Explainer: Quantum is the world of the super small

The public often misuses the term, but here’s what it really means

Quantum refers to the measurement and operations of particles and energy on subatomic scales. At this scale, things can appear as particles or waves and exist in more than one place at once.

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The term quantum seems to come up all the time. There’s quantum computing and a quantum internet. Quantum encryption. There’s a whole field of quantum physics. And there’s even the phrase “quantum leap.” But what does that mean? Is such a leap especially tall? What’s the big deal?

In fact, a quantum leap is amazingly small. The word quantum refers to the smallest amount of something that you can have. You can’t break a quantum of something into smaller parts. A quantum is the most basic building block.

In 1900, German physicist Max Planck came up with a revolutionary idea. It had to do with energy — in the form of heat or light — as it radiated from a source. Planck argued that this energy was quantized. By that he meant it could only be found in amounts made up of whole numbers of those smallest amounts or building blocks. A photon is a quantum of light. You can’t break a photon into smaller pieces. In other words, there’s no such thing as half a photon.

Planck went on to win the Nobel Prize in physics, the highest honor in this field. His work helped lay the foundation for quantum physics. This is an area of science that describes the behavior of particles at the smallest scales. Subatomic scales. (Subatomic is smaller than an atom.)

Still, some people use the word “quantum” to describe something surprisingly big. It’s especially true with the phrases “quantum leap” or “quantum jump.” But quantum doesn’t mean “big.” It’s the exact opposite. So, when something does undergo a quantum jump, its energy changes — but not by much.

Stephen Ornes lives in Nashville, Tenn., and his family has two rabbits, six chickens and a cat. He has written for Science News for Students since 2008 on topics including lightning, feral pigs, big bubbles and space junk.

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