Prairie on Fire
B34/S345/6 — a spreading front with a long cooling trail
A six-state rule whose fronts spread outwards and leave a long cooling trail behind them, like fire moving through dry grass.
How it works
In plain English, before the notation
Six states means a cell that stops firing takes four steps to become available again. That long recovery keeps the region behind a front unavailable for a while, so fronts sweep outwards and leave broad banded trails rather than thin lines. The overall effect is close to fire moving through dry grass: it spreads, it does not come back over ground it has already burned, and it takes time before that ground can burn again.
Watch a front sweep and leave banding
- Open Presets and load "Prairie on Fire", then press Play.
- Follow the bright leading edge and count the bands of colour behind it — there should be four, one for each cooling state.
- Pause and use the Eraser to clear a firebreak ahead of the front, then resume.
Starting configurations
Loads straight into the simulatorTry any rule
The catalogue covers a few dozen rules. Here you can run any of the 262,144 two-state grid rules, or any of the 256 one-dimensional rules, including ones nobody has written up.
Well-known rules
Where it came from
Another rule from the MCell Generations collection. Rules with long cooling periods are the ones most often used to illustrate why the number of states matters as much as the birth and survival sets.
The rule, precisely
What each cell looks at
The 8 cells touching it, including diagonals (the Moore neighbourhood)
What a cell can be
Six states: 0 = ready, 1 = firing, 2 through 5 = cooling
The update
if state = 0 and (firing neighbours) in {3,4} then 1; if state = 1 then 1 when firing neighbours in {3,4,5}, else 2; if state in {2,3,4} then state + 1; if state = 5 then 0
B34/S345/6: Birth on 3 or 4 firing neighbours, Survival on 3 to 5, and 6 states in total. The final number in a Generations rule string is always the total state count, including ready and firing.
Fronts and refractory shadows
The extended cooling period dominates the behaviour:
- Activity organises into fronts that sweep outwards, leaving four distinct bands of cooling cells behind them.
- A front cannot re-enter its own trail until the cooling has finished, so it keeps moving away from where it started.
- Where two fronts meet, both usually stop, because each runs into the other’s cooling shadow.
- The rule is slower to reach a steady state than the three- and four-state rules in this family.
Not studied for computation
This rule is used to demonstrate the effect of state count, not as a substrate for building things.
Spreading fronts with recovery
The structure — susceptible, active, then a period of immunity before becoming susceptible again — is the same one used in compartmental epidemic models and in simple fire-spread models. The correspondence is structural; nothing here is calibrated against real data.
Things to try
- Reduce Speed to 10 fps so the four cooling bands are distinguishable.
- Draw a solid line of cooling cells across the grid as a firebreak and see whether a front can get past it.
- Compare with Brian’s Brain, where the cooling period is a single step, to see how much the state count changes.