Emergence by Steven Johnson
Author:Steven Johnson
Language: eng
Format: epub
Publisher: Scribner
5
Control Artist
On the screen, the pixels dance: bright red dots with faint trails of green, scurrying across a black background, like fireflies set against the sky of a summer night. For a few seconds, the movement on-screen looks utterly random: pixels darting back and forth, colliding, and moving on. And then suddenly a small pocket of red dots gather together in a pulsing, erratic circle, ringed by a strip of green. The circle grows as more red pixels collide with it; the green belt expands. Seconds later, another lopsided circle appears in the corner of the screen, followed by three more. The circles are unlike any geometric shape youâve ever seen. They seem more like a life-formâa digital blobâpulsing haphazardly, swelling and contracting. Two blobs slowly creep toward each other, then merge, forming a single unit. After a few minutes, seven large blobs dominate, with only a few remaining free-floating red pixels ambling across the screen.
Welcome to the world of Mitch Resnickâs tool for visualizing self-organizing systems, StarLogo. A descendant of Seymour Papertâs legendary turtle-based programming language, Logo, StarLogo allows you to model emergent behavior using simple, English-like commandsâand it displays that behavior in vivid, real-time animations. If decentralized systems can sometimes seem counterintuitive or abstract, difficult to describe in words, StarLogo makes them come to life with dynamic graphics that are uniquely suited for the Nintendo generation. If a calendar is a tool for helping us think about the flow of time, and a pie chart is a tool for thinking about statistical distributions, StarLogo is a tool for thinking about bottom-up systems. And, in fact, those lifelike blobs on the screen take us back to the very beginnings of our story: they are digital slime molds, cells aggregating into larger clusters without any âpacemakerâ cell leading the way.
âThose red pixels are the individual slime mold cells,â Resnick says, pointing at the screen, sitting in his Cambridge office. âTheyâre programmed to wander aimlessly around the screen space, and as they wander, they âemitâ the green color, which quickly fades away. That color is the equivalent of the c-AMP chemical that the molds use to coordinate their behavior. Iâve programmed the red cells to âsniffâ the green color and follow the gradient in the color. âSmellingâ the green pixels leads the cells toward each other.â
Like Gordonâs ant colonies, Resnickâs slime mold simulation is sensitive to population density. âLetâs start with only a hundred slime mold cells,â he says, adjusting a slider on the screen that alters the number of cells in the simulation. He presses a start button, and a hundred red pixels begin their frenetic danceâonly this time, no clusters appear. There are momentary flashes of green as a few cells collide, but no larger shapes emerge at all.
âWith a hundred cells, there isnât enough contact for the aggregates to form. But triple the population like so,â he says, pulling the slider farther to the right, âand you increase the contact between cells. At three hundred cells, youâll usually get one cluster after a few minutes, and sometimes two.
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