Gun

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 known gun, the Gosper glider gun

History

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[1] 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.[2] 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 loafer later that day, allowing the construction of c/7 orthogonal spaceship guns.[3]

During March 2016 the copperhead spaceship was discovered, with a glider synthesis and several guns following suit.[4]

In 2019 and 2020 guns were produced for the spaceships 46P4H1V0,[5] spider,[6] and 58P5H1V1,[7] of speeds c/4 orthogonal, c/5 orthogonal, and c/5 diagonal respectively.

Barrels

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 a whopping 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.

Pseudo-period guns

A pseudo-period gun (as opposed to a true-periodgun) 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.

True-period guns

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[8], but only a few smaller periods have been achieved, namely 20, 22, 24, 30, 33, 36, 40, 44, 45, 46, 48, 50, 52. Credits for gun periods below 62 are as follows:

Period Discoverer Year of discovery
20 Matthias Merzenich and Noam Elkies 2013
22 David Eppstein and Jason Summers 2000
24 Noam Elkies 1997
30 Bill Gosper 1970
33 Arie Paap and Matthias Merzenich 2018
36 Jason Summers 2004
40 Adam P. Goucher, Jason Summers, and Matthias Merzenich 2013
44 David Buckingham 1992
45 Matthias Merzenich 2010
46 Bill Gosper 1971
48 Noam Elkies 1997
50 Dean Hickerson and Noam Elkies 1996
52 Dave Greene, Chris Cain, Matthias Merzenich and Adam P. Goucher 2018
54 Dietrich Leithner 1998
55 Stephen Silver 1998
56 Dietrich Leithner 1998
57 Matthias Merzenich 2016
58 thunk and Matthias Merzenich 2016
59 Adam P. Goucher and Jason Summers 2009
60 Bill Gosper 1970
61 Luka Okanishi 2016

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:

  • Glider guns[9]
    • B3/S23 (Conway's Game of Life)
    • B3/S236
    • B3/S2367
    • B3/S23678
    • B3/S2368
    • B3/S237
    • B3/S2378
    • B3/S238 (EightLife)
    • B36/S23 (HighLife)
    • B36/S237
    • B36/S2378
    • B36/S238
    • B368/S23
    • B368/S238 (LowDeath)
    • B37/S23 (DryLife)
    • B37/S236
    • B37/S237
    • B37/S238
    • B378/S23 - no explicit constructions exist
    • B378/S237
    • B378/S2378
    • B378/S238
    • B38/S236
    • B38/S2367
    • B38/S23678
    • B38/S2368
    • B38/S23 (Pedestrian Life)
    • B38/S237
    • B38/S2378
    • B38/S238 (HoneyLife)
  • Other guns
    • B3/S23 (Conway's Game of Life)
    • B3/S237
    • B3/S2378
    • B3/S238 (EightLife)
    • B35/S236
    • B358/S236
    • B36/S23 (HighLife)
    • B36/S237
    • B36/S2378
    • B36/S238
    • B368/S23
    • B368/S238 (LowDeath)
    • B36/S245 (Logarithmic replicator rule)
    • B368/S245 (Move)
    • B368/S12578
    • B3678/S34678 (Day & Night)
    • B37/S23 (DryLife)
    • B37/S238
    • B378/S23
    • B378/S238
    • B38/S23 (Pedestrian Life)
    • B38/S237
    • B38/S2378
    • B38/S238 (HoneyLife)
gollark: That's some cheatiness right there!
gollark: https://dragcave.net/progeny/BOO
gollark: It's been bred three times?
gollark: Hmm. Weird.
gollark: It's not "Verified Thuwed", look.

See also

References

  1. "Game of Life Status page". Retrieved on October 15, 2010.
  2. Adam P. Goucher (July 30, 2010). "Gemini guns". Retrieved on October 15, 2010.
  3. Shannon Omick (February 18, 2013). Re: c/7 orthogonal spaceships (discussion thread) at the ConwayLife.com forums
  4. Alexey Nigin (March 6, 2016). Re: is this c/10 spaceship known? (discussion thread) at the ConwayLife.com forums
  5. Goldtiger997 (October 22, 2019). Re: Stable signal converters (discussion thread) at the ConwayLife.com forums
  6. Entity Valkyrie (January 26, 2020). Re: Small Spaceship Syntheses (discussion thread) at the ConwayLife.com forums
  7. Entity Valkyrie (May 22, 2020). Re: Construction practice (discussion thread) at the ConwayLife.com forums
  8. Dave Buckingham (October 12, 1996). "My Experience with B-heptominos in Oscillators". Retrieved on May 14, 2009.
  9. Matthias Merzenich (Sokwe) (April 11, 2013). "Guns in Life-like cellular automata".
  • Gun at Wikipedia
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