Analysis of 10 years of high-precision timing data on the millisecond pulsar PSR J0437 4715 has resulted in a model-independent kinematic distance based on an apparent orbital period derivative, Ṗb, determined at the 1.5% level of precision (Dk 1⁄4 157:0 2:4 pc), making it one of the most accurate stellar distance estimates published to date. The discrepancy between this measurement and a previ...

The BIPM is undertaking a determination of the Newtonian gravitational constant, G using a torsion balance with a thin, heavily loaded strip as the suspension element. This apparatus uses four 1.2 kg test masses and four 15.5 kg source masses to produce a gravitational torque of 2× 10−8 N m. A preliminary determination of G has been made with a relative standard uncertainty of about 1.7× 10−3, ...

ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test General Relativity with an improvement in sensitivity of over 3 orders of magnitude, improving our understanding of gravity and aiding the development of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and our knowledge of th...

We investigate the effect of possible a-priori “imprinting” effects of general relativity itself on satellite/spaceraft-based tests of it. We deal with some performed or proposed time-delay ranging experiments in the Sun’s gravitational field, and with the attempts to measure the Lense-Thirring effect with the LAGEOS satellites orbiting the Earth. It turns out that the “imprint” of general rela...

There are a number of approaches to testing General Relativity (GR) on linear scales using parameterized frameworks for modifying cosmological perturbation theory. It is sometimes assumed that the details of any given parameterization are unimportant if one uses it as a diagnostic for deviations from GR. In this brief report we argue that this is not necessarily so. First we show that adopting ...

We study the effect of dissipation on the density profile of a one-dimensonal gas that is subject to gravity. The gas is in thermal equilibrium at temperature T with a heat reservoir at the bottom wall. Perturbative analysis of the Boltzmann equation reveals that the correction due to dissipation resulting from inelastic collisions is positive for 0 ≤ z < zc and negative for z > zc with z the v...

In a recent paper, a cosmological model based on El Naschie E infinity cantorian spacetime was presented [1]. In that work it was claimed that the present accelerated expansion of the Universe can be obtained as the effect of a scaling law on newtonian cosmology with a certain time dependent gravitational constant (G). In the present work we show that it may be problematic to explain the presen...

We consider open supermembranes in an eleven dimensional background. We show that, in a flat space-time, the world-volume action is kappa-symmetric and has global space-time supersymmetry if space-time has even dimensional topo-logical defects where the membrane can end. An example of such topological defects is provided by the space-time with boundaries considered by Horava and Witten. In that...

We study evolution of a flat Friedmann-Robertson Walker universe filled with a bulk viscous cosmological fluid in a higher derivative theory of gravity in the presence of time varying gravitational and cosmological constant. Cosmological models admitting both power-law and exponential expansions are explored here in the presence of imperfect fluid described by full Israel and Stewart theory. We...

Motivated by the possibility that the fundamental “constants” of nature could vary with time, this paper considers the long term evolution of white dwarf stars under the combined action of proton decay and variations in the gravitational constant. White dwarfs are thus used as a theoretical laboratory to study the effects of possible time variations, especially their implications for the future...