General Relativity: The Most Beautiful of Theories: Applications and Trends After 100 Years by Rovelli Carlo

Author:Rovelli, Carlo [Rovelli, Carlo]
Language: eng
Format: epub
Publisher: De Gruyter
Published: 2015-01-26T16:00:00+00:00

Ignazio Ciufolini

General Relativity and dragging of inertial frames

Abstract: Dragging of inertial frames, or frame-dragging, is an intriguing and fascinating phenomenon predicted by Einstein’s theory of General Relativity with relevant astrophysical effects in the vicinities of rotating black holes. The first part of this paper is devoted to the theory of this phenomenon and the second part is devoted to its experimental confirmations. We first discuss the relation of frame-dragging to the riddle of the origin of inertia and inertial forces (Section 1.1). Frame-dragging can be described, in a weak gravitational field with slow motions, by a useful formal analogy with electrodynamics and is for this reason often called gravitomagnetism (Sections 1.2 and 1.3). To shed light on the riddle of the origin of inertia, it is interesting to study the behaviour of test particles, gyroscopes, and light and clocks inside a rotating sphere (Section 1.4). The phenomena caused by a rotating body or by a current of mass on the flow of time and clocks are especially fascinating (Section 1.5). Time-delay in the propagation of photons inside a rotating sphere might, in principle, be observed by gravitational lensing and by the rotation of an external cluster of galaxies (Sections 1.6 and 1.6.1). In principle, if measured, that effect might give information about the nature of dark matter and dark energy. In a strong gravitational field, frame-dragging may be defined with the use of curvature invariants (Section 1.7 ). Then, after briefly describing the past experimental triumph of General Relativity (Section 2.1), we describe the need to further test General Relativity, alternative theories and unified theories, including gravitational interaction, and the enigma of dark energy (Sections 2.2 and 2.3). We finally present the limits set on string theories, of Chern–Simons type, by using the current measurements of frame-dragging with the LAGEOS and LAGEOS 2 satellites, and the future improvement of these limits with the LARES satellite (Section 2.4). In the second part we review the previous experimental tests of frame-dragging which were obtained using the LAGEOS satellites and with the dedicated Gravity Probe B space mission which reported an accuracy of about 10% and 19% in their measurements in 2004–2011 and 2011, respectively (Section 3). To confirm the robustness of the results obtained with the LAGEOS satellites, we report similar results for the measurement of frame-dragging which were obtained independently by three different groups: the Universities of Salento, Maryland and Rome “Sapienza”; the University of Texas at Austin; and GFZ Potsdam. The three groups used in their analyses the three independent orbital programs GEODYN, UTOPIA and EPOS-OC, respectively. Finally, we present the LARES space experiment, which together with LAGEOS, LAGEOS 2, and the determinations of the Earth’s gravitational field by GRACE will improve the accuracy

Ignazio Ciufolini: Dip. Ingegneria dell’Innovazione, Università del Salento, Lecce, and Centro Fermi, Rome, Italy

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