# Glider

Glider
Pattern type Spaceship
Number of cells 5
Bounding box 3×3
Frequency class 1.8
Direction Diagonal
Period 4
Mod 2
Speed c/4
Speed (unsimplified) Unknown
Heat 4
Discovered by Richard K. Guy
Year of discovery 1970
For other meanings of the term 'glider', see Glider (disambiguation).

The glider (or featherweight spaceship) is the smallest, most common, and first-discovered spaceship. It travels diagonally across the Life grid at a speed of c/4. Gliders are important because they are easily produced (for an example see the Gosper glider gun), can be collided with each other to form more complicated objects (see glider synthesis), and can be used to transmit information over long distances.

Its name is due in part to the fact that it is glide symmetric; however, John Conway has stated he regrets calling it a glider, saying it looks more like an ant walking across the plane.[1]

## Discovery

The glider was found by Richard K. Guy in 1970 while Conway's group was attempting to track the evolution of the R-pentomino. It is often wrongly stated that John Conway discovered the glider, but Conway himself has said that it was Guy, a fact expounded in Conway's biography, Genius at Play:[2]

## Commonness

The glider is often produced by randomly-generated starting patterns;[3] it is the fourth most common object on Adam P. Goucher's Catagolue.[4]

## Glider synthesis

Main article: Glider synthesis

Glider synthesis 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.[5]

Glider syntheses for all still lifes with at most 18 cells[6][7] and known oscillators with at most 14 cells have been explicitly constructed.

## Colour of a glider

The colour (or parity) of a glider is a property of the glider which remains constant while the glider is moving along a straight path, but which can be changed when the glider bounces off a reflector. It is an important consideration when building something using reflectors.

To define the colour of a glider, first choose some cell to be the origin. This cell is then considered to be white, and all other cells to be black or white in a checkerboard pattern (i.e. the cell with coordinates (m,n) is white if m+n is even, and black otherwise). Then the colour of a glider is the colour of its leading cell when it is in the following phase:

A reflector which does not change the colour of gliders obviously can not be used to move a glider onto a path of different colour than it started on. However, a 90-degree reflector which does change the colour of gliders is similarly limited, as the colour of the resulting glider will depend only on the direction of the glider, no matter how many reflectors are used. For maximum flexibility, therefore, both types of reflector are required.[8]