 Epicurus’ view of the motion of atoms also differs from Democritus’. Rather than talking of a motion towards the center of a given cosmos, possibly created by the cosmic vortex, Epicurus grants to atoms an innate tendency to downward motion through the infinite cosmos. The downward direction is simply the original direction of atomic fall. This may be in response to Aristotelian criticisms that Democritus does not show why atomic motion exists, merely saying that it is eternal and that it is perpetuated by collisions. Moreover, although this is not attested in the surviving writings of Epicurus, authoritative later sources attribute to him the idea that it belongs to the nature of atoms occasionally to exhibit a slight, otherwise uncaused swerve from their downward path. This is thought to explain why atoms have from infinite time entered into collisions instead of falling in parallel paths: it is also said, by Lucretius, to enter into the account of action and responsibility. Scholars have proposed a number of alternative interpretations as to how this is thought to work.