According to current cosmological theory, the rate of expansion of the universe depends on the average energy densities of matter, radiation, and a possible vacuum energy described by a cosmological constant, &Lambda;, in the Einstein equation.<p>Observations of galaxies and radiation, along with an assumption that we hold no special place in the universe, imply an isotropic and homogeneous energy distribution, for which the universal rate of expansion for most of the history of the universe may be constructed to depend only on present values of the dimensionless matter and vacuum energy density parameters, &Omega;_M and &Omega;_&Lambda;, respectively, and the present rate of expansion of the universe, H₀. Over the past decade, much progress has been made in determining the values of the three density parameters using a variety of independent methods. In particular, observations of type Ia supernovae in the late 1990s provided the first evidence that &Lambda; &ne; 0 and that universal expansion is accelerating.<p>This study has determined values for &Omega;_M and &Omega;_&Lambda; using the brightest quasars in the Sloan Digital Sky Survey Data Release 5, which are located at a range of distances - equivalently, a range of lookback times - that have not been accessible through any other observations. After fitting the apparent magnitudes of the brightest quasars at various redshifts to the distance modulus equation with a luminosity evolution term, values for the density parameters were determined to be &Omega;_M = 0.07 and &Omega;_&Lambda; = 1.13.

Thesis (Ph. D.)--University of Chicago, Department of Astronomy and Astrophysics, June 2001. / Includes bibliographical references. Also available on the Internet.

The General theory of Relativity (GR) brought gravity into accord with the principles of locality and relativity. Since its discovery it has been preeminent, recognized as the most accurate description of gravity on the many scales where it has been tested. During this period, seemingly radical predictions like the existence of black holes and the expansion of the Universe have been verified and testify to the great leap of insight that GR represented in our understanding of space and time. However not all precision observations of astrophysical systems have yielded easily to interpretation within GR, and with the discovery of cosmic acceleration, there is genuine concern that General Relativity may be incomplete when describing the Universe on the largest sizes imaginable. In this uncertainty, many theoretical models have been proposed. In this thesis we shall first outline the motivation behind a certain subset of these models and the known issues that arise in interpreting these models as alternative theories of gravity. Then focus on one variety of theory the f(R) modifications to gravity. Demonstrating that many of the known instabilities have a common origin and that they are avoided when treating these theories via perturbative constraints. In the second part of this work we examine the astrophysical impact of modifications to gravity, first in the case of high mass neutron stars, then subsequently on corrections to the line profile of neutral hydrogen from violations of the equivalence principle. Finally we explore the phenomenology of modifications to gravity that produce late-Universe acceleration. In particular, what solutions are allowed and what range of accelerations are predicted as a result. Furthermore we explore how a correction to gravity at large scales would impact the growth and evolution of cosmological perturbations.

Baryon acoustic oscillations (BAOs) are used to obtain precision measurements of cosmological parameters from large-scale surveys. While robust against most systematics, there are certain theoretical uncertainties that can affect BAO and galaxy clustering measurements. In this thesis I use data from the Sloan Digital Sky Survey (SDSS) to measure cosmological parameters and use N-body and smoothed-particle hydrodynamic (SPH) simulations to measure the effect of theoretical uncertainties by using halo occupation distributions (HODs). I investigate the effect of galaxy bias on BAO measurements by creating mock galaxy catalogs from large N -body simulations at z = 1. I find that there is no additional shift in the acoustic scale (0.10% ± 0.10%) for the less biased HODs (b < 3) and a mild shift (0.79% ± 0.31%) for the highly biased HODs (b > 3). I present the methodology and implementation of the simple one-step reconstruction technique introduced by Eisenstein et al. (2007) to biased tracers in N-body simulation. Reconstruction reduces the errorbars on the acoustic scale measurement by a factor of 1.5 - 2, and removes any additional shift due to galaxy bias for all HODs (0.07% ± 0.15%). Padmanabhan et al. (2012) and Xu et al. (2012) use this reconstruction technique in the SDSS DR7 data to measure Dᵥ(z = 0.35)(rᶠⁱᵈs/rs) = 1356 ± 25 Mpc. Here I use this measurement in combination with measurements from the cosmic microwave background and the supernovae legacy survey to measure various cosmological parameters. I find the data consistent with the ΛCDM Universe with a flat geometry. In particular, I measure H₀ = 69.8 ± 1.2 km/s/Mpc, w = 0.97 ± 0.17, Ωk = -0.004 ± 0.005 in the ΛCDM, wCDM, and oCDM models respectively. Next, I measure the effect of large-scale (5 Mpc) halo environment density on the HOD by using an SPH simulation at z = 0, 0.35, 0.5, 0.75, 1.0. I do not find any significant dependence of the HOD on the halo environment density for different galaxy mass thresholds, red and blue galaxies, and at different redshifts. I use the MultiDark N-body simualtion to measure the possible effect of environment density on the galaxy correlation function ℰ(r). I find that environment density enhances ℰ(r) by ∽ 3% at scales of 1 – 20h⁻¹Mpc at z = 0 and up to ∽ 12% at 0.3h⁻¹Mpc and ∽ 8% at 1 - 4h⁻¹Mpc for z = 1.

The following dissertation is a philosophical exploration of the cosmology of the Zhuangzi, arguing it is meontological due to the prominence afforded the Chinese word wu 無, rendered as both nothingness and nonbeing. It puts forth the argument that the Zhuangzi’s cosmology creates a relationship whereby nonbeing and being are intertwined under the purview of Dao 道. As a result, the text’s axiology is unique in that it states cosmological freedom is attainable via uniting with primal nothingness. Chapter one seeks to disprove the notion that nonbeing cannot be anything but a transcendental other by arguing that Dao is a negatively creative source that simultaneously gives birth to nonbeing and being, making it impossible for nonbeing to be nihilistic or seen as an absolute void. Chapter two delves into the manifestation of things and how the sage, as an epitome of the naturalness of Dao, follows the becoming and returning of things to the One, darkening himself in nothingness in order to cultivate his life. Chapter three poses the question of whether or not the ontological movement of things is temporal and how temporality can even be possible considering the meontological nature of the universe. The next two chapters focus on the arts of useful uselessness and forgetting, the two principal means by which the sage achieves harmony with the oneness of things. Chapter six concludes by arguing that freedom attained by perfecting the arts of uselessness and forgetfulness is not rooted in ethical virtue but is the pinnacle of one’s cosmological relationship with Dao and is embodied in the act of carefree wandering. Zhuangzi’s cosmology is thus rooted in the life force of nothingness and doing away with ontic distinctions so as to return to natural equanimity and stillness of spirit.

The following dissertation is a philosophical exploration of the cosmology of the Zhuangzi, arguing it is meontological due to the prominence afforded the Chinese word wu 無, rendered as both nothingness and nonbeing. It puts forth the argument that the Zhuangzi’s cosmology creates a relationship whereby nonbeing and being are intertwined under the purview of Dao 道. As a result, the text’s axiology is unique in that it states cosmological freedom is attainable via uniting with primal nothingness. Chapter one seeks to disprove the notion that nonbeing cannot be anything but a transcendental other by arguing that Dao is a negatively creative source that simultaneously gives birth to nonbeing and being, making it impossible for nonbeing to be nihilistic or seen as an absolute void. Chapter two delves into the manifestation of things and how the sage, as an epitome of the naturalness of Dao, follows the becoming and returning of things to the One, darkening himself in nothingness in order to cultivate his life. Chapter three poses the question of whether or not the ontological movement of things is temporal and how temporality can even be possible considering the meontological nature of the universe. The next two chapters focus on the arts of useful uselessness and forgetting, the two principal means by which the sage achieves harmony with the oneness of things. Chapter six concludes by arguing that freedom attained by perfecting the arts of uselessness and forgetfulness is not rooted in ethical virtue but is the pinnacle of one’s cosmological relationship with Dao and is embodied in the act of carefree wandering. Zhuangzi’s cosmology is thus rooted in the life force of nothingness and doing away with ontic distinctions so as to return to natural equanimity and stillness of spirit.

The consistency of fundamental constants is assumed in the Standard Model. However, new physics theories allow them to be dynamical. Different tests can be made at various epochs of the universe. In particular, current bounds at the time of emission of the Cosmic Microwave Background (CMB) permit variations up to 1% of their present values. A change of this order can produce an accumulation of tritium which would later decay and modify the ionization history of the Universe by up to O(0.1%). This Tritium Decay Scenario (TDS) can modify the CMB to an observable level and thus provides a new probe of Varying Fundamental Constants (VFC). We analyze the WMAP 7-year and SPT data with respect to the TDS and find no evidence for VFC. The data disfavors a portion of the parameter space at 95% Confidence Level (CL). We forecast the sensitivity of Planck to the TDS and find that a larger range of parameters can be excluded at 3σ CL. / Graduate

Bibliography: leaves 152-156 / ix, 156 leaves : ill ; 31 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, 1986

Master of Science / General Relativity (GR) is founded on the revolutionary idea that space and time are merely parts of a greater, unified whole: spacetime. Furthermore, the force we know as gravity results from the bending and stretching of the geometry of spacetime by its energetic contents. GR is notorious for its mathematical complexity and subtlety, meaning that an intuitive understanding of a spacetime is difficult. One of the best approaches to studying the properties of a given spacetime is to consider its geodesic structure—that is, to consider the motion of unaccelerated, “free-falling” particles. This report presents the results of such a study into two important spacetimes — the Kerr solution for a rotating black hole, and the Robertson-Walker solution for a homogeneous universe.

Thesis (Ph. D.)--University of New South Wales, 2003. / Also available online.