Light-Cone Spreading of Perturbations and the Butterfly Effect in a Classical Spin Chain

We find that the effects of a localized perturbation in a chaotic classical many-body system---the classical Heisenberg chain at infinite temperature--spread ballistically with a finite speed even when the local spin dynamics is diffusive. We study two complementary aspects of this butterfly effect: the rapid growth of the perturbation, and its simultaneous ballistic (light-cone) spread, as characterized by the Lyapunov exponents and the...