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The World of Langton's Ant:
Thinking about "Purpose"

Part 1
Watching: What's It Do?

What do we mean when we say that something has a "purpose"? That something is acting with "purpose"? That we ourselves are acting "purposefully"? Langton's Ant was created by Chris Langton in the 1980's as a way of helping to think about such questions. Before saying exactly what it is, let's just watch Langton's ant behave for a while and see what it makes us think. Let's get to know the ant a bit before trying to explain it (that's always a good idea in science; see A Feeling for the Organism: The Life and Work of Barbara McClintock, by Evelyn Fox Keller).

Try it Out

To see Langton's ant, click on Set/Reset to the right. The ant will appear as a red triangle on a light background. Now click Start/stop and watch what happens. The ant is moving ... still moving .... STILL moving, right? And it doesn't seem to have much purpose, right? Its just sort of wandering around, aimlessly. But keep an eye on it for a bit more, until the counter gets to 10,000 or so. BINGO ... all of a sudden the ant seems to be going somewhere. To have acquired a "purpose" in life? To have decided to build a road?

Try It Again

What's going on? Why did the ant stop wandering aimlessly and start going somewhere? Would it do it again? Take the same time and go in the same direction? Try restarting the ant several times. And notice what happens, because its important. If we start over ... the same thing happens. Exactly the same thing. Langton's ant is therefore a "deterministic" system.

Set Up Barriers

So, what's the big deal? Maybe Langton's ant just has a whole long list of instructions saying exactly what to do on each turn: first do this, then do that, then do the other thing, and so on ... with the detailed instructions for building a road at the end. The ant might look like it has a purpose, but that's just because someone put all those instructions in it. Perhaps, but if that were the case then what should happen if we disturb things a little? or a lot? Try putting some things in the ant's way, by clicking on "Create Barrier" and drawing on the arena. (You can put in barriers before you start the ant moving, or stop the ant moving, add barriers, and then start it again. You can also remove barriers by turning off "Create Barrier" and turning on "Remove Barrier". And use the displayed X and Y coordinates of mouse location to make/remove barriers at particular locations).

How Could One Explain That?

Now THAT's interesting, no? The ant pretty much always ends up building a road (always?) but when and where it starts and what direction it goes in depends on what barriers you've added to the arena.
A Side Project

Try putting barriers in lots of different places. How much variation is there in when and where the road starts and in what direction it goes in?

Try systematically varying the location and number of barriers. Is there any relation between the location and/or number of barriers and when/where the ant starts building a road? On the direction it goes in when it does?

So the ant can't simply be following a long set of instructions that say do this, then that, then that, and so forth. The ant does different things on different turns depending on what it encounters. And ends up building roads starting from different places and going in different directions. But usually (always?) it builds a road. Its a pretty stubborn ant, no? No matter how much you try to disturb it, it does pretty much the same thing. So maybe it really does have a purpose?

Maybe its time to look inside the ant? Spend a little time trying to imagine what's inside the ant that causes it to do what it does. Then let's go see what's there, and how it works.

"The World of Langton's Ant" was produced by Paul Grobstein with the Summer 2005 Serendip/SciSoc group. Applets were created with NetLogo by Rebekah Baglini, building on earlier work. Our thanks to the Emergent Systems Working Group for fertile conversations from which this emerged and to which we hope it further contributes.
Looking Inside
Agents/Environments | Observers | Architects | Beyond Determinism?
Summary and ...
Further reflections on Emergence and Science Education
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