Collision

A collision is an interaction between two or more patterns that are initially disjoint and non-interacting.

It is often possible to rewind a collision back in time by finding predecessors for each of the participating patterns, while preserving the moment of first interaction.

Frequently discussed types of collisions include collisions between spaceships (for example glider syntheses), collisions between a spaceship and a stationary pattern (for example one-glider seeds), collisions between several spaceships and a stationary pattern (for example synthesis components).

Less frequently, "collision" may refer to an arbitrary pattern interaction (for example, the interaction between queen bee shuttles in the Gosper's glider gun).

Glider collisions

See also: Glider synthesis, 2-glider collision, 3-glider collision, 4-glider collision

Collisions between gliders are frequently discussed in the context of glider synthesis and glider constructibility, where the aim is either to construct a specific object or pattern or to prove that it cannot be constructed.

In Life, there are 71 two-glider collisions. With three or more gliders, it is possible to construct an unbounded number of different patterns with different bounding boxes, for example pairs of traffic lights separated by different distances. With three gliders, it is still possible to describe the set of three-glider collisions systematically, as infinite families of collisions along with a finite set.

Other rules

For alien rules, the number of two-glider collisions may depend on the specific rule; the set of collisions with three or more gliders also depends on the evolution of each of two-glider collisions. The Life's glider works in 2⁸² isotropic rules expressible with Hensel notation (all of birth conditions in B2ikn3cekqry4aceijknqtwyz5aceijkqry678 and all of survival conditions in S02cikn3aceikqy4aceijnqrtwyz5678 are optional). The set of two-glider collisions in a rule depends on presence of certain of these conditions (B2i, B2k, B2n); below are shown examples of collisions that are not collisions in Life.

x = 13, y = 7, rule = B2i34c/S2-i3 obo$b2o$bo2$11bo$10bo$10b3o! #C [[ THUMBSIZE 2 THEME 6 GRID GRIDMAJOR 0 SUPPRESS THUMBLAUNCH ]] #C [[ HEIGHT 600 THUMBSIZE 4 ZOOM 24 X -1 Y 6 THEME Book GPS 15 AUTOSTART T 0 PAUSE 1 T 20 PAUSE 5 T 79 PAUSE 1 LOOP 80 ]] A B2i-dependent 2G collision in Salad (B2i34c/S2-i3) (click above to open LifeViewer)

x = 14, y = 7, rule = B2k34c/S2-c34z8 11bobo$11b2o$12bo2$bo$2bo$3o! #C [[ THUMBSIZE 2 THEME 6 GRID GRIDMAJOR 0 SUPPRESS THUMBLAUNCH ]] #C [[ HEIGHT 600 THUMBSIZE 4 ZOOM 24 Y 6 THEME Book GPS 15 AUTOSTART T 0 PAUSE 1 T 20 PAUSE 5 T 79 PAUSE 1 LOOP 80 ]] A B2k-dependent 2G collision in Simple Life (B2k34c/S2-c34z8) (click above to open LifeViewer)

x = 15, y = 7, rule = B2n3/S23-q 12bobo$12b2o$13bo2$bo$2bo$3o! #C [[ THUMBSIZE 2 THEME 6 GRID GRIDMAJOR 0 SUPPRESS THUMBLAUNCH ]] #C [[ HEIGHT 600 THUMBSIZE 4 ZOOM 24 X 1 Y 6 THEME Book GPS 15 AUTOSTART T 0 PAUSE 1 T 20 PAUSE 5 T 103 PAUSE 1 LOOP 104 ]] A B2n-dependent 2G collision in LeapLife (B2n3/S23-q) (click above to open LifeViewer)

Also see

• Collisions of a glider with common objects
• gencols
• QuFince