An upper limit to the secular variation of the gravitational constant from white dwarf stars

A variation of the gravitational constant over cosmological ages modifies the main sequence lifetimes and white dwarf cooling ages. Using an state-of-the-art stellar evolutionary code we compute the effects of a secularly varying G on the main sequence ages and, employing white dwarf cooling ages computed taking into account the effects of a running G, we place constraints on the rate of variation of Newton's constant. This is done using the white dwarf luminosity function and the distance of the well studied open Galactic cluster NGC 6791. We derive an upper bound G'/G ~ -1.8 10^{-12} 1/yr. This upper limit for the secular variation of the gravitational constant compares favorably with those obtained using other stellar evolutionary properties, and can be easily improved if deep images of the cluster allow to obtain an improved white dwarf luminosity function.Comment: 15 pages, 4 figures, accepted for publication in JCA

Resource Letter PTG-1: Precision Tests of Gravity

This resource letter provides an introduction to some of the main current topics in experimental tests of general relativity as well as to some of the historical literature. It is intended to serve as a guide to the field for upper-division undergraduate and graduate students, both theoretical and experimental, and for workers in other fields of physics who wish learn about experimental gravity. The topics covered include alternative theories of gravity, tests of the principle of equivalence, solar-system and binary-pulsar tests, searches for new physics in gravitational arenas, and tests of gravity in new regimes, involving astrophysics and gravitational radiation.Comment: 9 pages; submitted to American Journal of Physic

An independent constraint on the secular rate of variation of the gravitational constant from pulsating white dwarfs

A secular variation of the gravitational constant modifies the structure and evolutionary time scales of white dwarfs. Using an state-of-the-art stellar evolutionary code and an up-to-date pulsational code we compute the effects of a secularly varying $G$ on the pulsational properties of variable white dwarfs. Comparing the the theoretical results obtained taking into account the effects of a running $G$ with the observed periods and measured rates of change of the periods of two well studied pulsating white dwarfs, G117--B15A and R548, we place constraints on the rate of variation of Newton's constant. We derive an upper bound $\dot G/G\sim -1.8\times 10^{-10}$ yr$^{-1}$ using the variable white dwarf G117--B15A, and $\dot G/G\sim -1.3\times 10^{-10}$ yr$^{-1}$ using R548. Although these upper limits are currently less restrictive than those obtained using other techniques, they can be improved in a future measuring the rate of change of the period of massive white dwarfs.Comment: 13 pages, 4 tables, 3 figures. To be published in the Journal of Cosmology and Astroparticle Physic

The Constancy of the Constants of Nature: Updates

The current observational and experimental bounds on the time variation of the constants of nature (the fine structure constant $\alpha$, the gravitational constant $G$ and the proton-electron mass ratio $\mu=m_p/m_e$) are reviewed.Comment: 27 pages, 2 figures, to be published in Prog.Theor.Phys, ref. adde

Spherically Symmetric, Metrically Static, Isolated Systems in Quasi-Metric Gravity

The gravitational field exterior respectively interior to a spherically symmetric, isolated body made of perfect fluid is examined within the quasi-metric framework (QMF). It is required that the gravitational field is "metrically static", meaning that it is static except for the effects of the global cosmic expansion on the spatial geometry. Dynamical equations for the gravitational field are set up and an exact solution is found for the exterior part. Besides, equations of motion applying to inertial test particles moving in the exterior gravitational field are set up. By construction the gravitational field of the system is not static with respect to the cosmic expansion. This means that the radius of the source increases and that distances between circular orbits of inertial test particles increase according to the Hubble law. Moreover it is shown that if this model of an expanding gravitational field is taken to represent the gravitational field of the Sun (or isolated planetary systems), this has no serious consequences for observational aspects of planetary motion. On the contrary some observational facts of the Earth-Moon system are naturally explained within the QMF. Finally the QMF predicts different secular increases for two different gravitational coupling parameters. But such secular changes are neither present in the Newtonian limit of the quasi-metric equations of motion nor in the Newtonian limit of the quasi-metric field equations valid inside metrically static sources. Thus standard interpretations of space experiments testing the secular variation of G are explicitly theory-dependent and do not apply to the QMF.Comment: 33 pages; v2: connection changed; v3: extended and local conservation laws changed; v4: major revision; v5: accepted for publication in G&C, v6: must have non-universal gravitational coupling; v7: fully coupled theory implemented; v8: fully coupled theory abandone

Cosmic Time Variation of the Gravitational Constant

A pre-relativistic cosmological approach to electromagnetism and gravitation is explored that leads to a cosmic time variation of the fundamental constants. Space itself is supposed to have physical substance, which manifests by its permeability. The scale factors of the permeability tensor induce a time variation of the fundamental constants. Atomic radii, periods, and energy levels scale in cosmic time, which results in dispersionless redshifts without invoking a space expansion. Hubble constant and deceleration parameter are reviewed in this context. The time variation of the gravitational constant at the present epoch can be expressed in terms of these quantities. This provides a completely new way to restrain the deceleration parameter from laboratory bounds on the time variation of the gravitational constant. This variation also affects the redshift dependence of angular diameters and the surface brightness, and we study in some detail the redshift scaling of the linear sizes of radio sources. The effect of the varying constants on source counts is discussed, and an estimate on the curvature radius of the hyperbolic 3-space is inferred from the peak in the quasar distribution. The background radiation in this dispersionless, permeable space-time stays perfectly Planckian. Cosmic time is discussed in terms of atomic and gravitational clocks, as well as cosmological age dating, in particular how the age of the Universe relates to the age of the Galaxy in a permeable space-time

Constraining a possible time variation of the gravitational constant G with terrestrial nuclear laboratory data

Testing the constancy of the gravitational constant G has been a longstanding fundamental question in natural science. As first suggested by Jofr\'{e}, Reisenegger and Fern\'{a}ndez [1], Dirac's hypothesis of a decreasing gravitational constant $G$ with time due to the expansion of the Universe would induce changes in the composition of neutron stars, causing dissipation and internal heating. Eventually, neutron stars reach their quasi-stationary states where cooling due to neutrino and photon emissions balances the internal heating. The correlation of surface temperatures and radii of some old neutron stars may thus carry useful information about the changing rate of G. Using the density dependence of the nuclear symmetry energy constrained by recent terrestrial laboratory data on isospin diffusion in heavy-ion reactions at intermediate energies and the size of neutron skin in $^{208}Pb$ within the gravitochemical heating formalism, we obtain an upper limit of the relative changing rate of $|\dot{G}/G|\le4\times 10^{-12}yr^{-1}$ consistent with the best available estimates in the literature.Comment: 27 pages, 11 figures, and 2 tables. Accepted version to appear in PRC (2007