Limits on the Variability ofGUsing Binary-Pulsar Data

One of the few experimental handles on unified theories of gravity with other interactions comes from possible time variation of coupling constants over the Hubble time: H₀^_^-1(7.67×10^-11 yr^-1)^-1. We present a new theory-independent estimate (consistent with zero) of the time variation of Newton's gravitational constant derived from the timing of the binary pulsar PSR 1913+16: ̇ \.G₀G₀=(1.0±2.3)×10^-11 yr^-1. We anticipate that this estimate will become sharper as more data are acquired.