  In this note, we use an elementary argument to show that the existence and
unitarity of radiation fields implies asymptotic partition of energy for the
corresponding wave equation. This argument establishes the equipartition of
energy for the wave equation on scattering manifolds, asymptotically hyperbolic
manifolds, asymptotically complex hyperbolic manifolds, and the Schwarzschild
spacetime. It also establishes equipartition of energy for the energy-critical
semilinear wave equation on $\mathbb{R}^{3}$.
