Spiinid

Spiinid is the Estonian plural form of spin, a fundamental property in quantum mechanics that describes the intrinsic angular momentum carried by elementary particles and certain composite systems. Unlike classical rotation, spiin is not a motion in space but an intrinsic degree of freedom that can be measured along a chosen direction.

Spin is quantized. Each particle has a spin quantum number s, with projections m_s taking values from -s to +s in integer steps. Common cases include electrons, protons, and neutrons with s = 1/2; photons with s = 1; and higher-spin particles in hadrons and nuclei.

The concept is tested by experiments such as Stern-Gerlach, which reveal discrete spin states. The simplest case, spin-1/2, is described by two-component spinors and the Pauli matrices; higher spins use larger mathematical representations.

Spin underpins quantum statistics: half-integer spins are fermions that obey the Pauli exclusion principle, while integer spins are bosons. The spin-statistics connection is central to quantum field theory.

Applications range from medical imaging (MRI, NMR) and electron-spin resonance to spintronics and quantum information processing, where spin states serve as qubits. In particle physics, spins of quarks, leptons, and gauge bosons determine interaction properties.

Historically, electron spin was proposed by Goudsmit and Uhlenbeck (1925) and confirmed experimentally; Stern and Gerlach demonstrated spin quantization in 1922.