A gun is a stationary pattern that repeatedly emits spaceships (or rakes) forever. By far the most common type of guns are glider guns, which emit gliders (the most well-known of which is the Gosper glider gun); however, guns that emit spaceships of other speeds, including c/2 orthogonal, 2c/5 orthogonal, and c/12 diagonal, have also been created.
The first gun to be discovered, the Gosper glider gun, was found by Bill Gosper in 1970, being the first known pattern in Conway's Game of Life to exhibit infinite growth. Since then, many guns have been constructed with various periods and that fire spaceships of various speeds. Due to simple glider syntheses of the standard spaceships many c/2 spaceship guns are known. The first gun that did not fire gliders or c/2 spaceships was a Cordergun (a gun that fires Corderships) constructed by Jason Summers in July, 1999 based on a synthesis of a variation of the 7-engine Cordership by Stephen Silver. In March, 2003 Noam Elkies completed the synthesis of 60P5H2V0 which Dave Greene used to construct the first 2c/5 spaceship gun in April of the same year.
In July, 2010 Dave Greene constructed a few guns for a geminoid spaceship. These are the first guns that shoot obliquely-traveling spaceships and at the time were the largest patterns constructed in Life, in terms of their bounding boxes.
On February 17, 2013 Josh Ball discovered a simple c/7 orthogonal spaceship, loafer. Adam P. Goucher found a synthesis for the loafer later that day, allowing the construction of c/7 orthogonal spaceship guns.
The barrel of a gun (or rake) is a path along which spaceships travel. The term is most commonly used in the context of the number of barrels a gun or rake possesses, which is the number of distinct spaceship streams emitted by said gun or rake. For example, the AK-94, B-52 bomber and Simkin glider gun are said to be double-barrelled because they produce two streams of gliders. The period-256 glider gun and Gunstar and its variants all have four barrels, and P94S contains 12 barrels. Given a gun with multiple barrels, one can eliminate barrels by simply placing an eater 1 in the path of the unwanted glider streams.
A pseudo-period gun (as opposed to a true-period gun) is a gun that emits a period n stream of spaceships (or rakes) via a mechanism that oscillates with a period different from n -- this period will necessarily be a multiple of n. Pseudo period n glider guns are known to exist for all periods greater than or equal to 14, with smaller periods being impossible. The first pseudo period 14 gun was built by Dietrich Leithner in 1995.
A true-period gun (as opposed to a pseudo-period gun) is a gun that emits a period n stream of spaceships (or rakes) via a mechanism that oscillates with period equal to n. True period n guns are known to exist for all periods greater than 53 and all composite periods greater than 39, plus 43. Periods below 39 with known guns are 20, 21, 22, 24, 27, 28, 30, 32, 33, 36, and 37. Credits for gun periods below 62 are as follows:
|Period||Discoverer||Year of discovery|
|20||Matthias Merzenich and Noam Elkies||2013|
|21||Tanner Jacobi and David Raucci||2021|
|22||David Eppstein and Jason Summers||2000|
|27||David Raucci and goldenratio||2022|
|28||Matthias Merzenich and Paul Callahan||2020|
|32||Matthias Merzenich, David Raucci, praosylen, wwei23, and Noam Elkies||2021|
|33||Arie Paap and Matthias Merzenich||2018|
|37||iNoMed, goldenratio, and Luke Kiernan||2022|
|40||Adam P. Goucher, Jason Summers, and Matthias Merzenich||2013|
|42||Tanner Jacobi and David Raucci||2021|
|49||Tanner Jacobi, wwei23, and hotcrystal0||2021|
|50||Dean Hickerson and Noam Elkies||1996|
|51||Luka Okanishi, wwei23, and hotcrystal0||2021|
|52||Dave Greene, Chris Cain, Matthias Merzenich and Adam P. Goucher||2018|
|58||thunk, Matthias Merzenich, and Chris Cain||2016|
|59||Adam P. Goucher and Jason Summers||2009|
Smallest guns by area of bounding box
A collection of smallest guns by bounding box area was originally created and maintained by Dietrich Leithner and Peter Rott, before Jason Summers took over the maintenance. The p14-999 collection had subsequently evolved into a Git repository led by Chris Cain. Currently, the collection is maintained collaboratively at Catagolue's glider-synthesis database.
- Current database (Catagolue)
- older repository maintained by Chris Cain (only p14-1024)
- older version maintained by Jason Summers (includes some periods in the range p1000-9999).
Guns in Life-like cellular automata
Due to the existence of some small spaceships in Life-like cellular automata with birth at two live neighbours (B2), many low-period spaceship guns have been found using tools such as WinLifeSearch. In contrast, there are very few outer-totalistic rules without B2 (and B0) that are known to contain guns. The following is a list of outer-totalistic rules with neither B0 nor B2 that have known guns:
- Dieter and Peter's glider gun collection
- Glider gun true-periods status table
- Gun pseudo-periods status table
- List of guns
- "Game of Life Status page". Retrieved on October 15, 2010.
- Gemini guns at Game of Life News. Posted by Adam P. Goucher on July 30, 2010.
- Shannon Omick (February 18, 2013). Re: c/7 orthogonal spaceships (discussion thread) at the ConwayLife.com forums
- Alexey Nigin (March 6, 2016). Re: is this c/10 spaceship known? (discussion thread) at the ConwayLife.com forums
- Goldtiger997 (October 22, 2019). Re: Stable signal converters (discussion thread) at the ConwayLife.com forums
- Entity Valkyrie (January 26, 2020). Re: Small Spaceship Syntheses (discussion thread) at the ConwayLife.com forums
- Entity Valkyrie (May 22, 2020). Re: Construction practice (discussion thread) at the ConwayLife.com forums
- Dave Buckingham (October 12, 1996). "My Experience with B-heptominos in Oscillators". Retrieved on May 14, 2009.
- Matthias Merzenich (Sokwe) (April 11, 2013). "Guns in Life-like cellular automata".