Spinors and SU(2)

Two helices traced over θ from 0 to 4π. The upper one advances its phase as φ = θ and closes twice, the lower one as φ = θ / 2 and closes once, which is the half angle a spinor carries under SU(2). Beads mark θ = 0, 2π and 4π, and at 2π the spinor bead sits on the opposite side of its axis from where it started, since ψ(2π) = -ψ(0). Ink weight separates the near half of each coil from the far half.