Home › Physical Sciences & Cosmology › Quantum Mechanics › spin

spin

SPIN /spɪn/

nounC1GRE

formaltechnical

An intrinsic form of angular momentum carried by elementary particles, atoms, and nuclei, which is quantized and has no classical analogue.

Unlike the classical spin of a top, quantum 'spin' doesn't imply a physical rotation. It's an inherent quantum property, like mass or charge, that has a direction (up or down, for example) and a specific, quantized value.

The story behind the word. The word 'spin' comes from Old English spinnan, meaning 'to draw out and twist fibers into thread.' It later evolved to mean 'to rotate rapidly.' When physicists discovered this intrinsic angular momentum of particles in the 1920s, they named it 'spin' by analogy to a rotating object, even though it doesn't involve actual physical rotation in the classical sense.

Word relationships

intrinsic angular momentum: A more technical and precise description of quantum spin.

Commonly confused with

classical rotation: Classical rotation is a physical movement; quantum spin is an intrinsic, non-classical property.

Word family

spinning (adjective): rotating rapidly

Collocations

electron spin
spin up
spin down
spin state

Idioms & expressions

spin a yarn
spin out of control

Example sentences

"Electrons have an intrinsic property called spin, which can be 'up' or 'down' relative to a given axis." Explaining a fundamental particle property.
"Particle spin is crucial for understanding how atoms interact and for phenomena like entanglement." Discussing its role in quantum phenomena.
"The concept of electron spin was first proposed by George Uhlenbeck and Samuel Goudsmit in 1925 to explain certain spectral lines." A historical note.

Memory hook

Think of a tiny, invisible top that has a fixed 'SPIN' direction, either up or down, but it's not actually spinning like a toy. Intrinsic direction

When not to use

Do not confuse quantum 'spin' with literal physical rotation. While the name is evocative, the underlying physics is distinct.

Fun facts

Particles are classified as fermions (half-integer spin, like electrons) or bosons (integer spin, like photons) based on their spin.
The Pauli Exclusion Principle, which dictates that no two identical fermions can occupy the same quantum state, is directly related to electron spin.