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How Did "Quantum" Come to Mean "Really Big"?
Verizon offers "Even faster FiOS Quantum Internet" speeds. Duracell has a new Quantum alkaline battery. James Bond had his Quantum of Solace. Any number of companies have "quantum" in their names as well.
The implication is that "quantum" is something big and powerful, with a hint of science behind it.
That's a fairly recent development. As a noun, for most of its linguistic life it has meant "something that has quantity"; as an adjective, its common use today, it's meant merely "some measurable amount," with the, um, quantity of that amount unspecified.
The first English use of "quantum," which appeared in 1567, was philosophy-related, according to The Oxford English Dictionary. A legal use as a "quantity of money" came about 50 years later. It was used in 1649 to mean simply "share" or "allotment," as in "Poverty is her portion, and her quantum is but food and raiment."
"Quantum" passed into physics in 1870, the OED says, in a now unused sense of the "quantity of electric fluid present in an electrically neutral body." "Quantum theory" came along early in the 20th century, courtesy of both Max Planck and Albert Einstein, the OED says. It's a "theory of matter and energy based on the concept of quanta," or the idea that light contains many small but measurable bits of energy. (Though Einstein used "quanta" as the plural in his theories, a more commercial plural is "quantums.")
Duracell touts its battery as "a quantum leap in battery power." That expression began life as a "quantum jump" in 1924, adding "quantum leap" in 1932. In physics, both originally meant merely an abrupt transition, as a "quantum" of electromagnetic energy was absorbed or released. And for a time, a "quantum leap" meant a very small, discrete amount, according to the OED.
The TV program Quantum Leap, from 1989-93, where Scott Bakula played a scientist (sometimes described as a "quantum" physicist), had it exactly right: Bakula could travel through time (the abrupt-shift sense of "quantum leap"), but could travel back only a short period to inhabit the body of a specific person (the small, discrete sense).
The first use of "quantum leap" to mean "really big" was in 1956, the OED says, in a discussion of the US-Soviet balance of power in a nuclear postwar world, where a writer described "The enormous multiplication of power, the 'quantum leap' to a new order of magnitude of destruction."
The use of "quantum" in English took a "quantum leap" after 1916, no doubt because of Einstein and Planck, according to a Google Ngrams graph charting mentions of "quantum" in books.
Webster's New World College Dictionary had no definition for "quantum leap" or "quantum jump" in the 1964 printing of its first edition; by the 1982 printing of the second edition, the terms had been added, with a definition of "any sudden and extensive change or advance, as in a program or policy."
Though using "quantum leap" to mean "big jump" is fully idiomatic, it's best to avoid using just plain "quantum" to mean "huge" (especially if addressing a physicist). Most dictionaries still define it as simply "an amount." It's only the hyperbole that gives it mass quantity.