Stable reflector
A stable reflector is any arrangement of still lifes that can absorb a glider, releasing one or more gliders and restoring itself in the process. The first reflectors were found by Paul Callahan in 1996. There are several distinct categories of stable reflector:
- 'Callahan' reflector - A reflector that temporarily creates an unwanted still-life and later destroys it.
- 'Buckingham' reflector - A reflector that temporarily destroys a necessary still-life and later reconstructs it.
- Direct reflector - A reflector that does not contain a Herschel track.
Records
Ideally, stable reflectors should be as small and fast as possible. Here are the current contenders:
- Smallest 90° reflector: [1]
- Fastest 90° reflector: [2]
- Smallest 180° reflector: rectifier
- Fastest 90° reflector: rectifier
The third record is debatable, since the boojum reflector has a smaller bounding box across all phases; the rectifier has the smallest quiescent configuration. The terms 'active' and 'passive' bounding box should be used to avoid confusion.
The $100 prize
The first record, unbroken since 1998, fits inside a 81*64 bounding box. Dave Greene has offered two $50 prizes:
- Find a stable glider reflector that fits inside a 50*50 bounding box.
- Find a stable glider reflector that fits inside a 35*35 bounding box.
Solving the second challenge before the first challenge has been solved would win both prizes simultaneously.
Staged-recovery systems
The staged-recovery system was invented by Dave Greene, when he incorporated it into his highway robber and stable Heisenburp patterns. In 2009, Adam P. Goucher built two 'Callahan' reflectors using a staged-recovery system.