36,849 research outputs found
'We are all poor here’: economic difference, social divisiveness, and targeting cash transfers in Sub-Saharan Africa
Growth of covariant perturbations in the contracting phase of a bouncing universe
In this paper we examine the validity of the linear perturbation theory near
a bounce in the covariant analysis. Some linearity parameters are defined to
set up conditions for a linear theory. Linear evolution of density perturbation
and gravitational waves have been computed previously. We have calculated the
vector and scalar induced parts of the shear tensor. For radiationlike and
dustlike single fluid dominated collapsing Friedmann-Lemaitre-Robertson-Walker
background it is shown that the linearity conditions are not satisfied near a
bounce.Comment: 9 pages, final versio
Inhomogeneity effects in Cosmology
This article looks at how inhomogeneous spacetime models may be significant
for cosmology. First it looks at how the averaging process may affect large
scale dynamics, with backreaction effects leading to effective contributions to
the averaged energy-momentum tensor. Secondly it considers how local
inhomogeneities may affect cosmological observations in cosmology, possibly
significantly affecting the concordance model parameters. Thirdly it presents
the possibility that the universe is spatially inhomogeneous on Hubble scales,
with a violation of the Copernican principle leading to an apparent
acceleration of the universe. This could perhaps even remove the need for the
postulate of dark energy.Comment: 29 pages. For special issue of CQG on inhomogeneous cosmologie
On the paradox of Hawking radiation in a maximally extended Schwarzschild solution
This paper considers the effect of Hawking radiation on an eternal black hole
- that is. a maximally extended Schwarzschild solution. Symmetry considerations
that hold independent of the details of the emission mechanism show there is an
inconsistency in the claim that such a blackhole evaporates away in a finite
time. In essence: because the external domain is static, there is an infinite
time available for the process to take place, so whenever the evaporation
process is claimed to come to completion, it should have happened earlier. The
problem is identified to lie in the claim that the locus of emission of Hawking
radiation lies just outside the globally defined event horizon. Rather, the
emission domain must be mainly located inside the event horizon, so most of the
Hawking radiation ends up at this singularity rather than at infinity and the
black hole never evaporates away. This result supports a previous claim
[arXiv:1310.4771] that astrophysical black holes do not evaporate.Comment: 26 pages, 7 figures, 2 tables. arXiv admin note: text overlap with
arXiv:1310.477
Cosmology and Local Physics
This article is dedicated to the memory of Dennis Sciama. It revisits a
series of issues to which he devoted much time and effort, regarding the
relationship between local physics and the large scale structure of the
universe - in particular, Olber's paradox, Mach's principle, and the various
arrows of time. Thus the focus is various ways in which local physics is
influenced by the universe itself.Comment: 20 pages LaTe
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