Three states, one rhythmWhat every cell of the medium is doing, right now
Ready to fire
The reduced red ground. Reagent sitting below threshold, ferroin waiting. Nothing moves — but the smallest push tips it over.
The blue front
Cross the threshold and the cell oxidises — snaps blue and shoves its neighbours over the edge too. That hand-off, cell to cell, is a travelling wave.
Spent, then patient
Behind the front, each cell is refractory — it cannot fire again until the slow variable relaxes. That lag is why fronts travel outward and never bounce back.
The clock has no handsConcentration at one point of the dish, sampled live
It never settles. That is not a fault in the chemistry — it is the chemistry.
An equilibrium reaction fades to a single colour and stops. This one can't: the product of one step is the fuel of the next, so it overshoots, corrects, overshoots again — a feedback loop wound into a clock. The trace to the right is the real oxidation level at the centre of the dish above, read straight off the simulation each frame. Every rise is a blue front sweeping through; every fall is the red recovery behind it.