The gliders can react with each other in many different ways; a large number of the reactions cleanly destroy both gliders leaving nothing. Many of the remaining reactions cleanly create some common objects, and so are used as the first steps in glider syntheses or as part of constructing interesting objects using rakes. Only a small number of collisions can be considered dirty due to creating multiple objects or a mess.
Here is a list of the possible results along with how many different ways they can occur (ignoring reflections and rotations).
|Lumps of muck||1||0|
|Four skewed blocks||0||1|
The messiest of the two-glider collisions in the "dirty" category is 2-glider mess.
|All 71 distinct 2-glider collisions, arranged by what they synthesize in a pattern constructed by Jason Summers|
(click above to open LifeViewer)
RLE: here Plaintext: here
In 1973, Everett Boyer et al. proposed a classification scheme for 90-degree two-glider collisions. By considering the delay and parity of separation, a two-glider collision is labelled with a number and a plus/minus sign. For instance, in the collision that gives a bi-block, the paths of two gliders are separated by an odd number of cells (the effect can be seen clearly under LifeHistory), and two gliders arrive simultaneously to the intersection point of two paths — therefore it is labelled "0-". Delaying any of the two gliders gives a "1-" reaction that synthesizes a B-heptomino. The results are tabulated below.
|Delay||Parity of separation|
|Even (+)||Odd (-)|
|0||(0+) Interchange||(0-) Bi-block|
|1||(1+) 94-tick spark||(1-) B-heptomino|
|2||(2+) Honeyfarm||(2-) Blinker|
|3||(3+) Pond||(3-) 32-tick spark|
|4||(4+) 4-tick spark||(4-) Traffic light and glider|
|5||(5+) Honeyfarm||(5-) 6-tick spark|
|6||(6+) Honeyfarm||(6-) 13-tick spark|
|7||(7+) Teardrop||(7-) 10-tick spark|
|8||(8+) Blinker, loaf, block and tub||(8-) 8-tick spark|
|9||(9+) Eater 1||(9-) Lumps of muck|
|10||(10+) Block||(10-) Blinker|
|11||(11+) 4-tick spark||(11-) Traffic light|
|12||(12+) Beehive||(12-) Block|
|13||(13+) Two-glider mess||(13-) 11-tick spark|
|14||(14+) Half-blockade||(14-) 13-tick spark|
|15||(15+) Pi-heptomino||(15-) 4-tick spark|
|16||(16+) Pi-heptomino||(16-) Traffic light|
|17||(17+) Block||(17-) Glider (90-degree kickback)|
|18||(18+) Blinker and loaf||(18-) Blinker and loaf|
|19||No reaction onwards||No reaction onwards|
- The direction requirement is a necessary but not sufficient condition for the 2-glider collision to be valid. For two gliders in the same direction, they either do not interact forever, or collapse in at most 4 ticks due to being very close. In the latter case, the gliders cannot come from infinity and this "collision" is deemed invalid. Glider syntheses should avoid such glider pairs.
- Bob Shemyakin (February 15, 2015). Errors of glider synthesis (discussion thread) at the ConwayLife.com forums
- Robert Wainwright (September 1972). "Lifeline Volume 5". Lifeline.
- Dave Greene (January 29, 2005). "71 Glider Collisions". Game of Life News. Retrieved on April 25, 2020.
- Robert Wainwright (September 1973). "Lifeline Volume 11". Lifeline page 10.