21,850 research outputs found
Imagining Action in/Against the Anthropocene: Narrative Impasse and the Necessity of Alternatives to Effect Resistance
The Anthropocene has emerged as the dominant conception of the contemporary moment, centering the human individual as both responsible for and bearing the responsibility to counteract its numerous interrelated socioeconomic, political, and environmental issues including the staggering loss of biodiversity across the globe and the reality of anthropogenic climate change. This constitutes a significant psychological impasse that disempowers and disenfranchises humans living in this epoch, discouraging any substantive individual effort. Drawing on the posthuman feminist philosophy of theorists such as Rosi Braidotti and Stacy Alaimo together with a reflection of the power of science fiction as a literature of cognitive estrangement highlighting social issues, this paper reads “The Boston Hearth Project” by T.X. Watson as a short story demonstrative of an ethos of community and hope that resists the negative affects and oppressive social structures of the Anthropocene. I argue in the course of this paper that theorists and activists alike must turn to alternative narratives, such as those modelled in the emergent science fiction genre of solarpunk, in order to reject essentializing and individualizing forces and think multiply in order to realize meaningful resistance in a time of increasing fragmentation in society and destruction of the more-than-human world
A new class of obstructions to the smoothness of null infinity
Expansions of the gravitational field arising from the development of
asymptotically Euclidean, time symmetric, conformally flat initial data are
calculated in a neighbourhood of spatial and null infinities up to order 6. To
this ends a certain representation of spatial infinity as a cylinder is used.
This set up is based on the properties of conformal geodesics. It is found that
these expansions suggest that null infinity has to be non-smooth unless the
Newman-Penrose constants of the spacetime, and some other higher order
quantities of the spacetime vanish. As a consequence of these results it is
conjectured that similar conditions occur if one were to take the expansions to
even higher orders. Furthermore, the smoothness conditions obtained suggest
that if a time symmetric initial data which is conformally flat in a
neighbourhood of spatial infinity yields a smooth null infinity, then the
initial data must in fact be Schwarzschildean around spatial infinity.Comment: 24 pages, 4 figure
Asymptotic simplicity and static data
The present article considers time symmetric initial data sets for the vacuum
Einstein field equations which in a neighbourhood of infinity have the same
massless part as that of some static initial data set. It is shown that the
solutions to the regular finite initial value problem at spatial infinity for
this class of initial data sets extend smoothly through the critical sets where
null infinity touches spatial infinity if and only if the initial data sets
coincide with static data in a neighbourhood of infinity. This result
highlights the special role played by static data among the class of initial
data sets for the Einstein field equations whose development gives rise to a
spacetime with a smooth conformal compactification at null infinity.Comment: 25 page
Perturbations of the asymptotic region of the Schwarzschild-de Sitter spacetime
The conformal structure of the Schwarzschild-de Sitter spacetime is analysed
using the extended conformal Einstein field equations. To this end, initial
data for an asymptotic initial value problem for the Schwarzschild-de Sitter
spacetime is obtained. This initial data allows to understand the singular
behaviour of the conformal structure at the asymptotic points where the
horizons of the Schwarzschild-de Sitter spacetime meet the conformal boundary.
Using the insights gained from the analysis of the Schwarzschild-de Sitter
spacetime in a conformal Gaussian gauge, we consider nonlinear perturbations
close to the Schwarzschild- de Sitter spacetime in the asymptotic region. We
show that small enough perturbations of asymptotic initial data for the
Schwarzschild de-Sitter spacetime give rise to a solution to the Einstein field
equations which exists to the future and has an asymptotic structure similar to
that of the Schwarzschild-de Sitter spacetime.Comment: Accepted version in Ann. Henri Poincar\'e. Title change: "Conformal
properties of the Schwarzschild-de Sitter spacetime" to "Perturbations of the
asymptotic region of the Schwarzschild-de Sitter spacetime". Sections
reorganised. 64 pages, 10 figure
Asymptotic properties of the development of conformally flat data near spatial infinity
Certain aspects of the behaviour of the gravitational field near null and
spatial infinity for the developments of asymptotically Euclidean, conformally
flat initial data sets are analysed. Ideas and results from two different
approaches are combined: on the one hand the null infinity formalism related to
the asymptotic characteristic initial value problem and on the other the
regular Cauchy initial value problem at spatial infinity which uses Friedrich's
representation of spatial infinity as a cylinder. The decay of the Weyl tensor
for the developments of the class of initial data under consideration is
analysed under some existence and regularity assumptions for the asymptotic
expansions obtained using the cylinder at spatial infinity. Conditions on the
initial data to obtain developments satisfying the Peeling Behaviour are
identified. Further, the decay of the asymptotic shear on null infinity is also
examined as one approaches spatial infinity. This decay is related to the
possibility of selecting the Poincar\'e group out of the BMS group in a
canonical fashion. It is found that for the class of initial data under
consideration, if the development peels, then the asymptotic shear goes to zero
at spatial infinity. Expansions of the Bondi mass are also examined. Finally,
the Newman-Penrose constants of the spacetime are written in terms of initial
data quantities and it is shown that the constants defined at future null
infinity are equal to those at past null infinity.Comment: 24 pages, 1 figur
On the existence and convergence of polyhomogeneous expansions of zero-rest-mass fields
The convergence of polyhomogeneous expansions of zero-rest-mass fields in
asymptotically flat spacetimes is discussed. An existence proof for the
asymptotic characteristic initial value problem for a zero-rest-mass field with
polyhomogeneous initial data is given. It is shown how this non-regular problem
can be properly recast as a set of regular initial value problems for some
auxiliary fields. The standard techniques of symmetric hyperbolic systems can
be applied to these new auxiliary problems, thus yielding a positive answer to
the question of existence in the original problem.Comment: 10 pages, 1 eps figur
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