In this article we study the pointwise decay properties of solutions to the
wave equation on a class of nonstationary asymptotically flat backgrounds in
three space dimensions. Under the assumption that uniform energy bounds and a
weak form of local energy decay hold forward in time we establish a $t^{-3}$
local uniform decay rate (Price's law \cite{MR0376103}) for linear waves. As a
corollary, we also prove Price's law for certain small perturbations of the
Kerr metric.
This result was previously established by the second author in \cite{Tat} on
stationary backgrounds. The present work was motivated by the problem of
nonlinear stability of the Kerr/Schwarzschild solutions for the vacuum Einstein
equations, which seems to require a more robust approach to proving linear
decay estimates.