The incredible shrinking glider

The gates in the previous pages are pretty bulky. That's not terribly surprising, though. They operate on gliders and the gliders are pretty bulky with each of them needing dozens of grid cells for themselves and the needed spaces around them. The shift from the original Life rules helped simplify matters. Another shift of rules may help again. Consider a new set of rules. Each grid cell can be black, white, red or blue. The black cells are totally inert. They never change; they can neither be created nor changed. If a cell is white it will turn blue. If a cell is blue it will turn red. If a cell is red and has one or two white neighboring cells, then it will turn white.

These rules allow for "electrons" that travel along "wires". The wires are strings of red cells that branch and loop. The electrons are a pair of cells with a white one at the head and a blue one at the tail. Electrons split into two at forks in the road. They can be systematically created by loops. The wire can steer the electrons around corners without the need for additional structure.

It's useful to be able to create one-way streets. Notice that the electrons make it to the end of the top wire on the right but do not make it to the bottom wire. Both wires have a "diode" on them. A diode is a structure that allows a signal to flow one way and not the other way. The two diodes are identical except that the one on the top is pointing forwards and the one on the bottom is pointing backwards.

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Brian Silverman
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