The Unit Life Cell

The unit Life cell is a much discussed but until recently hypothetical pattern. In his glossary, Alan Hensel defines it as "a pattern with two states, which is determined by its previous state and the previous state of its neighbors, using exactly the rules used to compute it; that is, it simulates its own universe."

It has been known for a long time that Life is a universal computer, thus proving that Life can simulate itself in some sense. Also, enough logic gates and memory units have been constructed over the years to suggest that one ought to be able to build a unit Life cell explicitly.

Well, to make a long story short, David Bell has gone ahead and done it. You can view this pattern in Java if your browser supports it, but if you really want to see the pattern in action, you are better off downloading it and watching it in one of the fast Life programs available on the main Life page.

This leaves open the question of whether a smaller, faster unit cell exists. It would be especially interesting if a unit Life cell could be found that was not composed of glider logic, but somehow worked more directly from the Life rules. Such a unit cell might be much smaller than the one below, but it is unclear how one would go about searching for it.

From: "David I. Bell"
Subject: Corrected Unit Life Cell
Date: Thu, 18 Jan 1996 21:10:17 +1100

Here is the corrected Unit Life Cell for your enjoyment. ... I am pretty sure that this new Unit Life Cell actually works. I spent one whole day calculating the results of a 3 by 4 rectangle of Cells which runs a Glider for 2 Generations. That test tried out most of the possible logic, including 3 neighbors creating a new cell, 3 neighbors keeping an old cell alive, 2 neighbors keeping a cell alive, 1 neighbor killing off a cell, and 4 neighbors killing off a cell. [The red box highlights the "pair of long boats" referred to below. -PBC]

Here are some approximate generation numbers for important events which occur during the 5760 generations which make up one Generation. Some of these events only occur if the Cell is LIVE.

0:	Current state glider starts from pair of long boats
400:	Current state glider arrives at fanout device
600:	Output gliders escape from the fanout device
900:	Missing LWSS turned into boat to hold Cell's current state
1800:	First glider arrives at the glider detector to be turned into a block
4000:	Last glider arrives at the glider detector to be turned into a block
	and the high period glider guns fire
4700:	Stream of 10 gliders starts sweep through glider detector to count
	the number of blocks in the detector
5200:	Gliders from stream react in the Life Logic circuit to calculate
	the new current state glider
5700:	New current state glider arrives back at the pair of long boats
BCNU, -dbell-
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