 Little is known about Leucippus, while the ideas of his student Democritus—who is said to have taken over and systematized his teacher’s theory—are known from a large number of reports and fragments quoted by others. These early atomists theorized that the two fundamental and oppositely characterized constituents of the natural world are indivisible bodies—atoms—and void. The latter is described simply as nothing, or as the negation of being. Atoms were said to be intrinsically unchangeable; they can move about in the void and combine into different clusters, which give rise to the macroscopic bodies of the perceived world. Because all macroscopic objects are in fact combinations of atoms, everything in the world of our experience is transitory and subject to dissolution while the atoms themselves persist through all time.