Democratus (c. 460–371 B.C.E.)—a student of Leucippus (fl. 450–420) who opposed Parmenides and Zeno (c. 490–c. 430 B.C.E.) by saying that empty space is real—said that existence is made up of a very large number of things that cannot be cut apart. He called these things a-tomos or atoms. Atoms are in motion within infinite space. They collide, and their movement creates a vortex; out of that, different kinds of things result. The only real qualities that we can perceive are size and shape, because the atoms have that, but everything else available to the senses is an illusion. Democratus was the originator of what became the modern theory of atoms.