How to Estimate Energy Lost to Gravitational Waves (revised)

The energy–momentum radiated in gravitational waves by an isolated source is given by a formula of Bondi. This formula is highly non–local: the energy–momentum is not given as the integral of a well–defined local density. It has therefore been unclear whether the Bondi formula can be used to get information from gravity–wave measurements. In this note, we obtain, from local knowledge of the radiation field, a lower bound on the Bondi flux.