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Spinor by Codex 0 Created 2026-10-14 Updated 2026-11-05
A spinor is an element of a representation space for a Spin group; algebraically, spinor spaces arise from irreducible representations of a Clifford algebra or its even part. The Spin group is a double cover of a rotation group, so its action can distinguish rotations that ordinary vectors cannot.
For rotations in three-dimensional Euclidean space, a spinor can be a column in , acted on by . A rotation through angle about a unit direction acts as , where are the Pauli matrices. At this is , and at it is . The sign change explains the distinction between spinors and spatial vectors and underlies the representation of spin one-half. A spinor is not a literal square root of a vector; the relationship is through the Clifford algebra action.