Spaceship: Difference between revisions
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==Spaceship Speed== | ==Spaceship Speed== | ||
{{main|Speed}} | {{main|Speed}} | ||
The speed of a spaceship is the | The speed of a spaceship is the number of cells that the pattern moves during its period. 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 a speed of 2c/5. All known spaceships in life travel either orthogonally (displacement in only the x or y direction) or diagonally (equal displacement in both the x and y directions) at one of the twelve known speeds; however spaceships traveling in other directions and at different speeds have been constructed in other two dimensional cellular automata<ref>{{cite web|url=http://fano.ics.uci.edu/ca/ |title=Gliders in Life-Like Cellular Automata |publisher=David Eppstein|accessdate=April 18, 2009}}</ref>, and it is known that [[Conway's Game of Life|Life]] has spaceships that travel in all rational directions at arbitrarily slow speeds (see [[universal constructor]]). | ||
==History== | ==History== | ||
Revision as of 12:17, 18 April 2009
A spaceship (much less commonly referred to as a glider[1] or a fish[2]) is a finite pattern that returns to its initial state after a number of generations (known as its period) but in a different location.
Spaceship Speed
- Main article: Speed
The speed of a spaceship is the number of cells that the pattern moves during its period. 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 a speed of 2c/5. All known spaceships in life travel either orthogonally (displacement in only the x or y direction) or diagonally (equal displacement in both the x and y directions) at one of the twelve known speeds; however spaceships traveling in other directions and at different speeds have been constructed in other two dimensional cellular automata[3], and it is known that Life has spaceships that travel in all rational directions at arbitrarily slow speeds (see universal constructor).
History
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 the known c/2 spaceships. Significant advances in spaceship technology came when, in 1989, Dean Hickerson began using automated searches to find spaceships. These searches searches found orthogonal spaceships with speeds of c/3 c/4 and 2c/5, and also the first spaceship to move at the speed of c/4 diagonally other than the glider, dubbed the big glider. Hickerson also found a way to combine switch engines to create the first diagonal c/12 spaceship. The next new spaceship speed to be discovered was the orthogonal c/5 snail, found by Tim Coe in 1996, with a search program he had designed that could split tasks between multiple CPUs[4].
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See also
Notes
- ↑ Glider the Life Lexicon
- ↑ Fish the Life Lexicon
- ↑ "Gliders in Life-Like Cellular Automata". David Eppstein. Retrieved on April 18, 2009.
- ↑ Tim Coe, "c/5 Orthogonal spaceship" Paul's Page of Conway's Life Miscellany
External links
- Spaceship at the Life Lexicon
- Gliders in Life-Like Cellular Automata, a database maintained by David Eppstein.