Zitterbewegung — The Trembling Dirac Electron

A free relativistic electron never quite moves in a straight line. Schrödinger showed in 1930 that solutions of the Dirac equation contain a rapid, small-amplitude trembling motion — Zitterbewegung — caused by quantum interference between the electron's positive- and negative-energy components. This simulation evolves an exact 2×2 spinor state under the free Dirac Hamiltonian in closed form (no numerical integration of the wavefunction, so the quantum evolution is exact at every frame) and integrates the resulting velocity expectation value to trace the electron's real trembling trajectory in 3D, alongside the straight classical drift it would follow with no negative-energy admixture. Adjust mass, momentum and the negative-energy admixture live to see how each reshapes the amplitude and frequency of the trembling.