Spelling suggestions: "subject:"relativity (physics)"" "subject:"oblativity (physics)""
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As estruturas necessárias à teoria da relatividade restrita : um estudo a partir da epistemologia genética /Penteado, Marianna Loureiro. January 2018 (has links)
Orientador: Ricardo Pereira Tassinari / Banca: Osvaldo Frota Pessoa Júnior / Banca: Marcelo Carbone Carneiro / Resumo: Esta Pesquisa se insere na área de Epistemologia Genética. O objetivo geral desta Pesquisa é discutir as estruturas necessárias ao conhecimento da Teoria da Relatividade Restrita de Albert Einstein segundo o Modelo do Sistema de Esquema de Ações e Operações sobre Símbolos e Signos (MoSEAOSS), um modelo baseado na Epistemologia Genética de Jean Piaget. Com vista a esse objetivo, são objetivos específicos desta Pesquisa: discutir os fenômenos da dilatação dos tempos e da contração dos comprimentos consequentes dos postulados da Teoria da Relatividade Restrita, assim como o Paradoxo dos Gêmeos, e, com base neles, analisar a noção de espaço-tempo que deles resultam; apresentar o MoSEAOSS, assim como os principais conceitos nele envolvidos, em especial, os conceitos de transfiguração e de transignação; aplicar o MoSEAOSS à Teoria da Relatividade Restrita e mostrar que a noção de espaço-tempo pode ser explicada por meio de operações que o sujeito realiza sobre símbolos e signos. / Abstract: This research is in the area of Genetic Epistemology. The overall goal of this research is to discuss the necessary structures for knowing Albert Einstein's Special Theory of Relativity according to the Model of the System of Schemes of Actions and Operations on Symbols and Signs (MoSEAOSS), a model based on Jean Piaget's Genetic Epistemology. The specific objectives of this research are: to discuss the phenomena of Time Dilation and Length Contraction that follow the postulates of Special Theory of Relativity, as well as the Twin Paradox, and, based on them, to analyze the notion of space-time that results from them; to introduce the MoSEAOSS, as well as the key concepts involved in it, especially, the concepts of transfiguration and transignation; to apply the MoSEAOSS to Special Theory of Relativity and to show that the notion of space-time can be explained by means of operations that the subject performs on symbols and signs. / Mestre
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Gravitoelectromagnetism and the question of stability in general relativityStark, Elizabeth January 2004 (has links)
Abstract not available
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Fundamental aspects of the expansion of the universe and cosmic horizonsDavis, Tamara Maree, Physics, Faculty of Science, UNSW January 2004 (has links)
We use standard general relativity to clarify common misconceptions about fundamental aspects of the expansion of the Universe. In the context of the new standard Lambda-CDM cosmology we resolve conflicts in the literature regarding cosmic horizons and the Hubble sphere (distance at which recession velocity equals c) and we link these concepts to observational tests. We derive the dynamics of a non-comoving galaxy and generalize previous analyses to arbitrary FRW universes. We also derive the counter-intuitive result that objects at constant proper distance have a non-zero redshift. Receding galaxies can be blueshifted and approaching galaxies can be redshifted, even in an empty universe for which one might expect special relativity to apply. Using the empty universe model we demonstrate the relationship between special relativity and Friedmann-Robertson-Walker cosmology. We test the generalized second law of thermodynamics (GSL) and its extension to incorporate cosmological event horizons. In spite of the fact that cosmological horizons do not generally have well-defined thermal properties, we find that the GSL is satisfied for a wide range of models. We explore in particular the relative entropic "eworth"e of black hole versus cosmological horizon area. An intriguing set of models show an apparent entropy decrease but we anticipate this apparent violation of the GSL will disappear when solutions are available for black holes embedded in arbitrary backgrounds. Recent evidence suggests a slow increase in the fine structure constant over cosmological time scales. This raises the question of which fundamental quantities are truly constant and which might vary. We show that black hole thermodynamics may provide a means to discriminate between alternative theories invoking varying constants, because some variations in the fundamental "econstants"e could lead to a violation of the generalized second law of thermodynamics.
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Spatially-homogeneous Vlasov-Einstein dynamicsOkabe, Takahide 05 October 2012 (has links)
The influence of matter described by the Vlasov equation, on the evolution of anisotropy in the spatially-homogeneous universes, called the Bianchi cosmologies, is studied. Due to the spatial-homogeneity, the Einstein equations for each Bianchi Type are reduced to a set of coupled ordinary differential equations, which has Hamiltonian form with the metric components being the canonical coordinates. In the vacuum Bianchi cosmologies, it is known that a curvature potential, which comes from the symmetries of the three-dimensional Lie groups, determines the basic properties of the evolution of anisotropy. In this work, matter potentials are constructed for Vlasov matter. They are obtained by first introducing a new matter action principle for the Vlasov equation, in terms of a conjugate pair of functions, and then enforcing the symmetry to obtain a reduction. This yields an expression for the matter potential in terms of the phase space density, which is further reduced by assuming cold streaming matter. Some vacuum Bianchi cosmologies and Type I with Vlasov matter are compared. It is shown that the Vlasov-matter potential for cold streaming matter results in qualitatively distinct dynamics from the well-known vacuum Bianchi cosmologies. / text
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Constrained evolution in numerical relativityAnderson, Matthew William 28 August 2008 (has links)
Not available / text
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Computational and astrophysical studies of black hole spacetimesBonning, Erin Wells 28 August 2008 (has links)
Not available / text
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Radiating solutions with heat flow in general relativity.Govender, Megandren. January 1994 (has links)
In this thesis we model spherically symmetric radiating stars dissipating energy in
the form of a radial heat flux. We assume that the spacetime for the interior matter
distribution is shear-free. The junction conditions necessary for the matching of the
exterior Vaidya solution to an interior radiating line element are obtained. In particular
we show that the pressure at the boundary of the star is nonvanishing when the
star is radiating (Santos 1985). The junction conditions, with a nonvanishing cosmological
constant, were obtained. This generalises the results of Santos (1985) and we
believe that this is an original result. The Kramer (1992) model is reviewed in detail
and extended. The evolution of this model depends on a function of time which has
to satisfy a nonlinear second order differential equation. We solve this differential
equation in general and thereby completely describe the temporal behaviour of the
Kramer model. Graphical representations of the thermodynamical and gravitational
variables are generated with the aid of the software package MATHEMATICA Version
2.0 (Wolfram 1991). We also analyse two other techniques to generate exact
solutions to the Einstein field equations for modelling radiating stars. In the first
case the particle trajectories are assumed to be geodesics. We indicate how the model
of Kolassis et al (1988) may be extended by providing an ansatz to solve a second
order differential equation. In the second case we review the models of de Oliveira
et al (1985, 1986, 1988) where the gravitational potentials are separable functions of
the spatial and temporal coordinates. / Thesis (M.Sc.)-University of Natal, 1994.
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Spherically symmetric cosmological solutions.Govender, Jagathesan. January 1996 (has links)
This thesis examines the role of shear in inhomogeneous spherically symmetric spacetimes
in the field of general relativity. The Einstein field equations are derived for
a perfect fluid source in comoving coordinates. By assuming a barotropic equation
of state, two classes of nonaccelerating solutions are obtained for the Einstein field
equations. The first class has equation of state p = ⅓µ and the second class, with
equation of state p = µ, generalises the models of Van den Bergh and Wils (1985).
For a particular choice of a metric potential a new class of solutions is found which
is expressible in terms of elliptic functions of the first and third kind in general. A
class of nonexpanding cosmological models is briefly studied. The method of Lie
symmetries of differential equations generates a self-similar variable which reduces
the field and conservation equations to a system of ordinary differential equations.
The behaviour of the gravitational field in this case is governed by a Riccati equation
which is solved in general. Another class of solutions is obtained by making an ad
hoc choice for one of the gravitational potentials. It is demonstrated that for a stiff
fluid a particular case of the generalised Emden-Fowler equation arises. / Thesis (Ph.D.)-University of Natal, Durban, 1996.
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Conformally invariant relativistic solutions.Maharaj, M. S. January 1993 (has links)
The study of exact solutions to the Einstein and Einstein-Maxwell field equations,
by imposing a symmetry requirement on the manifold, has been the subject of much
recent research. In this thesis we consider specifically conformal symmetries in static
and nonstatic spherically symmetric spacetimes. We find conformally invariant solutions,
for spherically symmetric vectors, to the Einstein-Maxwell field equations
for static spacetimes. These solutions generalise results found previously and have
the advantage of being regular in the interior of the sphere. The general solution to
the conformal Killing vector equation for static spherically symmetric spacetimes is
found. This solution is subject to integrability conditions that place restrictions on
the metric functions. From the general solution we regain the special cases of Killing
vectors, homothetic vectors and spherically symmetric vectors with a static conformal
factor. Inheriting conformal vectors in static spacetimes are also identified. We
find a new class of accelerating, expanding and shearing cosmological solutions in
nonstatic spherically symmetric spacetimes. These solutions satisfy an equation of
state which is a generalisation of the stiff equation of state. We also show that this
solution admits a conformal Killing vector which is explicitly obtained. / Thesis (Ph.D.)-University of Natal, Durban, 1993.
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Conformal motions in Bianchi I spacetime.Lortan, Darren Brendan. January 1992 (has links)
In this thesis we study the physical properties of the manifold in general relativity that admits a conformal motion. The results obtained are general as the metric tensor field is not specified. We obtain the Lie derivative along a conformal Killing vector of the kinematical and dynamical quantities for the general energy-momentum tensor of neutral matter. Equations obtained previously are regained as special cases from our results. We also find the Lie derivative of the energy-momentum tensor for the electromagnetic field. In particular we comprehensively study conformal symmetries in the Bianchi I spacetime. The conformal Killing vector equation is integrated to obtain the general conformal Killing vector and the conformal factor subject to
integrability conditions. These conditions place restrictions on the metric functions. A particular solution is exhibited which demonstrates that these conditions have a nonempty solution set. The solution obtained is a generalisation of the results of Moodley (1991) who considered locally rotationally symmetric spacetimes. The Killing vectors are regained as special cases of the conformal solution. There do not exist any proper special conformal Killing vectors in the Bianchi I spacetime. The homothetic vector is found for a nonvanishing constant conformal factor. We establish that the vacuum Kasner solution is the only Bianchi I spacetime that admits a homothetic vector. Furthermore we isolate a class of vectors from the solution which causes the Bianchi I model to degenerate into a spacetime of higher symmetry. / Thesis (M.Sc.)-University of KwaZulu-Natal, 1992.
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