I was clicking around those free PhET science simulations and then somehow landed in a bunch of old WebGL experiments. One thing kept pulling me back in: these tiny grid worlds where two invisible chemicals just diffuse and react with each other. No brains, no rules about "make a spot here." Just math. And out come spots, stripes, pulsing waves, even little mazes that look like they belong on a seashell or a zebra.
The model is called Gray-Scott. It's from the early 90s but people still play with it because the patterns feel alive. Two chemicals, U and V. U is kind of the "food." V "eats" it in a certain way. They spread at different speeds. Feed a little U in, kill off a little V, and depending on the exact rates, the whole thing organizes itself into surprising shapes.
Here's a live version running right in the page. The canvas is the petri dish. Click or drag to stir things up. Use the sliders to change how much food arrives (F) and how fast the second chemical gets removed (k). Hit the preset buttons to jump to known interesting states.
Click/drag on the canvas to add a little chaos. It keeps running until you pause it (click the canvas to toggle pause).
The simulation is running a very stripped-down version of the equations on a 200×200 grid (scaled up for the screen). Every frame it diffuses the concentrations a bit, then lets them react, then repeats. That's it. Yet the results look organic.
Alan Turing wrote about this kind of thing in 1952 — how simple chemical rules could explain why animals have spots or stripes instead of being solid colors. The Gray-Scott model is one of the cleanest ways to watch that idea come alive on a screen.
Change F or k by a tiny amount and the whole world flips from calm spots to wild pulsing rings or chaotic turbulence. Some parameter combinations make little "solitons" that travel around like lonely creatures. Others make the pattern grow like a living mold.
It's not modeling any specific animal. It's just two chemicals following local rules. The complexity emerges from the interaction + the slight difference in how fast they spread. That difference is the secret sauce.
I kept a tab open with different presets running in the background while I poked at the sliders. Every so often I'd glance over and think "that one looks like a coral reef" or "that looks like the veins on a leaf." Then I'd tweak one number and the whole thing would reorganize in a completely different direction.
There's something oddly satisfying about watching order appear from almost nothing, then watching it fall apart again when you change the rules. No goal. No winner. Just the math doing its thing.
Search for "Gray-Scott" on the web and you'll find dozens of versions, some in shaders running at 60 fps on huge grids, some that let you paint with the mouse in real time. The original papers are from the 90s but the visual toys people have made since then are everywhere.
PhET has a bunch of other reaction and diffusion sims too if you want to stay in the "play with invisible rules" corner of the internet for a while.
I don't know why this one grabbed me today. Maybe because it feels like a tiny universe that follows its own quiet logic, and all you have to do is sit there and watch what happens when you change one dial.