said that this has something to do with Jesus. Getting even is
so
Old Testament. The New Testament has Jesus saying—um, something about not doing that.”

Caitlin’s mother astonished her by quoting scripture—accurately, she presumed; it was something she’d never heard her do before. “ ‘Ye have heard that it hath been said, An eye for an eye, and a tooth for a tooth: But I say unto you, That ye resist not evil: but whosoever shall smite thee on thy right cheek, turn to him the other also.’ ”

“Um,” said Caitlin. “Yeah. Like that.” She paused. “So, what’s the game-theoretical strategy for
that? ”

“That’s what we call Always Cooperate—or AllC, for short, “All” and the letter
C:
you cooperate no matter what the other person does. Except . . .”

“Yes?”

“Well, there’s more to it than that. The next verses say, ‘And if any man will sue thee at the law, and take away thy coat, let him have thy cloak also. And whosoever shall compel thee to go a mile, go with him twain.’ ‘Twain’ means ‘two’—that’s where the phrase ‘go the extra mile’ comes from. So, it’s all about not just giving them what they want, but giving them more than they asked for. I don’t know, call it DoubleAllC, or something like that.”

“But . . . hmmm.” Caitlin frowned. “I mean, you can’t play DoubleAllC very long—you’ll run out of stuff.” But then she got it. “Ah, but that’s the Christian thing, right? The reward isn’t in this life, it’s in the next one.”

“For a lot of Christians, yes.”

“But, um, if you don’t believe Christ is divine, Mom, do you believe in heaven?”

“No. When you die, you’re gone.”

“So does DoubleAllC, or even just plain old Always Cooperate, really make sense for a Unitarian—for someone who doesn’t believe there’s a reward to be had in an afterlife? I mean, DoubleAllC and AllC can’t win unless they’re playing against people using the same strategy. And you obviously
aren’t
—not in the scenario described: you’ve been struck on one cheek first, so you know you’re playing against someone who defects at least part of the time. In what game-theory way does turning the other cheek make sense? I mean, presumably the other guy is just going to hit you again.”

Her mother lifted her eyebrows. “Ah, but see, you’re missing something. The easiest games to model are two-person games, but real life is an
n
-person game: it involves a large and variable number of players. You might lose a lot to one person, but gain more than you expected from someone else. Person
A
might be cruel to you, but person
B,
seeing that, might be even more kind to you because of it. And when you’re playing with a lot of people, the game goes on indefinitely—and that makes a huge difference. The examples in the Old Testament couldn’t be endlessly iterated: an eye for an eye can only go two rounds—after that, you’re out of eyes. Even a tooth for a tooth ends after a maximum of thirty-two rounds.”

Caitlin took a sip of milk, and her mother went on. “That’s the problem with two-person iterated games: they eventually come to an end. Sometimes they end because, like with the dollar auction, players just give up because it’s become ridiculous. And sometimes they end because the players run out of time.

“In fact, there was a famous case of a game theorist being brought in to IBM to do some management-training exercises. He divided the managers into teams and had them play games in which cooperating was the best strategy—which was the point he wanted them to learn.

“Everything worked fine until just before 4:00 p.m., when the seminar was scheduled to end. Suddenly, one of the teams turned on the other and kept defecting. That team won, but the first team felt so betrayed, IBM had to send its members off for therapy, and it was months before they’d work at all with members of the other team again.”

“Wow,” said Caitlin.

“But if you take the whole of humanity as the field of players, then your interaction doesn’t end even if any one specific player drops out. That’s why reputation is so important, see? You’ve bought things on eBay, right? Well, that’s a perfect example: how you’ve treated other people shows up in your Feedback rating. The world knows if you defect. We’re all interconnected in a . . .”

“. . . a worldwide web?” said Caitlin.

She smiled. “Exactly.” She gobbled the last of her sandwich. “Speaking of which, we should get back upstairs . . .”

 

 

“All right,” said Tony Moretti, pacing down one side of the control room at WATCH. “Reports. Shel, you first.”

Shelton Halleck was leaning forward in his chair, his arms crossed in front of him on the workstation, the one with the snake tattoo on top. He was plainly exhausted. “We’ve been through everything Caitlin Decter has written with a fine-toothed comb,” he said. “And everything Malcolm and Barbara Decter and Kuroda have written, too, but there’s nothing about how Exponential actually works—nothing that contradicts what Decter told the CSIS agents, but nothing that confirms it, either.”

“All right,” said Tony. “Aiesha, what have you got?”

She looked more awake than Shel, but her voice was raw. “Maybe something, maybe nothing,” she said. “Caitlin set up a webcam chat with an Internet cartographer at the Technion a while ago: Anna Bloom is her name.” A dossier came up on the middle of the three big screens, showing a picture of an elderly gray-haired woman. “We weren’t monitoring Caitlin’s traffic back then, so we don’t have a recording of the video chat—but I can’t think of any reason for a girl in Canada to talk to a Web scientist in Israel
except
to discuss the structure of Exponential.”

“We could get the Mossad to speak to this Bloom,” said Tony. “The Technion is in Jerusalem?”

“No, Haifa,” Aiesha said. She turned and looked at the series of digital clocks on the back wall. “It’s almost 11:00 p.m. there.”

“There’s no time to waste,” Colonel Hume said. “Let me call her directly—one computer expert to another. It’s time to cut through all the bull.”

 

 

Caitlin’s instant messenger bleeped and the words
Mind-Over-Matter is now available
popped up. She felt her heart racing.

Hi,
she typed.

Hey!
Matt replied.
How was your day?

I’ve got the stuff from your locker,
he replied.
OK if I come by?

Caitlin was surprised to find her heart pounding. She paused, trying to think of something suitably witty or sexy to say, but then she mentally kicked herself for hesitating, because poor Matt must have been on tenterhooks.
Sure!
she wrote, and then, to take the sting out of her delay, she added a trio of smiley faces.

W00t!
he wrote.
’Bout half an hour, OK?

This time she replied immediately:
Yes.

Caitlin crossed the hall to speak to her mother, who was typing away with Webmind in her study.

“A friend’s coming over,” Caitlin said.

Her mother looked up from her keyboard. “Who is it?”

Caitlin found herself slightly embarrassed. “They were in my math class.”

But the pronoun obfuscation did not get past her mom. “It’s a boy,” she said at once.

“Um, yes.”

“Is it Trevor?”

“No! Don’t worry, Mom. He won’t be back.”

“Well, okay,” she said, and—

And there it was, that look she’d seen before: her mother trying to suppress a grin. “But, sweetheart,” she added, “you might want to clean yourself up a bit.”

Cripes!
She’d been so intent on Webmind that she hadn’t brushed her hair today, and she looked down now and saw that she was wearing just about the rattiest T-shirt she owned. And—
gak!
—she hadn’t showered for two days. She hurried down the hall to the bathroom.

 

 

 

 

The doorbell rang, and Caitlin found herself running to it. She was now wearing a silky blue shirt—one her mother said was too low-cut for school. But she was not going
to
school anymore; she was pleased with her impeccable logic. Her shoulder-length brown hair was still wet, but at least she’d brushed it.

She opened the door. “Hi, Matt!”

And—
wow!
—boy’s eyes really
did
do that. She’d read about it, but hadn’t yet seen it: straight to the boobs, and only apparently with an effort of will coming up to the face.

His voice cracked. It was
so
cute! “Hi, Caitlin!”

He had a—a sack, or something in his right hand. “Here’s your stuff,” he said, setting it down on the tiled floor.

“Thanks!”

In his left hand, he was holding something large and rectangular. He held it out.

“What’s that?” she asked.

“A card—everyone in math class signed it. They were all sorry to hear you’re leaving school.”

She took it. It was quite large, and clearly handmade: a big piece of Bristol board folded in half, with a color printout pasted to the front. She looked at the image. “Who’s that?”

He seemed surprised for a second, then: “Lisa Simpson.”

“Oh!” She’d never have guessed she looked like
that!
She opened the card. The caption, written in thick block letters, was easy to read: “Brainy Girls Rule!” And surrounding it were things, in various colors of ink, that must have been the students’ signatures, but she couldn’t read them; she had almost no visual experience with cursive writing. “Which one’s yours?”

He pointed.

“Do you do that on purpose?” she said. He’d printed his name in capitals, but the two Ts touched, looking like the letter
pi,
which she knew because it was also the Perimeter Institute’s logo.

“Not normally,” he said. “But I thought you’d like it.” There was an awkward silence for a moment, then: “Umm, would you like to go for a walk? Timmy’s isn’t that far . . .”

Her parents had forbidden her going out on her own while there might still be Federal agents waiting to abduct her, and she suspected they wouldn’t think Matt was buff enough to be a bodyguard; in fact, Caitlin thought she’d have no trouble taking him herself. “I can’t,” she said.

That same look Bashira had made: crestfallen. “Oh.” He took a half step backward, as if preparing to leave.

“But you can come in for bit,” Caitlin blurted out.

He smiled that lopsided smile of his.

Screw symmetry,
Caitlin thought, and she moved aside to let him enter.

They
could
head up to her bedroom, she supposed, but she’d never had a boy in her room in this house, and, besides, her mother was right across the hall and would hear everything they said.

Or they could stay on the ground floor, in the kitchen, or the living room, but—

No, just as with Bashira, the basement was the place to go: private, and no way her mother could hear.

She led the way down. The two black office chairs were side by side, tucked under the worktable. Matt took the one on the right, which meant he’d be on her blind side. This time she did speak up about it. “I can’t see out of my right eye, Matt.”

“Oh, um, actually, I know that.”

She was startled—but, well, it
was
public knowledge; video of the press conference was online, and there’d been a lot of news coverage about Dr. Kuroda’s miracle.

And then she had a sudden thought: he knew she couldn’t see him when he was on her right, and yet he’d chosen twice now to position himself there. Maybe he was self-conscious about his appearance; living in a world of Bashiras could do that to a person, Caitlin supposed.