Quantum mechanics views subatomic particles as “tendencies to exist” or “tendencies to happen.” How strong these tendencies are is expressed in terms of probabilities. A subatomic particle is a “quantum,” which means a quantity of something. What that something is, however, is a matter of speculation. Many physicists feel that it is not meaningful even to pose the question. It may be that the search for the ultimate “stuff” of the universe is a crusade for an illusion. At the subatomic level, mass and energy change unceasingly into each other.
