A number of philosophical questions, all connected to modern research in quantum gravity, are discussed in this dissertation. The goal of research in quantum gravity is to find a quantum theory for gravitation; the other fundamental forces are already understood in terms of quantum physics. Quantum gravity is studied within a number of different research programmes. The most popular are string theory and loop quantum gravity; besides these a number of other approaches are pursued. Due to the lack of empirical support, it is relevant to assess the scientific status of this research. This is done from four different points of view, namely the ones held by: logical positivists, Popper, Kuhn and Lakatos. It is then argued that research in quantum gravity may be considered scientific, conditional on scientists being open with the tentative and speculative nature of their pursuits. Given the lack of empirical progress, in all approaches to quantum gravity, a pluralistic strategy is advised. In string theory there are different theoretical formulations, or dualities, which are physically equivalent. This is relevant for the problem of underdetermination of theories by data, and the debate on scientific realism. Different views on the dualities are possible. It is argued that a more empiricist view on the semantics of theories, than what has been popular lately, ought to be adopted. This is of importance for our understanding of what the theories tell us about space and time. In physics and philosophy, the idea that there are worlds or universes other than our own, has appeared in different contexts. It is discussed how we should understand these different suggestions; how they are similar and how they are different. A discussion on, how and when theoretical multiverse scenarios can be empirically testable, is also given. The reliability of thought experiments in physics in general and in quantum gravity in particular is evaluated. Thought experiments can be important for heuristic purposes, but in the case of quantum gravity, conclusions based on thoght experiments are not very reliable.

This thesis investigates the interplay between explanatory issues in special relativity and the theory's metaphysical foundations. Special attention is given to the 'dynamical approach' to relativity, promoted primarily by Harvey Brown and collaborators, according to which the symmetries of dynamical laws are explanatory of relativistic effects, inertial motion, and even the Minkowskian geometrical structure of a specially relativistic world. The thesis begins with a review of Einstein's 1905 introduction to special relativity, after which brief historical introductions are given for the standard 'geometrical' approach to relativity and the unorthodox 'dynamical' approach. After a critical review of recent literature on the topic, the dynamical approach is shown to be in need of a metaphysical package that would undergird the explanatory claims mentioned above. It is argued that the dynamical approach is best understood as a form of relationalism - in particular, as a relativistic form of 'regularity relationalism', promoted recently by Nick Huggett. According to this view, some portion of a world's geometrical structure actually supervenes upon the symmetries of the best-system dynamical laws for a material ontology endowed with a primitive sub-metrical structure. To explore the plausibility of this construal of the dynamical approach, a case study is carried out on solutions to the Klein-Gordon equation. Examples are found for which the field values, when purged of all spatiotemporal structure but their induced topology, are still arguably best-systematized by the Klein-Gordon equation itself. This bolsters the plausibility of the claim that some system of field values, endowed with mere sub-metrical structure, might have as its best-systems dynamical laws a (set of) Lorentz-covariant equation(s), on which Minkowski geometrical structure would supervene. The upshot is that the dynamical approach to special relativity can be defended as what might be called an ontologically and ideologically relationalist approach to Minkowski spacetime structure. The chapters refer regularly to three appendices, which include a brief introduction to topological and differentiable spaces.

[pt] Esta investigação tem por objetivo apresentar um modelo de cooperação entre filosofia e ciência experimental, por meio de um domínio comum, a matemática, especialmente a álgebra. Essa coordenação entre dois domínios situados em níveis distintos de conhecimento da realidade natural chama-se filosofia da natureza, e havia sido proposta por Aristóteles nos oito livros da Física. Com o advento da ciência experimental moderna entre os séculos XVI e XVII, tal tipo de investigação passou a ter um caráter secundário, porquanto se entendeu que as teorias, especialmente as de base matemática, e o método experimental em conjunto seriam suficientes para dar conta da estrutura da realidade. No entanto, faz-se necessário -- e esta é nossa proposta --, em decorrência das questões de limite suscitadas pela própria ciência experimental, retomar uma investigação complementar à científica ou epistêmica, e coordenada com esta, de modo a prover um conhecimento integral, totalizante, da realidade natural. Portanto, analisa-se o alcance da ciência experimental quanto à compreensão científica da natureza da matéria, expondo certas limitações deste tipo de enfoque, tendo por base a epistemologia proposta pelo filósofo Jacques Maritain. Em seguida, analisa-se o estatuto metafísico ou ontológico da matéria, com base em vários textos de Tomás de Aquino, e propõe-se um modelo algébrico para a representação de elementos daquela ontologia. Por fim, apresentam-se algumas conseqüências que se podem extrair desse modelo, com vistas à compreensão de aspectos da realidade natural como espaço-tempo e movimento, não-localidade quântica, e uma proposta de visão totalizante da realidade física,denominada holomovimento, sugerida pelo físico David Bohm. / [en] The main purpose of this enquiry is to provide a cooperative framework for philosophy and experimental science. This should be accomplished by means of a common domain, namely mathematics, specifically through algebra. Such a coordination between two different levels of knowledge of the natural world is named philosophy of nature, and had been proposed by Aristotle in his eight book Physics. As an outcome of the rise of modern science between 16th and 17th centuries, this kind of enquiry has been left aside as a secondary enterprise. For it has been a common understanding that modern scientific theories together with experimental methods would suffice to account for the structure of reality.However, I shall propose that it is necessary -- as a consequence of edge research on experimental sciences -- to resume a complementary enquiry to the scientific (epistemic) research, in such a coordinated way with this latter as to provide a whole knowledge of the natural world. Thus, I shall analyze the concept of matter as it is understood by experimental science, and based upon Jacques Maritain´s proposed epistemology I shall present some of the shortcomings of scientific approach to matter. Shortly afterwards, I shall analyze the metaphysical (ontological) status of matter based upon several writings from Thomas Aquinas, and I shall propose an algebraic model to represent some of the ontological elements that build up matter from a metaphysical point of view. Lastly, I shall present some of the consequences that can be obtained from that model in order to gain a metaphysical understanding of physical aspects such as space-time and movement, quantum non-locality, and also a whole perspective of physical reality as proposed by David Bohm which he called holomovement.

There have been recent explosions of interest in two fields: Madhyamaka-Pyrrhonism parallels and Pyrrhonism itself, which seems to have been misunderstood and therefore neglected by the West for the same reasons and in the same ways that Madhyamaka traditionally has often been by the West and the East. Among these recent studies are several demonstrating that grounding in Madhyamaka, for example, reveals and illuminates the import and insights of Pyrrhonean arguments. Furthermore it has been suggested that of all European schools of philosophy Pyrrhonism is the one closest to Buddhism, and especially to Madhyamaka. Indeed Pyrrho is recorded to have studied with philosophers in Taxila, one of the first places where Madhyamaka later flourished, and the place where the founder of Madhyamaka, Nāgārjuna, may have received hitherto concealed texts which became the foundation for his school. In this dissertation I explore just how similar these two philosophical projects were. I systematically treat all the arguments in the Pyrrhonist redactor Sextus Empiricus’ Outlines of Pyrrhonism and Against Dogmatists and compare them to the most similar arguments available in the Madhyamaka treatises and related texts. On this basis, I ask whether the Pyrrhonists and the Buddhists would satisfy each other’s self-identifying criteria, or what characteristics would disqualify either or both in the other’s eyes. I also ask what questions arise from the linguistic and historical evidence for interactions between the Pyrrhonist school and the Madhyamaka school, and how sure we can be of the answers. Did Pyrrho learn Buddhism in Taxila? Was Nāgārjuna a Pyrrhonist? Finally I bring the insights of the living commentarial tradition of Madhyamaka to bear on current scholarly controversies in the field of Sextan Pyrrhonism, and apply the subtleties of interpretation of the latter which have developed in recent scholarship to Madhyamaka and its various difficulties of interpretation, to scrutinize each school under the illumination of the other. With this hopefully illuminated view, I address for example whether Sextus was consistent, whether living Pyrrhonism implies apraxia, whether Pyrrhonism is philosophy at all, and whether Madhyamaka is actually nihilism.

Ce travail fait l’analyse du concept de « principe de coordination » tel qu’il se développe au sein de la théorie coordinative de la connaissance, et plus particulièrement au sein du mouvement empiriste-logique, à partir de la deuxième décennie du XXème siècle. Ce concept est primordial lorsqu’il s’agit de comprendre la manière dont la définition des concepts de grandeur en physique se construit comme la mise en rapport, la coordination, des variables mathématiques de la théorie avec les opérations de mesure dans le laboratoire. L’enjeu est de montrer qu’un des concepts centraux de l’empirisme au XXème siècle est utilisé initialement, par Schlick et Reichenbach, pour analyser la théorie de la relativité, mais qu’il devient rapidement l’outil d’un programme plus spécifique, entrepris par Carnap et Hempel, de reconstruction logique des théories physiques. Pourtant ce concept, pris au sein de l’épistémologie coordinative, permet un empirisme qui laisse une place au développement historique des concepts de grandeur. Analysé et compris correctement il peut permettre de poser les fondements d’un empirisme historique, au sein duquel les concepts théoriques ne seraient plus reconstruits seulement à partir des mesures empiriques, mais aussi à partir des concepts hérités de théories historiquement antérieures. / This work analyzes the concept of "principle of coordination" as it develops within the coordinative theory of knowledge, and more particularly within the empiricist-logical movement, from the second decade of the twentieth century. This concept is essential to understand the way in which the definition of the concepts of magnitude in physics is constructed as the linking, the coordination, of the mathematical variables of the theory with the measurement operations in the laboratory. The challenge is to show that one of the central concepts of empiricism in the twentieth century is used initially, by Schlick and Reichenbach, to analyze the theory of relativity, but that it quickly becomes the tool of a more specific program, undertaken by Carnap and Hempel, of logical reconstruction of physical theories. Yet this concept, along with other concepts from coordinative epistemology, allows an empiricism that leaves room for the historical development of the concepts of magnitude. Analyzed and understood correctly, it can lay the foundations of a historical empiricism, in which theoretical concepts would no longer be reconstructed only from empirical measurements, but also from concepts inherited from historically antecedent theories.

Submitted by Andrea Hayashi (deachan@gmail.com) on 2016-06-20T15:04:35Z No. of bitstreams: 1 dissertacao-luiz-ben-hassanal-machado-da-silva.pdf: 1764576 bytes, checksum: 0ab2e29a4b1972b424391d78ad6d9687 (MD5) / Approved for entry into archive by Andrea Hayashi (deachan@gmail.com) on 2016-06-20T15:05:54Z (GMT) No. of bitstreams: 1 dissertacao-luiz-ben-hassanal-machado-da-silva.pdf: 1764576 bytes, checksum: 0ab2e29a4b1972b424391d78ad6d9687 (MD5) / Made available in DSpace on 2016-06-20T15:05:54Z (GMT). No. of bitstreams: 1 dissertacao-luiz-ben-hassanal-machado-da-silva.pdf: 1764576 bytes, checksum: 0ab2e29a4b1972b424391d78ad6d9687 (MD5) Previous issue date: 2015-05-15 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Nessa investigação nos concentraremos no período de consolidação da teoria quântica, sobretudo naquilo que toca o livro A Lógica da Pesquisa Científica, de 1934. O centro da investigação é à crítica de Popper ao pensamento indutivista e subjetivista de Heisenberg, que por meio de considerações da filosofia da linguagem e com o apoio de defensores da filosofia positivista, construiu com outros partidários da chamada Interpretação de Copenhague a interpretação hegemônica da teoria quântica. O dedutivismo realista de Popper , apresentado no livro Lógica da Pesquisa Científica, visa combater essa visão, através de uma defesa da objetividade e do realismo que escapou dos limites da Epistemologia e ganhou ares éticos. Popper defendeu a Interpretação Estatística, que é um ramo da teoria corpuscular. Demonstraremos como que a interpretação acerca do alcance da Epistemologia opõe esses pensadores. Para Heisenberg a objetividade devia ser deixada de lado, a partir da constatação empírica do Princípio de Incerteza. O método científico deve, segundo o físico alemão, limitar os conceitos da linguagem clássica e aplica-los nas descrições dos fenômenos quânticos segundo as limitações operacionais dos conceitos. Para Popper, a metodologia dispensa questões linguísticas e apreende o método científico como sendo baseado na testabilidade, o que impõe que a análise epistemológica seja feita somente após a teoria ter sido conjecturada. Investigaremos a partir do pensamento de Popper e veremos como sua defesa do falseacionismo impõe uma interpretação da teoria quântica diferente daquela preconizada por Heisenberg. / In this investigation we will focus on the period of consolidation of the quantum theory, specially, on what concerns the book Logic of Scientific Discovery, of 1934. The center of this investigation is the Popper‟s critics to the inductivism and subjectivism of Heisenberg thought that, through concepts of the philosophy of language and the support of positivist philosophy advocates, built with other supporters of Copenhagen Interpretation, the hegemonic interpretation of quantum theory. The realistic deductivism of Popper, submitted in the Logic of Scientific Discovery, aim to tackle this position, through a defense of objectivity and realism that pushed the boundaries of epistemology and acquired ethical air. Popper supported the statistical interpretation of quantum theory, a branch of corpuscular interpretation. We will show how the interpretation of the epistemological range opposes these thinkers. To Heisenberg the objectivity must be set apart from the empirical realization of the Principle of Uncertainty. The scientific method, according to the German physicist, must limit the concepts of classical language and apply them in the quantum phenomena descriptions according to the operational limitations of concepts. According to Popper, the methodology exempts linguistic questions and perceives the scientific method as grounded on testability, which imposes that the epistemological analysis has to be made only after the theory has been conjectured. We will investigate from the thought of Popper and we will see how his defense of falseacionism imposes an interpretation of the quantum theory different from those preconized by Heisenberg.

I defend three general claims concerning inter-theoretic reduction in physics. First, the popular notion that a superseded theory in physics is generally a simple limit of the theory that supersedes it paints an oversimplified picture of reductive relations in physics. Second, where reduction specifically between two dynamical systems models of a single system is concerned, reduction requires the existence of a particular sort of function from the state space of the low-level (purportedly more accurate and encompassing) model to that of the high-level (purportedly less accurate and encompassing) model that approximately commutes, in a specific sense, with the rules of dynamical evolution prescribed by the models. The third point addresses a tension between, on the one hand, the frequent need to take into account system-specific details in providing a full derivation of the high-level theory’s success in a particular context, and, on the other hand, a desire to understand the general mechanisms and results that under- write reduction between two theories across a wide and disparate range of different systems; I suggest a reconciliation based on the use of partial proofs of reduction, designed to reveal these general mechanisms of reduction at work across a range of systems, while leaving certain gaps to be filled in on the basis of system-specific details. After discussing these points of general methodology, I go on to demonstrate their application to a number of particular inter-theory reductions in physics involving quantum theory. I consider three reductions: first, connecting classical mechanics and non-relativistic quantum mechanics; second,connecting classical electrodynamics and quantum electrodynamics; and third, connecting non-relativistic quantum mechanics and quantum electrodynamics. I approach these reductions from a realist perspective, and for this reason consider two realist interpretations of quantum theory - the Everett and Bohm theories - as potential bases for these reductions. Nevertheless, many of the technical results concerning these reductions pertain also more generally to the bare, uninterpreted formalism of quantum theory. Throughout my analysis, I make the application of the general methodological claims of the thesis explicit, so as to provide concrete illustration of their validity.

Si nos théories physiques peuvent décrire les traits les plus généraux de la réalité, on sait aussi que pour le faire, elles utilisent le langage des mathématiques. On peut alors légitimement se demander si notre capacité à décrire, sinon la nature intime des objets et phénomènes physiques, du moins les relations et structures qu’ils instancient, ne vient pas de cette application des mathématiques. Dans cette thèse, nous soutenons que les mathématiques sont si efficacement applicables en physique tout simplement parce que la réalité décrite par les physiciens est de nature quantitative. Pour cela, nous proposons d’abord une ontologie des quantités, puis des lois de la nature, qui s’inscrit dans les débats contemporains sur la nature des propriétés (théorie des universaux, théorie des tropes, ou nominalisme), et des lois (régularités, ou relations entre universaux). Ensuite, nous examinons deux sortes d’application des mathématiques : la mathématisation des phénomènes par la mesure, puis la formulation mathématique des équations reliant des grandeurs physiques. Nous montrons alors que les propriétés et les lois doivent être comme notre ontologie les décrit, pour que les mathématiques soient légitimement, et si efficacement, applicables. L’intérêt de ce travail est d’articuler des discussions purement ontologiques (et très anciennes, comme la querelle des universaux) avec des exigences épistémologiques rigoureuses qui émanent de la physique actuelle. Cette articulation est conçue de manière transcendantale, car la nature quantitative de la réalité (des propriétés et des lois) y est défendue comme condition d’applicabilité des mathématiques en physique. / Assuming that our best physical theories succeed in describing the most general features of reality, one can only be struck by the effectiveness of mathematics in physics, and wonder whether our ability to describe, if not the very nature of physical entities, at least their relations and the fundamental structures they enter, does not result from applying mathematics. In this dissertation, we claim that mathematical theories are so effectively applicable in physics merely because physical reality is of quantitative nature. We begin by displaying and supporting an ontology of quantities and laws of nature, in the context of current philosophical debates on the nature of properties (universals, classes of tropes, or even nominalistic resemblance classes) and of laws (as mere regularities or as relations among universals). Then we consider two main ways mathematics are applied: first, the way measurement mathematizes physical phenomena, second, the way mathematical concepts are used to formulate equations linking physical quantities. Our reasoning has eventually a transcendental flavor: properties and laws of nature must be as described by the ontology we first support with purely a priori arguments, if mathematical theories are to be legitimately and so effectively applied in measurements and equations. What could make this work valuable is its attempt to link purely ontological (and often very ancient) discussions with rigorous epistemological requirements of modern and contemporary physics. The quantitative nature of being (properties and laws) is thus supported on a transcendental basis: as a necessary condition for mathematics to be legitimately applicable in physics.

Il n’est pas évident si et dans quelle mesure la connaissance non empirique peut donner de l’information sur des systèmes physiques réels. Hume croyait que toute connaissance à propos du monde qui nous entoure ne doit sa certitude à rien d’autre que l’expérience répétée de la conjonction des causes et des effets observables. Or, il y a quelques raisons de croire que le rôle de la raison en physique dépasse celui qui lui est attribué par Hume. Le principe de la moindre action est un bon candidat, pour quelques raisons : il a été découvert à partir d’un argument métaphysique, il rivalise avec les lois de Newton au titre de fondement de la mécanique classique, et il a fini par motiver le développement de nombreux formalismes qui lui sont propres jusqu’au sein des théories les plus récentes de la physique. Nous analyserons les idées ayant mené à sa découverte par Pierre-Louis de Maupertuis. / It is unclear whether and to what extent non-empirical knowledge can provide information about real physical systems. Hume believed that all knowledge about the world around us owes its certainty to nothing other than the repeated experience of the conjunction of observable causes and effects. However, there are some reasons to believe that the role of reason in physics goes beyond that attributed to it by Hume. The principle of least action is a good candidate for a number of reasons : it was discovered from a metaphysical argument, it rivals Newton’s laws as the foundation of classical mechanics, and it eventually motivated the development of several formalisms in a wide variety of the most recent theories of physics. We will analyze the ideas that led to its discovery by Pierre-Louis de Maupertuis.

In this thesis I discuss the nature of ‘measurement’ in quantum theory. ‘Measurement’ is associated with several different processes: the gradual imprinting of information about one system onto another, which is well understood; the collapse of the wavefunction, which is ill-defined and troublesome; and finally, the means by which inferences about unknown experimental parameters are made. I present a theoretical extension to an experimental proposal from Leggett and Garg, who suggested that the quantum-or-classical reality of a macroscopic system may be probed with successive measurements arrayed in time. The extension allows for a finite level of imperfection in the protocol, and makes use of Leggett’s ‘null result’ measurement scheme. I present the results of an experiment conducted in Oxford that, up to certain loopholes, defies a non-quantum interpretation of the dynamics of phosphorous nuclei embedded in silicon. I also present the theory of statistical parameter estimation, and discover that a recent trend to employ time symmetric ‘postselected’ measurements offers no true advantage over standard methods. The technique, known as weak-value amplification, combines a weak transfer of quantum information from system to meter with conditional data rejection, to surprising effect. The Fisher information is a powerful tool for evaluating the performance of any parameter estimation model, and it reveals the technique to be worse than ordinary, preselected only measurements. That this is true despite the presence of noise (including magnetic field fluctuations causing deco- herence, poor resolution detection, and random displacements), casts serious doubt on the utility of the method.