We review the recently proposed light-cone quantization of the matrix model which is expected to have a critical point describing 2-d quantum gravity coupled to c = 2 matter. In the N → ∞ limit, we derive a linear Schroedinger equation for the free string spectrum. Numerical study of this equation suggests that the spectrum is tachyonic, and that the string tension diverges at the critical poin...

Using standard big-bang nucleosynthesis and present, high-precision measurements of light element abundances, we place constraints on the self-gravity of radiation pressure in the early universe. The self-gravity of pressure is strictly non-Newtonian, and thus the constraints we set are a direct test of this aspect of general relativity. Subject headings: general relativity; Friedmann equation;...

For heterogeneous reservoirs, fast, stable and accurate methods are hard to obtain. Large changes in the velocity field leads to severe time-step restrictions in explicit schemes or expensive time steps in implicit schemes. In the absence of gravity, the exact velocity field will be loop-free in the sense that there are no closed integral curves. A sequential splitting strategy with streamline ...

A quantum gravity theory which becomes renormalizable at short distances due to a spontaneous symmetry breaking of Lorentz invariance and diffeomorphism invariance is studied. A breaking of Lorentz invariance with the breaking patterns SO(3, 1) → O(3) and SO(3, 1) → O(2), describing 3 + 1 and 2 + 1 quantum gravity, respectively, is proposed. A complex time dependent Schrödinger equation (genera...

A quantum gravity theory which becomes renormalizable at short distances due to a spontaneous symmetry breaking of Lorentz invariance and diffeomorphism invariance is studied. A breaking of Lorentz invariance with the breaking patterns SO(3, 1) → O(3) and SO(3, 1) → O(2), describing 3 + 1 and 2 + 1 quantum gravity, respectively, is proposed. A complex time dependent Schrödinger equation (genera...

The strongest evidence for dark energy comes presently from geometric techniques such as the supernova distance-redshift relation. By combining the measured expansion history with the Friedmann equation one determines the energy density and its time evolution, hence the equation of state of dark energy. Because these methods rely on the Friedmann equation which has not been independently tested...

We discuss the stability of semiclassical gravity solutions with respect to small quantum corrections by considering the quantum fluctuations of the metric perturbations around the semiclassical solution. We call the attention to the role played by the symmetrized two-point quantum correlation function for the metric perturbations, which can be naturally decomposed into two separate contributio...

The problem of Stoneley waves in a non-homogeneous orthotropic elastic medium under the influence of gravity was studied recently by Abd-Alla and Ahmed [A.M. Abd-Alla, S.M. Ahmed, Stoneley waves and Rayleigh waves in a non-homogeneous orthotropic elastic medium under the influence of gravity, Appl. Math. Comput. 135 (2003) 187-200], who derived the secular equation of the wave in the implicit f...