Glider synthesis/Snippet

Glider synthesis (or glider construction) is the construction of an object by means of glider collisions. It is generally assumed that the gliders should be arranged so that they could come from infinity - that is, gliders should not have had to pass through one another to achieve the initial arrangement.

Four main characterizing features of a synthesis are the geometry, reaction speed, reaction multiplicity, and glider cost. Of particular interest is slow salvo synthesis: unidirectional synthesis where every stage has a glider cost of one, and thus the number of stages (i.e., the multiplicity) is equal to the total cost. Perhaps surprisingly, anything that is glider synthesizable is also slow salvo synthesizable.

In the 1990s, glider syntheses for all still lifes and known oscillators with at most 14 cells were found by David Buckingham. Almost all of these were successfully reduced to a synthesis cost of less than 1 glider per live cell, or "1 glider per bit". A collaborative effort ending in May 2014 completed glider syntheses of all still lifes with 17 or fewer cells. A second, longer effort completed all the 18-bit still lifes in November 2014. Later optimization projects reduced the maximum cost of construction for 15-bit and 16-bit still lifes to less than one glider per bit.