ZITTERBEWEGUNG
Dirac Equation — Relativistic Electron Trembling Motion
The Dirac equation predicts that a free relativistic electron does not travel in a straight line — its trajectory shows rapid oscillations called Zitterbewegung ("trembling motion"), at frequency ω_ZB = 2mc²/ℏ. This arises from interference between positive- and negative-energy components. Left: wavepacket probability density. Right: expectation value ⟨x⟩(t) showing the trembling superimposed on drift.