Conway’s Game of Life has no CPU, no variables and no instruction set. Paul Rendell built a computer in it anyway.
Visit Paul Rendell’s Game of Life work
Rendell’s site documents a Turing machine constructed entirely from patterns inside John Conway’s cellular automaton. The original machine is dated April 2, 2000 and uses the collisions and timing of Game of Life objects to implement the pieces a computer needs: memory, addressing, control logic and a tape.
The first working design is deliberately small. It has three states and three symbols. One machine cycle takes 11,040 generations of Life.
That is not fast.
Speed is not the point.
Logic made from moving dots
The detailed pages break the machine into components with names that sound half like computer engineering and half like astronomy: finite state machine, signal detector, stack cell, comparator, fanout, glider gun, lightweight spaceship gun and output collator.
The tape is implemented as two stacks. Memory cells store patterns of gliders. Rows and columns address the finite-state-machine matrix. Carefully timed collisions create, destroy or redirect the signals that carry information.
The machine is computation reduced to geometry and timing.
Rendell also made the design expandable. The early version could be enlarged to as many as 16 states and eight symbols, enough capacity for a universal machine. In 2010 he documented a Universal Turing Machine in Life, and in 2011 a fully universal version whose stack could continue growing during operation.
One image on the later site shows the fully universal machine after 149 million generations.
That sentence feels excessive until you remember the computer itself is made out of a mathematical toy whose only rule is whether cells live or die based on their neighbors.
The pages preserve downloadable patterns, diagrams, animations, Java tools and explanations of the individual logic structures. That makes the archive more useful than a video of a giant Life pattern doing something mysterious. A reader can trace the design down into gates and memory cells.
This is exactly the kind of technical Web project that deserves to remain linkable. It sits at the intersection of recreational mathematics, computer architecture and pure stubbornness.
A modern processor hides billions of transistors under packaging.
Rendell’s machine does the opposite. It turns computation into an enormous visible contraption and invites you to inspect every moving part.