artificial life

Chapter 2: Origins of Artificial Life

2.3 Langton Loops

For decades von Neumann's virtual creature was reviewed, criticized and reworked, but still no one actually attempted to implement an artificial creature able to reproduce itself. Chris Langton, an a-life enthusiast took it upon himself to create a creature that fulfilled Von Neumann's criteria of reproduction.

Starting with a paper that discussed a simplification of von Neumann's beast, Langton simplified the model further. Langton's creature contained cells that had only 8 different states, a huge simplification over the original 29. His idea also greatly simplified the mechanics of the creature, reducing it to a bare minimum. Most importantly, Langton felt that he could model the creatures on a computer, providing a chance to actually see the theory in action.

The "organism" that Langton created lived in an environment that was nothing more than a board of cells; each cell contains its own state. Depending upon the state of a cell and the state of the cells around it, a cell's state might change in the next generation. The creature that Langton created in this environment looked like a loop with a tail. As time advanced the tail extended and made a new loop. This new loop then severed itself from the original loop organism and then there were two organisms. Both the new creature and the original creature were able to reproduce, and so they did, eventually filling up all the available space [Levy, 1992]. Figure 2.1 shows some Langton Loops in the process of regenerating.

Langton's loops have been compared to coral because each new generation builds upon the husks of the generation before. The "colony" eventually grows so large that it takes up the entire environment space.

Even though this fulfilled von Neumann's criteria of reproduction, no one was about to claim that it was a form of life. However, it did prove that automata could be made to reproduce and it was a huge step forward for a-life.