Limits on the Variability of $G$ Using 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: $H_0^{}{}_{}{}^{-1\mathrm{}}\simeq {(7.67\mathrm{}\times {10}^{-11\mathrm{}} {\mathrm{yr}}^{-1\mathrm{}})}^{-1\mathrm{}}$. 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: $\frac{{\dot{G}}_0}{G_0}=(1.0\mathrm{}\pm 2.3)\times {10}^{-11\mathrm{}}$ ${\mathrm{yr}}^{-1\mathrm{}}$. We anticipate that this estimate will become sharper as more data are acquired.