To understand the word QUANTUM, think of a trombone. Blow into the mouthpiece, and move the slide out while you're blowing. The pitch goes smoothly down - not in steps, but continuously. You slide not only through all the notes on the scale but through all possible pitches in between. But hold the slide in one place and blow into the mouthpiece. You get one note. Pinch the lips tighter, and the note suddenly jumps a few steps upward. You can't play the notes in between: The laws of physics (in this case, the mathematics of a vibrating column of air) prevent it. You're either on one pitch or the other. The world of classical physics resembles the first case. Nearly everything we see appears to have smooth gradations: Colors shade into one another, temperature falls evenly overnight, and even people come in every possible size between short and tall. That's not the case at what physicists call ``the quantum level.'' Down here, at the subatomic scale, distances are measured in units of less than the diameter of an atom (10-8, or 1 1-hundred-millionth centimeters). And here the transitions between the various states of energy in the atom don't occur smoothly. They change only in jumps, as though the energy came in tiny unbreakable packets.
Hence the word QUANTUM, meaning a QUANTITY or a DISCRETE AMOUNT. And hence our metaphor a QUANTUM LEAP - meaning a sudden jump from one level to another (of knowledge, say, or social consciousness) without the usual process of climbing through the stages in between.