Emergence 2009: Langton's Ant I

One ant has a characteristic behavior: unordered motion that eventually switches to road-building. It appears as if the ant learns a new behavior and wants to continue that new behavior, even if it is momentarily blocked.

Two ants, both beginning at the origin and headed in opposite directions, exhibit the same combination of unordered motion and road-building. They begin by trying to act independently of one another. However, they soon interfere with one another and appear to argue before teaming up to reverse their actions and begin again in a different orientations. Between the two of them, they change their minds, repair their mistakes and try something new. They appear to communicate with one another.

Four ants take it to a whole new level. Not only do they communicate with one another, they synchronize their actions and break out of the road-building behavior they'd exhibit on their own. They can even communicate across a distance, as in the case of Step 4 when they all begin the specified number of patches from the origin headed in different directions, and still display highly symmetric repeating patterns.

What has changed in these four setups? Do the ants actually learn, communicate, argue, or synchronize of their own will? No. Other than the color and heading of each additional ant, none of the rules have changed. The ants still move forward, change a black patch to their own color and turn right, or turn a non-black patch to black and turn left. With the addition of multiple ants, behavior is observed that does not appear in only one ant. This is an example of emergent behavior: simple interactions of simple things that yeild surprisingly complex outcomes.