451 research outputs found
Nonlocal General Relativity
A brief account of the present status of the recent nonlocal generalization
of Einstein's theory of gravitation is presented. The main physical assumptions
that underlie this theory are described. We clarify the physical meaning and
significance of Weitzenb\"ock's torsion, and emphasize its intimate
relationship with the gravitational field, characterized by the Riemannian
curvature of spacetime. In this theory, nonlocality can simulate dark matter;
in fact, in the Newtonian regime, we recover the phenomenological Tohline-Kuhn
approach to modified gravity. To account for the observational data regarding
dark matter, nonlocality is associated with a characteristic length scale of
order 1 kpc. The confrontation of nonlocal gravity with observation is briefly
discussed.Comment: 23 pages; v:2 slightly expanded version. Dedicated to the memory of
M. Hossein Partovi (1941-2014
Virial Theorem in Nonlocal Newtonian Gravity
Nonlocal gravity is the recent classical nonlocal generalization of
Einstein's theory of gravitation in which the past history of the gravitational
field is taken into account. In this theory, nonlocality appears to simulate
dark matter. The virial theorem for the Newtonian regime of nonlocal gravity
theory is derived and its consequences for "isolated" astronomical systems in
virial equilibrium at the present epoch are investigated. In particular, for a
sufficiently isolated nearby galaxy in virial equilibrium, the galaxy's
baryonic diameter---namely, the diameter of the smallest sphere that completely
surrounds the baryonic system at the present time---is predicted to be larger
than the effective dark matter fraction times a universal length that is the
basic nonlocality length scale of about 3 kpc.Comment: 15 pages; v2: expanded versio
Gravitomagnetism and the Clock Effect
The main theoretical aspects of gravitomagnetism are reviewed. It is shown
that the gravitomagnetic precession of a gyroscope is intimately connected with
the special temporal structure around a rotating mass that is revealed by the
gravitomagnetic clock effect. This remarkable effect, which involves the
difference in the proper periods of a standard clock in prograde and retrograde
circular geodesic orbits around a rotating mass, is discussed in detail. The
implications of this effect for the notion of ``inertial dragging'' in the
general theory of relativity are presented. The theory of the clock effect is
developed within the PPN framework and the possibility of measuring it via
spaceborne clocks is examined.Comment: 27 pages, LaTeX, submitted to Proc. Bad Honnef Meeting on: GYROS,
CLOCKS, AND INTERFEROMETERS: TESTING GENERAL RELATIVITY IN SPACE (22 - 27
August 1999; Bad Honnef, Germany
Acceleration-Induced Nonlocality: Uniqueness of the Kernel
We consider the problem of uniqueness of the kernel in the nonlocal theory of
accelerated observers. In a recent work, we showed that the convolution kernel
is ruled out as it can lead to divergences for nonuniform accelerated motion.
Here we determine the general form of bounded continuous kernels and use
observational data regarding spin-rotation coupling to argue that the kinetic
kernel given by is the only physically acceptable
solution.Comment: LaTeX file, 2 figures, 14 page
Relativistic Effects in the Motion of the Moon
The main general relativistic effects in the motion of the Moon are briefly
reviewed. The possibility of detection of the solar gravitomagnetic
contributions to the mean motions of the lunar node and perigee is discussed.Comment: LaTeX file, no figures, 13 pages, to appear in: 'Testing relativistic
gravity in space', edited by C. Laemmerzahl, C.W.F. Everitt and F.W. Hehl
(Springer, Berlin 2000
Mach's Principle and the Origin of Inertia
The current status of Mach's principle is discussed within the context of
general relativity. The inertial properties of a particle are determined by its
mass and spin, since these characterize the irreducible unitary representations
of the inhomogeneous Lorentz group. The origin of the inertia of mass and
intrinsic spin are discussed and the inertia of intrinsic spin is studied via
the coupling of intrinsic spin with rotation. The implications of spin-rotation
coupling and the possibility of history dependence and nonlocality in
relativistic physics are briefly mentioned.Comment: 14 pages. Dedicated to Carl Brans in honor of his 80th birthday. To
appear in the Brans Festschrift; v2: typo corrected, published in: At the
Frontier of Spacetime, edited by T. Asselmeyer-Maluga (Springer, 2016),
Chapter 10, pp. 177-18
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