Spinors and SU(2)

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