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Gravitational field
About: Gravitational field is a research topic. Over the lifetime, 17951 publications have been published within this topic receiving 351335 citations.
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TL;DR: In this paper, it was shown that generic Ricci-flat manifolds do not solve the modified equations, unless in addition the manifolds are Kahler (2 N -dimensional manifolds of SU( N ) holonomy).
982 citations
TL;DR: In this article, the authors used a neutron interferometer to observe the quantum-mechanical phase shift of neutrons caused by their interaction with Earth's gravitational field, which is known as the Earth's magnetic field.
Abstract: We have used a neutron interferometer to observe the quantum-mechanical phase shift of neutrons caused by their interaction with Earth's gravitational field.
978 citations
TL;DR: It is found that the nonlinearity of Einstein gravity induces the higher multipole modes even if only a quadrupole mode exists initially.
Abstract: We perform numerical simulations of a three-dimensional (3D) time evolution of pure gravitational waves. We use a conformally flat and K=0 initial condition for the evolution of the spacetime. We adopt several slicing conditions to check whether a long time integration is possible in those conditions. For the case in which the amplitude of the gravitational waves is low, a long time integration is possible by using the harmonic slice and the maximal slice, while in the geodesic slice (\ensuremath{\alpha}=1) it is not possible. As in the axisymmetric case and also in the 3D case, gravitational waves with a sufficiently high amplitude collapse by their self-gravity and their final fates seem to be as black holes. In this case, the singularity avoidance property of the harmonic slice seems weak, so that it may be inappropriate for the formation problems of the black hole. By means of the gauge-invariant wave extraction technique we compute the waveform of the gravitational waves at an outer region. We find that the nonlinearity of Einstein gravity induces the higher multipole modes even if only a quadrupole mode exists initially.
949 citations
TL;DR: In this paper, a nonrelativistic potential theory for gravity is proposed, which is built on the basic assumptions of the modified dynamics, which were shown earlier to reproduce dynamical properties of galaxies and galaxy aggregates without having to assume the existence of hidden mass.
Abstract: We consider a nonrelativistic potential theory for gravity which differs from the Newtonian theory. The theory is built on the basic assumptions of the modified dynamics, which were shown earlier to reproduce dynamical properties of galaxies and galaxy aggregates without having to assume the existence of hidden mass. The theory involves a modification of the Poisson equation and can be derived from a Lagrangian. The total momentum, angular momentum, and (properly defined) energy of an isolated system are conserved. The center-of-mass acceleration of an arbitrary bound system in a constant external gravitational field is independent of any property of the system. In other words, all isolated objects fall in exactly the same way in a constant external gravitational field (the weak equivalence principle is satisfied). However, the internal dynamics of a system in a constant external field is different from that of the same system in the absence of the external field, in violation of the strong principle of equivalence. These two results are consistent with the phenomenological requirements of the modified dynamics. We sketch a toy relativistic theory which has a nonrelativistic limit satisfying the requirements of the modified dynamics.
887 citations
TL;DR: In this article, the evolution of linear perturbations about a Friedmann-Robertson-Walker background metric, using only the local conservation of energy momentum, has been discussed, and it has been shown that on sufficiently large scales the curvature perturbation on spatial hypersurfaces of uniform density is conserved when the non-adiabatic pressure is negligible.
Abstract: We discuss the evolution of linear perturbations about a Friedmann-Robertson-Walker background metric, using only the local conservation of energy momentum. We show that on sufficiently large scales the curvature perturbation on spatial hypersurfaces of uniform density is conserved when the non-adiabatic pressure perturbation is negligible. This is the first time that this result has been demonstrated independently of the gravitational field equations. A physical picture of long-wavelength perturbations as being composed of separate Robertson-Walker universes gives a simple understanding of the possible evolution of the curvature perturbation, in particular clarifying the conditions under which super-horizon curvature perturbations may vary.
873 citations