[JumpCrisscross]

> but I don’t really know the actual physics

Vastly oversimplifying: two versus three dimensions.

[rcme]

I don’t think that explains it at all. So garbage floats (more or less), so can be modeled as a 2D plane. But why do patches form? Why isn’t the garbage distributed uniformly across the plane? And why doesn’t that same mechanism apply in 3D?