A new class of ideal clocks

We have found a new class of ideal clocks within general relativity. They are self-gravitating systems such as rotating stars, rotating black holes, and binary star systems. The gravitational red shift of the observed period of rotation of such clocks in a given, weak external gravitational field is shown to be the same as that of an ideal atomic clock. Because the clocks have structure and dynamics determined by gravitational interactions, the full nonlinear machinery of general relativity must be used. This result is important for the binary pulsar PSR 1913+16, where the gravitational red shift of the pulsar's frequency caused by the companion's gravitational field is an observable effect.Supported in part by the National Science Foundation Grant Nos. PHY81-15800 and PHY83-13545.This essay received the third award from the Gravity Research Foundation for 1984-Ed.