# Spaceship

**spaceship**(also referred to as a

**glider**

^{[1]}or less commonly a

**fish**

^{[2]}, and commonly shortened to "ship") is a finite pattern that returns to its initial state after a number of generations (known as its period) but in a different location.

## Contents

## Spaceship Speed

*Main article: Speed*

The speed of a spaceship is the number of cells that the pattern moves during its period divided by the period length. This is expressed in terms of *c* (the metaphorical "speed of light") which is one cell per generation; thus, a spaceship with a period of five that moves two cells to the left during its period travels at the speed of 2c/5. Until the construction of Gemini in May 2010, all known spaceships in Life traveled either orthogonally (only horizontal or vertical displacement) or diagonally (equal horizontal and vertical displacement); other oblique spaceships have been constructed since then, e.g. waterbear and the Parallel HBK. It is known that Life has spaceships that travel in all rational directions at arbitrarily slow speeds (see universal constructor). Spaceships traveling in other directions and at different speeds have also been constructed in other two dimensional cellular automata.^{[3]} The maximum speed for Life is c/2 orthogonal and c/4 diagonal^{[4]} (and continually, c/6 for slope 2, c/8 for slope 3, etc.); however, certain agar crawlers such as lightspeed wire can break this speed in their respective medium.

## Spaceship types

*Main article: List of spaceships*

Spaceships are most commonly sorted by their speed and direction, and sometimes their period. They can be separated into three fundamental categories:

### Elementary spaceships

*Elementary spaceships* are the smallest classification of spaceships. This class consists of ships found by direct computer search, such as the weekender, as well as ships composed of a small number of natural moving components, such as Corderships. Despite their generally small size, only a few of them have been known to have emerged from soups. Constructing guns for these spaceships is usually difficult, as only a few elementary spaceships have known glider syntheses; those who do generally require a lot of gliders in awkward positions. Only elementary spaceships which move orthogonally or diagonally have been found; there are currently no known elementary knightships (however, there have been some close calls).

Speed | Direction | Smallest known | Minimum # of cells | |
---|---|---|---|---|

c/2 | orthogonal | lightweight spaceship | 9 | |

3c/7 | orthogonal | spaghetti monster | 702 | |

2c/5 | orthogonal | 30P5H2V0 | 30 | |

c/3 | orthogonal | 25P3H1V0.2 | 25 | |

2c/7 | orthogonal | weekender | 36 | |

c/4 | orthogonal | 37P4H1V0 | 37 | |

c/5 | orthogonal | spider | 58 | |

c/6 | orthogonal | 56P6H1V0 | 56 | |

c/7 | orthogonal | loafer | 20 | |

c/10 | orthogonal | copperhead | 28 | |

c/4 | diagonal | glider | 5 | |

c/5 | diagonal | 58P5H1V1 | 58 | |

c/6 | diagonal | 77P6H1V1 | 77 | |

c/7 | diagonal | lobster | 83 | |

c/12 | diagonal | 4-engine Cordership | 134 |

### Engineered spaceships

*Engineered spaceships*, also known as *caterpillars* after the first known engineered spaceship, are defined as spaceships consisting of many small interacting components.^{[5]} Almost all engineered spaceships are composed of hundreds of thousands to well over millions of active cells. Engineered spaceships still have fixed speeds, and tend to rely on "crawlers", reactions in which a pattern reacts with another pattern, producing both the patterns in different positions; such as the pi crawler.

Speed | Direction | Smallest known | Minimum # of cells | |
---|---|---|---|---|

17c/45 | orthogonal | caterpillar | 11,880,063 | |

31c/240 | orthogonal | centipede | 620,901 | |

(23,5)c/79 | slope 23/5 | waterbear | 197,896 |

### Engineerable spaceships

*Engineerable spaceships* (or *adjustable spaceships*) are the third class of spaceships. Although on average smaller than the engineered spaceships, their magic comes from having (to an extent) adjustable features, usually speed. With some almost always trivial modifications, these spaceships can be made to travel at different velocities and even directions. Rather than being searched for, programs exist that explicitly construct the spaceships. Engineerable spaceships can run on engineerable reactions, such as the half-bakery and glider reaction, or by reading instruction tapes, such as Gemini. Families of engineerable spaceships include the geminoids, demonoids, half-baked knightships and caterloopillars.

Speed | Direction | Smallest known | Minimum # of cells | |
---|---|---|---|---|

31c/240 | orthogonal | centipede caterloopillar | 361,070 | |

c/8 | orthogonal | Original caterloopillar | 232,815 | |

All speeds slower than c/4 | orthogonal | other caterloopillars | Varies | |

(5120,1024)c/16849793 | slope 5 | Gemini | 846,278 | |

(3072,1024)c/36000001 | camelwise | Gemini 3 | <=850932 | |

(4096,2048)c/17783745 | knightwise | Gemini 2 | <=872252 | |

(6,3)c/245912 | knightwise | Parallel HBK | 132,945 | |

(6,3)c/2621440 | knightwise | Half-baked knightship | 1,049,395 | |

65c/438852 | diagonal | 0hd Demonoid | 27,250 | |

65c/818356 | diagonal | 10hd Demonoid | 47,701 |

### Other classifications

*Main article: Spaceship types*

Although spaceships are most commonly categorized by their speed and direction, other categorizations have been applied to spaceships based on their appearances, components, or other properties. One such categorization is the symmetry of spaceships: spaceships can be bilaterally symmetric (e.g. copperhead), exhibit glide symmetry (e.g. glider), or simply be asymmetric (e.g. loafer). Other somewhat subjective categorizations have also been made, such as greyships, spaceships filled with large amounts of static, live cells, or smoking ships, which produce large sparks, a notable example being the Schick engine. A spaceship may also support other components which would not function as spaceships on their own. Given a freestanding spaceship, such additional components are often referred to as tagalongs; however they can be attached to any side of a spaceship, such as pushalong 1 and sidecar. Unstable spaceships immersed in a sustaining cloud are known as flotillae. A well known example is that of the overweight spaceships, which are unstable alone but may be 'escorted' by two or more smaller spaceships.

## History

### 1970s

The four smallest spaceships in life, the glider, lightweight spaceship, middleweight spaceship and heavyweight spaceship, were all found by hand in 1970. For almost twenty years spaceship development was limited to adding tagalongs to the known c/2 spaceships, such as the Schick engine.

### 1980s

Significant advances in spaceship technology came in 1989, when Dean Hickerson began using automated searches based on a depth-first backtracking algorithm. These searches found orthogonal spaceships with speeds of c/3 and c/4, new c/2 ships, and the first spaceship other than the glider to travel at the speed of c/4 diagonally, dubbed the big glider.

### 1990s

Hickerson continued to find new spaceship speeds, the first of this decade being 2c/5 orthogonal, plus several ways to combine switch engines to create the first c/12 diagonal spaceships, named Corderships in honour of Charles Corderman.

The next spaceship speed to be discovered was that of the orthogonal c/5 snail, found by Tim Coe in 1996, with a program he had designed using breadth-first searching, and which could split tasks between multiple CPUs.^{[6]} In the following year, David Bell found the much smaller c/5 spider using lifesrc, a program based on Hickerson's search algorithm.^{[7]}

In March of 1998 David Eppstein created gfind, a breadth-first program that uses a depth-first search to limit the size of the search queue.^{[8]}

### 2000s

Eppstein put his search program to good use in 2000, discovering the first spaceship that travels at the speed of 2c/7 orthogonally, the weekender. A search by Paul Tooke using the same program found the first c/6 orthogonal spaceship, the dragon, later that year. Also in 2000, Jason Summers found the first c/5 diagonal spaceship using David Bell's lifesrc program.

In 2004 Gabriel Nivasch, with the help of Jason Summers and David Bell, finished construction on the caterpillar, the first known orthogonal 17c/45 spaceship, which made use of the 17c/45 reaction.

### 2010s

In May 2010 Andrew J. Wade created a universal constructor-based spaceship, Gemini, which travels at a speed of (5120,1024)c/33699586.^{[9]} This was the first explicitly constructed spaceship in Life to travel in an oblique direction, and also yielded the first explicit method of constructing arbitrarily slow spaceships.

In Febuary 2013, the first c/7 orthogonal spaceship, loafer, was discovered by Josh Ball.

2014 provided a handful of new engineered spaceships, using various new technologies. In July, several half-bakery-based knightships were constructed with a new technique not requiring universal-constructor circuitry. These produced spaceships that were both much slower and much smaller than the Gemini variants. In September, Dave Greene and Chris Cain completed two 31c/240 orthogonal spaceships, along the same general lines as the original Caterpillar but using a number of new mechanisms. Finally, in December, an oblique caterpillar dubbed the Waterbear was completed by Brett Berger, traveling at (23,5)c/79. Richard Schank discovered pufferfish, a c/2 puffer, and Ivan Fomichev found a c/2 fuse for its exhaust and combined two pufferfish with fuses to assemble the first wholly high-period c/2 spaceship.

In December 2015, Chris Cain completed a diagonal self-constructing spaceship -- a "0hd Demonoid" -- based on Geminoid technology, adapted from a larger 10hd version constructed in November in collaboration with Dave Greene.

In March 2016, forum user 'zdr' discovered copperhead, an extremely small c/10 spaceship. A pseudo-tagalong for this spaceship, alongside many other c/10 technologies, were constructed within two months after the discovery of the ship.

In April 2016 Michael Simkin finished the adjustable caterloopillar project, making it possible to build spaceships of arbitrary orthogonal speeds slower than c/4.

In June 2016 Tim Coe found a large elementary 3c/7 orthogonal spaceship, 702P7H3V0.

## See also

- List of spaceships
- Spaceship flotilla
- Spaceship periods status table
- Spaceship terminology
- Types of spaceships
- Velocities of spaceships and related objects status table
- Spaceships of HighLife

## Notes

- ↑ "Glider".
*The Life Lexicon*. Stephen Silver. Retrieved on April 18, 2009. - ↑ "Fish".
*The Life Lexicon*. Stephen Silver. Retrieved on April 18, 2009. - ↑ "Gliders in Life-Like Cellular Automata". David Eppstein. Retrieved on April 18, 2009.
- ↑ http://www.njohnston.ca/2009/10/spaceship-speed-limits-in-life-like-cellular-automata/
- ↑ Alexey Nigin (7 Mar 2016). "New Spaceship Speed in Conway’s Game of Life". Retrieved on 11 Jun 2016.
- ↑ Tim Coe. "c/5 Orthogonal spaceship". Paul's Page of Conway's Life Miscellany. Retrieved on April 18, 2009.
- ↑ David Bell. "New c/5 spaceship". Paul's Page of Conway's Life Miscellany. Retrieved on April 18, 2009.
- ↑ David Eppstein. "Searching for Spaceships (PDF)". Retrieved on April 18, 2009.
- ↑ Adam P. Goucher (May 19, 2010). "Oblique Life spaceship created".
*Game of Life News*. Retrieved on May 21, 2010.