The problem of motion of bodies in general relativity dates back to the early days of the theory. Initially considered in the slow-motion approximation, the derivation of the equations of motion to first post-Newtonian order is due to Einstein, Infeld and Hoffman, with much more precise approximations obtained since. A natural question considered in this connection is whether there exist solutions which are periodic in time–the problem of eternal return. For asymptotically simple space-times, we show that this is not possible, at least near infinity. We relate this to the problem of reconstructing a solution of the Einstein equations from knowledge of the radiation it has emitted towards infinity. Joint work with V. Schlue, and (partly) A. Shao.