Amoeba

The rule

In Softology's notation 9-26/5-7,12-13,15/5/M: a live cell survives with 9 or more live neighbours, a dead cell is born with 5, 6, 7, 12, 13 or 15, and there are 5 states (three of them dying). Survival from 9 up keeps the inside of a blob alive, while births at low counts happen at its surface, so it grows outward.

What it does

From its start, a random block half the box wide and half full, it swells and then freezes. In 20 seeded runs in a 30×30×30 box, all 20 had stopped changing by generation 44, with about 78% of the box alive. The cutaway (C) and the slice view (S) show the inside.

Run Amoeba from its start →

How the rule works

• Each cell has 26 neighbours: every cell that shares a face, an edge or a corner with it (the Moore neighbourhood).
• An empty cell comes alive when 5 to 7, 12, 13 or 15 of its neighbours are alive.
• A live cell stays alive when 9 to 26 of its neighbours are alive; otherwise it starts dying: for 3 generations it fades, is not counted as a neighbour and blocks births, then the cell is empty again.
• With 5 states in all (alive, 3 dying, dead), this is a Generations rule.

Picking it in the app restarts the world from a random block in the middle of the box, 50% full and half as wide as the box. Its seed is fixed, so it is the same world every time, one still alive 40 generations later in the default 15×15×15 box; N tries another seed.

Notation

B lists the neighbour counts at which an empty cell is born, S those at which a live cell survives, and C the number of states. How to read a rule

More of Softology's rules

• 445 B4/S4/C5
• Architecture B3/S4-6
• Builder 1 B4,6,8-9/S2,6,9/C10
• Builder 2 B1/S5-7
• Clouds 1 B13-14,17-19/S13-26
• Clouds 2 B13-14/S12-26
• Coral B6-7,9,12/S5-8/C4
• Crystal Growth 1 B1,3/S0-6
• Crystal Growth 2 B1,3/S1-2/C5
• Pyroclastic B6-8/S4-7/C10
• Spiky Growth B13,17,20-26/S0-3,7-9,11-13,18,21-22,24,26/C4
• 3D Brain B4/S

All 30 rules · From 2D to 3D: why Conway's rule needs changing in 3D