  The atomists held that there are two fundamentally different kinds of realities composing the natural world, atoms and void.  Atoms, from the Greek adjective atomos or atomon, ‘indivisible,’ are infinite in number and various in size and shape, and perfectly solid, with no internal gaps.  They move about in an infinite void, repelling one another when they collide or combining into clusters by means of tiny hooks and barbs on their surfaces, which become entangled.  Other than changing place, they are unchangeable, ungenerated and indestructible.  All changes in the visible objects of the world of appearance are brought about by relocations of these atoms: in Aristotelian terms, the atomists reduce all change to change of place.  Macroscopic objects in the world that we experience are really clusters of these atoms; changes in the objects we see—qualitative changes or growth, say—are caused by rearrangements or additions to the atoms composing them. While the atoms are eternal, the objects compounded out of them are not.  Clusters of atoms moving in the infinite void come to form kosmoi or worlds as a result of a circular motion that gathers atoms up into a whirl, creating clusters within it (DK 68B167); these kosmoi are impermanent.  Our world and the species within it have arisen from the collision of atoms moving about in such a whirl, and will likewise disintegrate in time.