Is the Gravitational Constant Changing?

Abstract

The question posed by the title is not yet conclusively resolved. Nonetheless, determinations of the lunar tidal acceleration based on dynamical time scales are now in reasonable accord with one another, whether based on the transits of Mercury, ancient eclipse observations, ocean tide models, or artificial satellite observations; these give a purely tidal component of −28.8 ± 1.5 ″/cy². Lunar occultations and laser ranging now give concordant results for the total anomalous acceleration of about −22.8 ± 1.5. The difference in these results gives an acceleration of possible cosmological origin of $\dot n/n = + 3.5 \pm 1.2 \times 10^{ - 11}$ per year, which is also consistent with very preliminary planetary radar studies. If interpreted in the scalar covariant cosmology of Canuto and Hsieh, this implies that Ġ/G = (−6.9 ± 2.4) × 10⁻¹¹ per year, if measured in atomic time, but zero if measured in dynamical time. The implications for relativity and cosmology are discussed briefly in the paper, scheduled for the Astrophysical Journal issue of 1 September 1981.