Day and Night is a

cellular automaton A cellular automaton (pl. cellular automata, abbrev. CA) is a discrete model of computation studied in automata theory. Cellular automata are also called cellular spaces, tessellation automata, homogeneous structures, cellular structures, tessel ...

rule in the same family as Game of Life. It is defined by rule notation B3678/S34678, meaning that a dead cell becomes live (is born) if it has 3, 6, 7, or 8 live neighbors, and a live cell remains alive (survives) if it has 3, 4, 6, 7, or 8 live neighbors, out of the eight neighbors in the

Moore neighborhood In cellular automata, the Moore neighborhood is defined on a two-dimensional square lattice and is composed of a central cell and the eight cells that surround it. Name The neighborhood is named after Edward F. Moore, a pioneer of cellular aut ...

. It was invented and named by Nathan Thompson in 1997, and investigated extensively by David I. Bell. The rule is given the name "Day & Night" because its ''on'' and ''off'' states are symmetric: if all the cells in the Universe are inverted, the future states are the inversions of the future states of the original pattern. A pattern in which the entire universe consists of ''off'' cells except for finitely many ''on'' cells can equivalently be represented by a pattern in which the whole universe is covered in ''on'' cells except for finitely many ''off'' cells in congruent locations. Although the detailed evolution of this cellular automaton is very different from Conway's Game of Life, it exhibits complex behavior similar to that rule: there are many known small ''

oscillators Oscillation is the repetitive or periodic variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples of oscillation include a swinging pendulum ...

'' and ''

spaceships Spaceship may refer to: Spaceflight * Space vehicle, the combination of launch vehicle and spacecraft * Spacecraft, a craft, vehicle, vessel or machine designed for spaceflight * Starship, a spacecraft built for interstellar flight Computing ...

'', and ''

guns A gun is a device that propels a projectile using pressure or explosive force. The projectiles are typically solid, but can also be pressurized liquid (e.g. in water guns or cannons), or gas (e.g. light-gas gun). Solid projectiles may be ...

'' formed by combining oscillators in such a way that they periodically emit spaceships of various types.

References

* . See also Bell'
Day & Night pattern archive
Cellular automaton rules {{comp-sci-theory-stub