893 research outputs found
Classical Black Hole Production In Quantum Particle Collisions
The semiclassical picture of black hole production in trans-Planckian
elementary particle collisions is reviewed.Comment: 5 pages, 7 figures; talk given at the 6th Alexander Friedmann
International Seminar on Gravitation and Cosmology, Cargese, France, June
28-July 3, 2004; to appear in the proceedings (Int.J.Mod.Phys.A); v2: typos
correcte
A Relativistic Description of Gentry's New Redshift Interpretation
We obtain a new expression of the Friedmann-Robertson-Walker metric, which is
an analogue of a static chart of the de Sitter space-time. The reduced metric
contains two functions, and , which are interpreted as,
respectively, the mass function and the gravitational potential. We find that,
near the coordinate origin, the reduced metric can be approximated in a static
form and that the approximated metric function, , satisfies the
Poisson equation. Moreover, when the model parameters of the
Friedmann-Robertson-Walker metric are suitably chosen, the approximated metric
coincides with exact solutions of the Einstein equation with the perfect fluid
matter. We then solve the radial geodesics on the approximated space-time to
obtain the distance-redshift relation of geodesic sources observed by the
comoving observer at the origin. We find that the redshift is expressed in
terms of a peculiar velocity of the source and the metric function, ,
evaluated at the source position, and one may think that this is a new
interpretation of {\it Gentry's new redshift interpretation}.Comment: 11 pages. Submitted to Modern Physics Letters
Gamma-ray bursts as the birth-cries of black holes
The origin of cosmic gamma-ray bursts remains one of the most intriguing
puzzles in astronomy. We suggest that purely general relativistic effects in
the collapse of massive stars could account for these bursts. The late
formation of closed trapped surfaces can occur naturally, allowing the escape
of huge energy from curvature-generated fireballs, before these are hidden
within a black hole.Comment: 4 pages Revtex, 1 figure. This essay received an honorable mention in
the Gravity Research Foundation essay competitio
On the Nature of Singularities in Plane Symmetric Scalar Field Cosmologies
The nature of the initial singularity in spatially compact plane symmetric
scalar field cosmologies is investigated. It is shown that this singularity is
crushing and velocity dominated and that the Kretschmann scalar diverges
uniformly as it is approached. The last fact means in particular that a maximal
globally hyperbolic spacetime in this class cannot be extended towards the past
through a Cauchy horizon. A subclass of these spacetimes is identified for
which the singularity is isotropic.Comment: 7 pages, MPA-AR-94-
The role of the quantum properties of gravitational radiation in the dete ction of gravitational waves
The role that the quantum properties of a gravitational wave could play in
the detection of gravitational radiation is analyzed. It is not only
corroborated that in the current laser-interferometric detectors the resolution
of the experimental apparatus could lie very far from the corresponding quantum
threshold (thus the backreaction effect of the measuring device upon the
gravitational wave is negligible), but it is also suggested that the
consideration of the quantum properties of the wave could entail the definition
of dispersion of the measurement outputs. This dispersion would be a function
not only of the sensitivity of the measuring device, but also of the
interaction time (between measuring device and gravitational radiation) and of
the arm length of the corresponding laser- interferometer. It would have a
minimum limit, and the introduction of the current experimental parameters
insinuates that the dispersion of the existing proposals could lie very far
from this minimum, which means that they would show a very large dispersion.Comment: 19 pages, Latex (use epsfig.sty
Estimates for the volume of a Lorentzian manifold
We prove new estimates for the volume of a Lorentzian manifold and show
especially that cosmological spacetimes with crushing singularities have finite
volume.Comment: 8 pages, a pdf version of the preprint can also be retrieved from
http://www.math.uni-heidelberg.de/studinfo/gerhardt/LM-Volume.pdf v2: A
further estimate has been added covering the case when the mean curvature is
merely non-negative resp. non-positive (Theorem 1.1
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