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" Neel cuts in: " Where'd you grow up?" " Palo Alto," she says. From there to Stanford to Google: for a girl obsessed with the outer limits of human potential, Kat has stayed pretty close to home. Neel nods knowingly. " The suburban mind cannot comprehend the emergent complexity of a New York sidewalk." " I don't know about that," Kat says, narrowing her eyes. " I'm pretty good with complexity." " See, I know what you're thinking," Neel says, shaking his head." You're thinking it's just an agent-based simulation, and everybody out here follows a pretty simple set of rules" -- Kat is nodding--" and if you can figure out those rules, you can model it. You can simulate the street, then the neighborhood, then the whole city. Right?" " Exactly. I mean, sure, I don't know what the rules are yet, but I could experiment and figure them out, and then it would be trivial--" " Wrong," Neel says, honking like a game-show buzzer. " You can't do it. Even if you know the rules-- and by the way, there are no rules--but even if there were, you can't model it. You know why?" My best friend and my girlfriend are sparring over simulations. I can only sit back and listen. Kat frowns. " Why?" " You don't have enough memory." " Oh, come on--" " Nope. You could never hold it all in memory. No computer's big enough. Not even your what's-it-called--" " The Big Box." " That's the one. It's not big enough. This box--" Neel stretches out his hands, encompasses the sidewalk, the park, the streets beyond--" is bigger." The snaking crowd surges forward. "
