published_or_final_version / Physics / Doctoral / Doctor of Philosophy

Syftet med den här uppsatsen är att utföra de la Fuente et al:s (2014) experiment med priming av temporalt fokus hos arbisktalande individer med svenska som andraspråk. De frågor som undersöks är i vilken utsträckning de la Fuente et al:s temporalfokushypotes är generaliserbar till fler språkgrupper än spansktalande, vilka primingeffekterna blir hos individerna, samt vilka faktorer som inverkar på det temporala fokuset utöver primingen. Metoden är att återupprepa det experiment de la Fuente et al. gjort med spansktalande, genom att återutföra det på en grupp arabisktalande individer med svenska som andraspråk. Resultatet av föreliggande studies upprepning av de la Fuentes experiment på arabisktalande, visar att primingeffekterna uteblir, men att faktorer som vistelsetid och ålder inverkar påvisbart på tidsrepresentationen. Utbildningsbakgrund visar tendenser till att inverka på tidsrepresentationen. Ett temporalt fokus påverkbart av yttre stimuli går inte att påvisa i den här studien, varför delar av temporalfokushypotesen inte är generaliserbar till alla språkgrupper.

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We employ a stochastic approach that models spacetime fluctuations close to the Planck scale by means of a classical, randomly fluctuating metric (random gravity framework).  We enrich the classical scheme for metric perturbations over a curved background by also including matter fields and metric conformal fluctuations.  We show in general that a conformally modulated metric induces dephasing as a result of an effective nonlinear Newtonian potential obtained in the appropriate non-relativistic limit of a minimally coupled Klein-Gordon field.  The special case of vacuum fluctuations is considered and a quantitative estimate of the expected effect deduced. Secondly, we address the question of how conformal fluctuations could physically arise.  By applying the random gravity framework we first show that standard GR seems to forbid spontaneous conformal metric modulations.  Finally we argue that a different result follows within scalar-tensor theories of gravity such as e.g. Brans-Dicke theory. In this case a conformal modulation of the metric arises naturally as a result of the fluctuations in the Brans-Dicke field and quantum dephasing of a test particle is expected to occur.  For large negative values of the coupling parameter the conformal fluctuations may also contribute to alleviate the well known problem of the large zero point energy due to quantum matter fields.

ΛCDM cosmology is described in terms of general relativity and the Robertson-Walker metric. The evolution of the observable universe, currently dominated by dark energy (Λ) and cold dark matter (CDM), is presented in terms of its thermal history. CDM is extended to include an inflation epoch that accelerates the early expansion rate to near exponential levels. It is shown that inflation solves several problems in CDM and produces perturbations in the metric that lead to the observed anisotropies in the Cosmic Microwave Background and the formation of large scale cosmological structures. Various theories of inflation are explored. Predictions of inflation theories are compared to observations published by the Planck Collaboration. The paper concludes with an examination of “𝜶-attractor” theories of inflation based on a modified form of gravity.

Standard models of cosmology use inflation as a mechanism to resolve the isotropy and homogeneity problem of the universe as well as the flatness problem. However, due to various well known problems with the inflationary paradigm, there has been an ongoing search for alternatives. Perhaps the most famous among these are the cyclic universe scenarios which incorporate bounces. As these scenarios have a contracting phase in the evolution of the universe, anisotropies and inhomogeneities would be expected to blow up on approach to the bounce. Thus, it is reasonable to ask whether the problems of homogeneity and isotropy can still be resolved in these scenarios. In this thesis, I will focus on the problem of the resolution of the isotropy problem. I begin with a brief review of anisotropic, spatially homogeneous geometries of cosmological interest. Next, I review the existing literature on bouncing cosmologies, and discuss the mechanism of bounce studied in previously proposed models, as well as their theoretical and observational advantages and disadvantages. I then discuss the process of isotropisation in the contracting phase of each bounce. In this phase of the evolution, the mechanism of ekpyrosis is used in most cosmological scenarios which incorporate a contracting phase to mitigate the problem of anisotropies blowing up on approaching the bounce. I start by studying anisotropic universes and I then examine the effect of the addition of ultra-stiff anisotropic pressures on the ekpyrotic phase. I then consider evolving such anisotropic universes through several cycles with increasing expansion maxima at each successive bounce. This eventually leads to flatness in the isotropic case. My aim is to see if the resolution of the flatness problem also leads to a simultaneous resolution of the isotropy problem. In the next chapter, I consider the effect of non comoving velocities on the shape of this anisotropic bouncing universe. In the final section of my thesis, I consider anisotropic cosmological models within the context of canonical quantum cosmology and investigate the quantum behaviour of anisotropies.

Chan Kin Hang. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (leaves 66-67). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Weighted Sobolev Spaces --- p.3 / Chapter 2.1 --- Weighted Sobolev Spaces --- p.3 / Chapter 2.2 --- Some Basic Properties of Weighted Sobolev Spaces --- p.4 / Chapter 2.3 --- Δon Rn in Weighted Sobolev Spaces --- p.14 / Chapter 2.4 --- Δg on Asymptotically Flat Manifolds --- p.20 / Chapter 3 --- Uniqueness of Structure at Infinity --- p.32 / Chapter 3.1 --- More on Δg --- p.32 / Chapter 3.2 --- Uniqueness of Structure of Infinity --- p.34 / Chapter 4 --- Uniqueness of Mass --- p.40 / Chapter 4.1 --- Definition of Mass --- p.40 / Chapter 4.2 --- Uniqueness of Mass --- p.41 / Chapter 5 --- Schwarzschild Metric and Vacuum Einstein Equation --- p.50 / Chapter 5.1 --- Static Spacetime and Spherically Symmetric Spacetime --- p.50 / Chapter 5.2 --- Schwarzschild Vacuum Solution --- p.57 / Chapter 5.2.1 --- Equation Solving --- p.57 / Chapter 5.3 --- Birkhoff's Theorem --- p.59 / Chapter 5.4 --- Asymptotically Flat Properties of Space with Schwarzschild Metric --- p.61 / Chapter 5.5 --- Mass of The Space Induced by Schwarzschild Metric --- p.64 / Bibliography --- p.66

This thesis considers various extensions to the fluid/gravity correspondence as well as problems fundamental to the study of fluid dynamics. The fluid/gravity correspondence is a map between the solutions of the Navier-Stokes equations of fluid dynamics and the solutions of the Einstein equations in one higher spatial dimension. This map arose within the context of string theory and holography and is a specific realisation of a much wider class of dualities known as the Anti de Sitter/Conformal Field Theory (AdS/CFT) correspondence. The first chapter is an introduction; the second chapter reviews the fluid/gravity correspondence. The next two chapters extend existing work on the fluid/gravity map. Our first result concerns the fluid/gravity map for forced fluid dynamics in arbitrary spacetime dimensions. Forced fluid flows are of particular interest as they are known to demonstrate turbulent behaviour. For the case of a fluid with a dilaton-dependent forcing term, we present explicit expressions for the dual bulk metric, the fluid dynamical stress tensor and Lagrangian to second order in boundary spacetime derivatives. Our second result concerns fluid flows with multiple anomalous currents in the presence of external electromagnetic fields. It has recently been shown using thermodynamic arguments that the entropy current for such anomalous fluids contains additional first order terms proportional to the vorticity and magnetic field. Using the fluid/gravity map, we replicate this result using gravitational methods. The final two chapters consider questions related to the equations of fluid dynamics themselves; these chapters do not involve the fluid/gravity correspondence. The first of these chapters is a review of the various constraints that must be satisfied by the transport coefficients. In the final chapter, we derive the constraints obtained by requiring that the equilibrium fluid configurations are linearly stable to small perturbations. The inequalities that we obtain here are slightly weaker than those found by demanding that the divergence of the entropy current is non-negative.

Apresentamos neste trabalho uma generalização da teoria de perturbações cosmológicas para o caso de universos homogêneos e anisotrópicos, caracterizados por um espaço-tempo do tipo Bianchi I. Como aplicação da teoria, investigamos as conseqüências de uma fase inflacionária e anisotrópica do universo dos pontos de vista clássico e quântico. Após uma discussão da evolução do espaço-tempo de fundo nós quantizamos os modos perturbativos para, em seguida, construir o espectro de potências das perturbações de curvatura e de ondas gravitacionais do fim da inflação. Nossos resultados mostram que as principais características de uma fase anisotrópica primordial do universo são: (1) dependência direcional dos espectros de potências, (2) acoplamento entre as perturbações de curvatura e as ondas gravitacionais e (3) espectros distintos para as diferentes polarizações das ondas gravitacionais em grandes escalas cosmológicas. Todos esses efeitos são importantes apenas em grandes escalas cosmológicas e, localmente, recuperamos a teoria isotrópica de perturbações cosmológicas. Nossos resultados dependem de uma escala característica que pode, embora não seja estritamente necessário, ser ajustada a alguma escala observável. / In this work we generalize the standard theory of cosmological perturbations to the case of homogeneous and anisotropic universes described by a Bianchi I spacetime metric. As an application of this theory we investigate the predictions of an inflationary anisotropic phase, both at the classical and quantum level. After discussing the evolution of the background spacetime, we solve and quantize the perturbation equations in order to predict the power spectra of the curvature perturbations and gravity waves at the end of inflation. Our results show that the main features of an early anisotropic phase are: (1) a dependence of the spectra on the direction of the modes, (2) a coupling between curvature perturbations and gravity waves, and (3) the fact that the two gravity waves polarisations do not share the same spectrum on large scales. All these effects are significant only on large scales and die out on small scales where isotropy is recovered. Finally, our results depend on a characteristic scale that can, but a priori does not have to, be tuned to some observable scale.

There is a debate in the philosophy of time over the status of non-present entities. Do these things exist, and if so, what sorts of things are they? Recently, the debate has split into two groups, presentists and eternalists. Presentists hold that no past or future things exist now. Socrates does not now exist, though he did in the past; my future daughter does not now exist, though she may in the future. Ontologically, the present is distinct, serving to demarcate all that currently has existence. As far as the eternalist is concerned, all entities - whether past, present, or future - are equally real. If it was, is, or will be, it can be found in the eternalist picture of time. As such, there is no distinct present at which some entities exist while others do not; rather, everything enjoys the same ontological status. I will be concerned to offer an assessment of the presentist view. Common objections against presentism will be examined, amplified, and answered where appropriate. I will not examine the arguments in favor of the presentist view. Rather, I wish to describe why it is that the eternalist feels compelled to deny presentism. Ultimately, my goal will be to show that although presentism survives some of the current objections raised against it, it does not survive them all. Presentism is an interesting, but ultimately unsatisfactory view. There is a modified form of presentism (call it presentism*) that can meet the objections raised against the original position, and after noting some of the objections raised against presentism, I will sketch the outlines of presentism* in some detail. I intend to show that presentism* is able to retain what is most valuable about presentism, while also withstanding certain objections that the latter view could not.