Historically the word “atom” in modern physics and chemistry was referred to the wrong object, during the revival of science in the seventeenth century, since the smallest particles belonging to what is called a chemical element are still rather complicated systems of smaller units. These smaller units are nowadays called elementary particles, and it is obvious that if anything in modern physics should be compared with the atoms of Democritus it should be the elementary particles like proton, neutron, electron, meson.
Democritus was well aware of the fact that if the atoms should, by their motion and arrangement, explain the properties of matter – color, smell, taste – they cannot themselves have these properties. Therefore, he has deprived the atom of these qualities and his atom is thus a rather abstract piece of matter. But Democritus has left to the atom the quality of “being,” of extension in space, of shape and motion. He has left these qualities because it would have been difficult to speak about the atom at all if such qualities had been taken away from it.
On the other hand, this implies that his concept of the atom cannot explain geometry, extension in space or existence, because it cannot reduce them to something more fundamental. The modern view of the elementary particle with regard to this point seems more consistent and more radical. Let us discuss the question: What is a elementary particle? We say, for instance, simply “a neutron” but we can give no well-defined picture and what we mean by the word. We can use several pictures and describe it once as a particle, once as a wave and once as a wave packet. But we know that none of these descriptions is accurate. Certainly the neutron has no color, no smell, no taste. In this respect it resembles the atom of Greek philosophy.
Werner Heisenberg, Physics and Philosophy, 2nd edn. (Harper Perennial: 2007) pp. 43-44