Spin-1/2

<p>In <a href="/facts/Quantum_mechanics/BRc3Mzgr">quantum mechanics</a>, <a href="/facts/Spin_(physics)/4Jvp7e8P">spin</a> is an intrinsic property of all <a href="/facts/Elementary_particle/CTFDM97U">elementary particles</a>. All known <a href="/facts/Fermion/LEckdDsR">fermions</a>, the particles that constitute ordinary matter, have a spin of ⁠1/2⁠. The spin number describes how many symmetrical facets a particle has in one full rotation; a spin of ⁠1/2⁠ means that the particle must be rotated by two full <a href="/facts/Turn_(angle)/QczxAyuM">turns</a> (through 720°) before it has the same configuration as when it started.
</p><p>Particles with net spin ⁠1/2⁠ include the <a href="/facts/Proton/clCjepXP">proton</a>, <a href="/facts/Neutron/oRCM1geb">neutron</a>, <a href="/facts/Electron/L0KBo5cW">electron</a>, <a href="/facts/Neutrino/yGWVfSg2">neutrino</a>, and <a href="/facts/Quarks/hwuuVkV5">quarks</a>. The dynamics of spin-⁠1/2⁠ objects cannot be accurately described using <a href="/facts/Classical_physics/gGnINVPE">classical physics</a>; they are among the simplest systems whose description requires <a href="/facts/Quantum_mechanics/BRc3Mzgr">quantum mechanics</a>. As such, the study of the behavior of spin-⁠1/2⁠ systems forms a central part of <a href="/facts/Quantum_mechanics/BRc3Mzgr">quantum mechanics</a>.
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Spin-1/2 open-in-new

Spin-1/2