Once there, it is hard for them to fall back down, because the space below is filled by smaller beads. Or vibrate a box full of a dozen layers of beads, and at the right range and rate of vibration, the wave-marked surface layer is decorated by little standing jets of beads in regular array. Frictional grain motions hug walls and only grudgingly spread. The inescapable loss of energy on rebound induces neighboring grains to cluster after rather few collisions. The unexpected order that the strange sandpiles show at our scale comes from the external energy fed in to meet losses all but absent among real atoms.
Available energy is always capable of partial conversion into new order.
Just what that order will be may indeed have no single general answer. Surprises will continue, as each rich new system sports its own wonders. We owe the simplicities of mixing to quantum laws. They hold for granular fountains and landslides, too, but when each rubbing grain holds a few thousand trillion atoms to share collisional energy, atomic simplicity is long delayed.