  The quantum speed limit (QSL), or the energy-time uncertainty relation,
describes the fundamental maximum rate for quantum time evolution and has been
regarded as being unique in quantum mechanics. In this study, we obtain a
classical speed limit corresponding to the QSL using the Hilbert space for the
classical Liouville equation. Thus, classical mechanics has a fundamental speed
limit, and QSL is not a purely quantum phenomenon but a universal dynamical
property of the Hilbert space. Furthermore, we obtain similar speed limits for
the imaginary-time Schroedinger equations such as the master equation.
