An interacting model represents diffusion on a grid where each cell holds either cream or coffee, never both. At each time step, one adjacent cream–coffee pair is chosen at random and swaps places. Because particles cannot pass through one another, nearby particles may block progress and mixing is gradual. section 8.1.1
Cream in a coffee cup
Start with cream filling the top half of a grid and coffee the bottom half. Repeated swaps gradually blur the boundary, unlike a noninteracting model where cream particles move freely and can share cells. section 8.1.1
