Stephen Silver's 81x62 stable reflector
discovered on 6 November 1998.
Uses a Herschel conduit to repair
an imperfect two-beehive reflector
found earlier by Paul Callahan.
Ever since Paul Callahan discovered the first stable reflector in 1996, people have continually searched for increasingly smaller reflectors. This has been partially successful
, as in the two years that followed the area of stable reflectors decreased by approximately two orders of magnitude. The smallest 90-degree reflector to date was found by Stephen Silver, and has a bounding box of 81*62.
The problem is this: Silver's reflector was found over a decade ago, in 1998, and no-one has managed to beat this record. Dave Greene discovered a compact 180-degree reflector, which he dubbed the boojum reflector, in 2001. Recently Adam P. Goucher discovered a slightly smaller and much faster 180-degree reflector (the Rectifier). However, these 180-degree reflectors bring us no closer to finding a compact 90-degree reflector.
Shortly after discovering the boojum reflector, Dave Greene recycled half of the prize money into two new prizes. Each prize is $50 USD, and both are for small 90-degree stable reflectors. The first prize is for the first 90-degree reflector to fit into a 50*50 box; the second is for accomplishing this feat in a 35*35 box.
All 90-degree stable reflectors so far comprise a Herschel track, where an active object is perturbed through a series of conduits to repair the reflector. However, this method can only yield a certain level of compactness; to achieve smaller reflectors one needs to consider alternative approaches. The boojum reflector and rectifier are such reflectors, as neither of them contains a Herschel track.
The search for a 90-degree microreflector, or Snark, has not proved successful. However, such a pattern may just be on the horizon, as increasingly promising results have been found. The closest result came from a member of the
conwaylife.com forums, MikeP, who discovered a reflector whose initial state differs from its final state in just two cells
! This was based on a discovery by Dieter Leithner last millennium, but restores the block in a completely unrelated (but equivalent) way. This suggests that there is a huge space of similar reactions out there, amongst which there might be the elusive 90-degree microreflector.