I found this replicator in rule B368/S12578 in 1999. It replicates
itself every 13 generations, on a one-dimensional 4-unit grid.
The same replicator works also in B3678/S12578.
Arbitrarily high period oscillators can be made by terminating a row of
replicators by still lifes in any of several ways.
This rule has
known spaceships, including a small c/8 diagonal glider.
As I discovered, two replicator-based oscillators can crash to form a
glider and some random debris, which can be removed by more replicators.
The following cleaned-up versions of this glider gun idea
were made by Dean Hickerson.
It would be of interest to find puffers or spaceships based on this
replicator, that move at speed 4c/13.
However, much slower spaceships may also exist:
Dean Hickerson has found "push"
reactions in which a set of replicators pushes or pulls a still life by
twelve units. It should be possible to set up
arbitrarily-slow replicator-based spaceships in which a set of
replicators periodically forms a push reaction at the front end and a
pull reaction at the other end. However, the likely size of these
things is so huge
(exponential in the period) that no explicit example has been made.
Cellular Automata --
D. Eppstein --
UCI Inf. & Comp. Sci.