64,859 research outputs found

    Stellar structure and compact objects before 1940: Towards relativistic astrophysics

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    Since the mid-1920s, different strands of research used stars as "physics laboratories" for investigating the nature of matter under extreme densities and pressures, impossible to realize on Earth. To trace this process this paper is following the evolution of the concept of a dense core in stars, which was important both for an understanding of stellar evolution and as a testing ground for the fast-evolving field of nuclear physics. In spite of the divide between physicists and astrophysicists, some key actors working in the cross-fertilized soil of overlapping but different scientific cultures formulated models and tentative theories that gradually evolved into more realistic and structured astrophysical objects. These investigations culminated in the first contact with general relativity in 1939, when J. Robert Oppenheimer and his students George Volkoff and Hartland Snyder systematically applied the theory to the dense core of a collapsing neutron star. This pioneering application of Einstein's theory to an astrophysical compact object can be regarded as a milestone in the path eventually leading to the emergence of relativistic astrophysics in the early 1960s.Comment: 83 pages, 4 figures, submitted to the European Physical Journal

    On the relation between modality and tense

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    ABSTRACT We critically review two extant paradigms for understanding the systematic interaction between modality and tense, as well as their respective modifications designed to do justice to the contingency of time’s structure and composition. We show that on either type of theory, as well as their respective modifications, some principles prove logically valid whose truth might sensibly be questioned on metaphysical grounds. These considerations lead us to devise a more general logical framework that allows accommodation of those metaphysical views that its predecessors rule out by fiat

    Whewell\'s Wager: The Continuing Dialogue of Metaphysics and Physics in Science

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    In his library at Trinity College, Cambridge University, around the year I860, William Whewell (1794-1866) engages in conversation with a company of thinkers on the province of metaphysics and physics, to form a comprehensive scientific belief. In attendance with him are Lord Francis Bacon (1561-1626), Sir Robert Boyle (1627-1691 ), Sir Isaac Newton (1642-1727) , John Henry Cardinal Newman (1801-1890), Professor Alfred North Whitehead (1861-1947), and Pope John Paul II (b. 1920). Whewell proposes a wager: Is there a possible remedy to be found for the schism between the metaphysical and the physical elements of science

    Abstract Body, Abstract Machine: Alan Turing's Drama of Difference

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    In order to prove that mathematics cannot be exhausted by a finite set of procedures, Alan Turing conceives, in 1936, of an abstract machine 1. The machine makes its debut in “On Computable Numbers with an application to the Entscheidungsproblem,” his first major mathematical paper 2. A close reading of this machine’s dynamic will show that Turing’s thought in the field of mathematics is a consciously embodied thought that contemplates its own incompleteness. By examining Turing’s machine through the lens of incompleteness, this project will reveal how, through his extension into abstraction, Turing engages in a paradoxically intensive movement that reveals his body as inextricably enfolded in thought. To understand this radical act of contemplation, Turing must be situated within a history of thinkers working against totality, because in thinking his own incompleteness, he refutes the idea that systems are defined by completeness, or that the unfolding of something is circumscribed by that something as goal. This constellation of thinkers includes Kurt Gödel, before Turing, with his Incompleteness Theorem 3; it also includes Gilles Deleuze, with his explanation of how meaning gets made in The Logic of Sense ,4 and Michel Foucault, with his formulation of meaning’s dissolution in “The Thought of the Outside.”5 Brian Massumi then ushers this tradition into the present by defining the limit of a human being as immanent to that being in Parables for the Virtual.6 Massumi grounds his theory in Deleuzeian and Foucauldian concepts, themselves built from Turing’s legacy of lived thought, which in turn is grounded in Gödel’s theorem. Explaining these writers’ relation to Turing’s work on incompleteness will reveal the way in which systems of meaning are always torn between their own constitution and dissolution; this state of being torn will clarify, in turn, the movement of Turing’s mathematical body

    Frontiers in complex dynamics

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    Rational maps on the Riemann sphere occupy a distinguished niche in the general theory of smooth dynamical systems. First, rational maps are complex-analytic, so a broad spectrum of techniques can contribute to their study (quasiconformal mappings, potential theory, algebraic geometry, etc.). The rational maps of a given degree form a finite-dimensional manifold, so exploration of this {\em parameter space} is especially tractable. Finally, some of the conjectures once proposed for {\em smooth} dynamical systems (and now known to be false) seem to have a definite chance of holding in the arena of rational maps. In this article we survey a small constellation of such conjectures centering around the density of {\em hyperbolic} rational maps --- those which are dynamically the best behaved. We discuss some of the evidence and logic underlying these conjectures, and sketch recent progress towards their resolution.Comment: 18 pages. Abstract added in migration

    The Impact on Public Trust of Image Manipulation in Science

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    Aim/PurposeIn this paper, we address the theoretical challenges today’s scientific community faces to precisely draw linesbetween true and false pictures. In particular, we focus onproblems related to the hiddenwonders ofscience and the shiny im-ages produced for scientific papers or to appeal towider audiences. BackgroundAs rumors (hoaxes) and false news (fake news)explode acrosssociety and the current network, severalinitiatives using current technologyhave been launched to study this phenomena and limit the social impact. Over the last two decades, inappropriate scientific behavior has raisedmore questions about whether some scientific images are valid.MethodologyThis work is not about analyzing whethertoday’s imagesare objective.Instead,weadvocate for a general approach thatmakes it easier to truly believe in all kinds of knowledge, scientific or otherwise (Goldman, 1967; Goldman, & Ol-son, 2009). This need to believe is closely related to social order (Shapin, 1994). ContributionWe conclude that we must ultimately move away from older ideas about truth and objectivity in research to broadly approach howscience and knowledge are represented and move forward with this theoretical approach when communi-catingscience tothe public.FindingsContemporary visual culture suggests that our world is expressed through im-ages, which areall around us. Therefore,we need to promote thereliability of scientific pictures, which visually represent knowledge, to add meaning in a world of complex high-tech science (Allamel-Raffin, 2011; Greenberg, 2004; Rosenberger, 2009). Since the time of Galileo, and today more than ever, scien-tific activity should be understood as knowledgeproduced toreveal, and there-fore inform us of, (Wise, 2006) all that remains unexplained in our world , as well as everything beyond our senses
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