Near zone dynamical effects in gravity

Abstract

Dynamical effects in general relativity have been finally, relatively recently observed by LIGO [B. P. Abbott et al., Living Rev. Relativity 19, 1 (2016).]. These effects correspond to gravitational waves created by the coalescence of black holes or neutron stars billions of years ago and billions of light years away from their sources. To be able to measure these signals, great care has to be taken to minimize all sources of noise in the detector. One of the sources of noise is called Newtonian noise, the name based on the notion that close by sources would create essentially instantaneous Newtonian gravitational fields. In this article we present an analysis of the dynamical (time dependent) nature of the Newtonian noise. In that respect, it is a misnomer to call it Newtonian noise, because the Newtonian theory does not afford any dynamical notion of the gravitational field. We will, in fact, do our analysis in the context of Einsteinian general relativity. The dynamical aspects of the nature of the Newtonian noise have heretofore been disregarded as they were considered negligible. However, we demonstrate that they are indeed not far from the realm of being measurable. They could be used to validate Einsteinian general relativity or to give valuable information on the true dynamical nature of gravity. One fundamental question, for example, is a direct measurement the speed of propagation of gravitational effects and the verification that it is indeed the same as the speed of light? We propose a simple laboratory experiment that could affirm or deny this proposition. We also analyze the possibility of the detection of large geophysical events, such as earthquakes. We find that large seismic events seem to be easily observable with the present ensemble of gravitational wave detectors. The ensemble of gravitational wave detectors could easily serve as a system of early warning for otherwise catastrophic seismic events.