83,571 research outputs found
A characterization of the central shell-focusing singularity in spherical gravitational collapse
We give a characterization of the central shell-focusing curvature
singularity that can form in the spherical gravitational collapse of a bounded
matter distribution obeying the dominant energy condition. This
characterization is based on the limiting behaviour of the mass function in the
neighbourhood of the singularity. Depending on the rate of growth of the mass
as a function of the area radius R, the singularity may be either covered or
naked. The singularity is naked if this growth rate is slower than R, covered
if it is faster than R, and either naked or covered if the growth rate is same
as R.Comment: 12 pages, Latex, significantly revised version, including change of
title. Revised version to appear in Classical and Quantum Gravit
The connection between `emergence of time from quantum gravity' and `dynamical collapse of the wave-function in quantum mechanics'
There are various reasons to believe that quantum theory could be an emergent
phenomenon. Trace Dynamics is an underlying classical dynamics of non-commuting
matrices, from which quantum theory and classical mechanics have been shown to
emerge, in the thermodynamic approximation. However, the time that is used to
describe evolution in quantum theory is an external classical time, and is in
turn expected to be an emergent feature - a relic of an underlying theory of
quantum gravity. In this essay we borrow ideas from Trace Dynamics to show that
classical time is a thermodynamic approximation to an operator time in quantum
gravitational physics. This prediction will be put to test by ongoing
laboratory experiments attempting to construct superposed states of macroscopic
objects.Comment: 6 pages. References updated. To appear in Int. J. Mod. Phys. D
[special issue
A note on the thermodynamics of gravitational radiation
It is shown that linearized gravitational radiation confined in a cavity can
achieve thermal equilibrium if the mean density of the radiation and the size
of the cavity satisfy certain constraints.Comment: 8 pages; discussion expanded and some issues clarified; revised
version accepted for publication in Classical and Quantum Gravit
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