Three cells above decide one cell below, eight black-and-white combinations, eight bits: exactly 256 possible rules and no more. Among them Rule 90 takes the XOR of its two neighbours and draws the Sierpinski triangle, Rule 30 pours out of a single black cell a pattern so random-looking that its centre column was once used as a source of random numbers, and Rule 110 has been proved able to compute anything a computer can. Stephen Wolfram sorted the behaviour of those 256 rules into four classes, from dead to periodic to chaotic to complex.
Three cells above decide one cell below, eight black-and-white combinations, eight bits: exactly 256 possible rules and no more. Among them Rule 90 takes the XOR of its two neighbours and draws the Sierpinski triangle, Rule 30 pours out of a single black cell a pattern so random-looking that its centre column was once used as a source of random numbers, and Rule 110 has been proved able to compute anything a computer can. Stephen Wolfram sorted the behaviour of those 256 rules into four classes, from dead to periodic to chaotic to complex.
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