Diffusion Limited Aggregation

When this program runs, particles drift in towards the center of the grid from random directions. When they hit another particle, they stick, building up a clump of particles.

What do you think the clump will look like? Try it and see.

This kind of clumping process is called "Diffusion Limited Aggregation", because the random movement of the particles coming in is called "diffusion". It is how particles in gases and liguids move (though the particles in this program move more directly than in real diffusion, so that you don't have to wait too long for particles to hit the clump and stick). Diffusion Limited Aggregation is believed to be involved in some kinds of mineral formations.

You can press the "run/reset" button to clear the clump and start again.

Reference: Ball, P. (1999) The Self-Made Tapestry: Pattern Formation in Nature. Oxford: Oxford University Press, Ch. 5.