Greek philosophers first proposed that matter was composed of tiny, indivisible particles in constant motion. However, this concept was not popular at the time, especially with Aristotle, and disappeared. Independently, ATOMIC THEORY was revived in the 19th Century. Advances in PHYSICS, especially the development of quantum mechanics, provided a satisfactory explanation for the behavior of electrons and other sub-atomic particles. An understanding of ATOMIC THEORY made possible the development of NUCLEAR FISSION and atomic weapons.
