clinamen

is the small, unpredictable move that atoms make when falling otherwise straight through the void (like rain) leading to collisions and thus to nature.

When atoms move straight down through the void by their own weight, they deflect a bit in space at a quite uncertain time and in uncertain places, just enough that you could say that their motion has changed. But if they were not in the habit of swerving, they would all fall straight down through the depths of the void, like drops of rain, and no collision would occur, nor would any blow be produced among the atoms. In that case, nature would never have produced anything.[1]'

clinamen, n.Definitions

clinamen