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  1. Bryan W. Roberts (2014). A General Perspective on Time Observables. Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 47:50-54.
    I propose a general geometric framework in which to discuss the existence of time observables. This framework allows one to describe a local sense in which time observables always exist, and a global sense in which they can sometimes exist subject to a restriction on the vector fields that they generate. Pauli[U+05F3]s prohibition on quantum time observables is derived as a corollary to this result. I will then discuss how time observables can be regained in modest extensions of quantum theory (...)
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  2. Bryan W. Roberts, Comment on Ashtekar: Generalization of Wigner's Principle.
    Ashtekar (2013) has illustrated that two of the available roads to testing for time asymmetry can be generalized beyond the structure of quantum theory, to much more general formulations of mechanics. The purpose of this note is to show that a third road to T-violation, which I have called "Wigner's Principle," can be generalized in this way as well.
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  3. Gordon Belot, Mark J. Schervish, Teddy Seidenfeld, Joseph B. Kadane, Miles MacLeod, Nancy J. Nersessian, Hylarie Kochiras, Bryan W. Roberts, Elay Shech & Richard Healey (2013). 1. Bayesian Orgulity Bayesian Orgulity (Pp. 483-503). Philosophy of Science 80 (4).
     
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  4. Bryan W. Roberts (2013). The Simple Failure of Curie's Principle. Philosophy of Science 80 (4):579-592.
    I point out a simple sense in which the standard formulation of Curie’s principle is false when the symmetry transformation it describes is time reversal.
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  5. John D. Norton & Bryan W. Roberts (2012). Galileo's Refutation of the Speed-Distance Law of Fall Rehabilitated. Centaurus 54 (2):148-164.
    Galileo's refutation of the speed-distance law of fall in his Two New Sciences is routinely dismissed as a moment of confused argumentation. We urge that Galileo's argument correctly identified why the speed-distance law is untenable, failing only in its very last step. Using an ingenious combination of scaling and self-similarity arguments, Galileo found correctly that bodies, falling from rest according to this law, fall all distances in equal times. What he failed to recognize in the last step is that this (...)
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  6. Bryan W. Roberts (2012). Kramers Degeneracy Without Eigenvectors. Physical Review A 86 (3):034103.
    Wigner gave a well-known proof of Kramers degeneracy, for time reversal invariant systems containing an odd number of half-integer spin particles. But Wigner's proof relies on the assumption that the Hamiltonian has an eigenvector, and thus does not apply to many quantum systems of physical interest. This note illustrates an algebraic way to talk about Kramers degeneracy that does not appeal to eigenvectors, and provides a derivation of Kramers degeneracy in this more general context.
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  7. Bryan W. Roberts, Time, Symmetry and Structure: A Study in the Foundations of Quantum Theory.
    This dissertation is about the sense in which the laws of quantum theory distinguish between the past and the future. I begin with an account of what it means for quantum theory to make such a distinction, by providing a novel derivation of the meaning of "time reversal." I then show that if Galilei invariant quantum theory does distinguish a preferred direction in time, then this has consequences for the ontology of the theory. In particular, it requires matter to admit (...)
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  8. Bryan W. Roberts, When We Do (and Do Not) Have a Classical Arrow of Time.
    I point out that some common folk wisdom about time reversal invariance in classical mechanics is strictly incorrect, by showing some explicit examples in which classical time reversal invariance fails, even among conservative systems. I then show that there is nevertheless a broad class of familiar classical systems that are time reversal invariant.
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  9. Bryan W. Roberts (2011). Group Structural Realism. British Journal for the Philosophy of Science 62 (1):47-69.
    We present a precise form of structural realism, called group structural realism , which identifies ‘structure’ in quantum theory with symmetry groups. However, working out the details of this view actually illuminates a major problem for structural realism; namely, a structure can itself have structure. This article argues that, once a precise characterization of structure is given, the ‘metaphysical hierarchy’ on which group structural realism rests is overly extravagant and ultimately unmotivated.
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  10. Bryan W. Roberts (2011). How Galileo Dropped the Ball and Fermat Picked It Up. Synthese 180 (3):337-356.
    This paper introduces a little-known episode in the history of physics, in which a mathematical proof by Pierre Fermat vindicated Galileo’s characterization of freefall. The first part of the paper reviews the historical context leading up to Fermat’s proof. The second part illustrates how a physical and a mathematical insight enabled Fermat’s result, and that a simple modification would satisfy any of Fermat’s critics. The result is an illustration of how a purely theoretical argument can settle an apparently empirical debate.
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