table based on rules decides what the cell has to do next. So, in a black-and-white automaton, it could be that if all neighboring squares are black, the central square is made white. Despite the apparent simplicity of this setup, it turned out that anything achieved in von Neumann’s original automaton could be aped by Ulam’s cellular system.
After von Neumann’s death, the torch for cellular automata passed to others, notably to John Holland, professor of Psychology and professor of Electrical Engineering and Computer Science at the University of Michigan, Ann Arbor. In 1960, Holland outlined an “iterative circuit computer” related to cellular automata that could mimic genetic processes. Despite the dry title, this research captured the public imagination. As one newspaper put it, “He’s the man who taught computers how to have sex.” This logical view of life now began to take hold and multiply in the minds of researchers in other laboratories. One of the best known is the British mathematician John Conway.
For several months in the late 1960s, the mathematics department at Cambridge University was taken over by Conway’s efforts to find a hypothetical machine that could build copies of itself. From a small table an assortment of poker chips, foreign coins, cowrie shells, and whatever else came to hand was used to mark out the “living” squares in patterns that spread across the floor of the common room as the rules were enacted during each tea break. Even then, Conway used a computer to study particularly long-lived populations.
In 1970 he unveiled his Game of Life. Now Conway had selected the rules of his automata with great care to strike a delicate balance between two extremes: the many patterns that grow quickly without limit and those that fade away rapidly. The evocative name reflected Conway’s fascination with how his combination of a few rules could produce global patterns that would expand, morph shape, or die out unpredictably.
Some people call it the “God Game” in recognition of how players have a toy universe at their beck and call. Taking part is easy, requiring no miracles, religious followings, or holy books. Imagine a checkerboard with counters in a few of the squares. Then follow these simple rules. If an empty square has three occupied neighbors (this includes the diagonal as well as adjacent sites), it comes “alive,” nurtured by its neighbors. If a square has two occupied neighbors, then it remains unchanged. Finally, if an occupied square has any other number of occupied neighbors, then it loses its counter—to anthropomorphize, the cell dies pining for neighborly love and the chance to cooperate.
Conway conjectured that no initially finite population could grow in number without limit and offered fifty dollars for the first proof or disproof. The prize was won in November 1970 by a group in the Artificial Intelligence Project at the Massachusetts Institute of Technology, which discovered a “glider gun,” a pattern that every thirty moves ejects a glider, a moving pattern consisting of five counters. Since each glider added five more counters, the population could grow without limit. Intersecting gliders were found to produce fantastic results, giving birth to strange patterns that in turn spawned still more gliders. Sometimes the collisions expanded to digest all guns. In other cases, the collision mass destroyed guns by “shooting back.”
The patterns produced can be complex; indeed the cellular automaton can be shown to be equivalent to a universal Turing machine, so the Game of Life is theoretically as powerful as any computer. It does not take much imagination to see that cellular automata provide a powerful tool to study the patterns of nature. Stephen Wolfram—who wrote his first paper at the age of sixteen and went up to study at the University of Oxford at the age of seventeen, and who devised a highly successful software application called Mathematica as well as a new kind of search engine (Wolfram Alpha)—turns this idea on its head in his book A New Kind of Science
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