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In this thesis we study the dynamics of cosmological scenarios inspired by quantum gravity. Part I investigates novel features of the semi-classical regime of homogeneous and isotropic loop quantum cosmology. Dynamics in this regime becomes modified by nonperturbative quantum effects, subject to a number of ambiguities. For a flat universe the quantum effects accelerate a scalar field along its self-interaction potential during a period of super-inflation. We study how this behaviour can in principle set the initial conditions for subsequent slow-roll inflation. We also calculate a first approximation for the spectrum of perturbations produced during the super-inflationary phase. For the positively-curved case we investigate how a bounce from a contracting to an expanding phase can occur, and show that this can lead to oscillations of the universe. During the oscillations the inflaton field can roll monotonically up its potential. Once the potential energy becomes sufficiently large, however, the cycles end and inflation commences. For a constant potential the oscillations occur about a centre fixed point allowing the construction of `new emergent universe' scenarios where the universe is past-eternally an Einstein static universe, but subsequently evolves into inflation. Part II considers positively-curved braneworld models in which the dynamical equations become modified in such a way as to permit a bounce. It is conjectured that models of this type can exhibit similar behaviour to the positively-curved LQC scenario. General conditions for this behaviour are determined in braneworld settings and we investigate an explicit example - the baneworld of Shtanov and Sanhi - in detail

The detection of gravitational waves from the coalescence of two compact objects has been brought to within touching distance by the construction and operation of a global network of laser-interferometer detectors. However, the amplitude of the radiation from these events is so low that direct detection will require the combined innovations of advanced interferometry and detector characterisation, along with powerful methods of extracting weak, but modelled, signals from the background detector noise. This work focuses on enhancing the probability of such detection through improved identi�cation of noise artefacts in the instrumental data, and improved signal processing and extraction. We begin with a recap of the theory of gravitational waves as derived from Einstein's theory of gravity, and the mechanisms that allow propagation of this radiation away from a source. We also catalogue a number of promising astrophysical progenitors, with a focus on compact binary coalescences. We detail the interactions between gravitational waves and an observer, and describe the layout of the large-scale laser interferometers that have been built to enable direct detection. A description of the operation of these detectors during the last science run is given, focusing on their stability and sensitivity, isolating a number of key instrumental noise mechanisms and how they a�ected astrophysical searches over the data. Additionally, we illustrate a new method to improve the identi�cation of seismic noise bursts, allowing their removal from search data, improving search sensitivity. The LIGO and Virgo gravitational-wave detectors operated as a network during the last joint science run. A summary is given of the analysis pipeline used to search for gravitational waves signals from compact binary coalescences using a coincidence-based method, including details of the results of that analysis. Details are also given of the pipeline used to search for gravitational waves associated with short, hard gamma-ray bursts, in which a new coherent method was tuned to search over the reduced parameter space constrained by the electromagnetic counterpart. Finally, we present a new pipeline adapting the coherent method to the blind, all-sky, all-time search, allowing for a more sensitive analysis, as demonstrated by direct comparison.

La précision dans la mesure du temps est considérée par l’historiographie comme un élément qui a émergé simultanément avec la géométrisation des phénomènes naturels. Les savants du XVIIe siècle sont ainsi étudiés dans ce cadre comme des Philosophes Naturels qui considèrent comme seul argument fiable les résultats quantitatifs de mesure et de précision. Dans cette thèse nous avons étudié cette émergence, dans le cadre emblématique de la théorie gravitationnelle de Newton. Dans un premier temps nous avons défini la précision du temps comme un élément qui demande une amélioration constante par le biais des instruments. Nous avons ensuite découpé la connaissance scientifique en trois parties distinctes : la construction de la théorie, son application et la confirmation de cette dernière. Nous avons étudié la précision dans la mesure du temps et son rôle en tant qu’élément de validation dans les trois parties en mettant l’accent sur la première. Dans ce cadre d’étude nous avons démontré que la thèse couramment répandue dans l’historiographie jusqu’ici est problématique. La précision dans la mesure du temps n’a pas de relation de causalité directe avec la géométrisation de la nature. Son importance au sein des théories, au cas par cas, est évolutive et s’est pendant longtemps retrouvée cantonnée dans les aspects techniques du savoir avant de trouver en retour une place importante dans la théorie. L’étude des aspects techniques nous ont amené à l’exploration de documents liés à la détermination des longitudes en mer, et sa relation intrinsèque au développement du commerce entre continents. Dans ce cadre nous avons détaillé des aspects jusque là obscurs du « mesureur de temps » de Galilée, proposé par ce dernier comme un instrument de grande précision qui participe à la solution des longitudes. / Precision in time measurement is considered by historiography as an element that emerged simultaneously with the geometrization of natural phenomena. The scholars of the seventeenth century are therefore studied in this context as Natural Philosophers who consider as the only reliable argument the quantitative results of measurement and precision. In this thesis we have studied this emergence, in the emblematic framework of Newton's gravitational theory. At first we defined the accuracy of time as an element that requires constant improvement through the instruments. We then divided the scientific knowledge into three distinct parts: the construction of the theory, its application and the confirmation of the theory. We studied the accuracy (here as synonym of precision) in the measurement of time and its role as a validation element in all three parts with a focus on the former. In this framework of study we have shown that the thesis commonly used in historiography so far is problematic. Precision in the measurement of time has no direct causal relation with the geometrization of nature. Its importance in theories, on a case-by-case study, is evolutionary and has for a long time been confined to the technical aspects of knowledge before finding an important place in the theory. The study of technical aspects led us to explore documents related to the determination of longitudes at sea, and its intrinsic relationship to the development of trade between continents. In this context we have detailed previously unclear aspects of Galileo's "time measurer", proposed by the later as an instrument of great accuracy being part of the longitude solution.