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  1. Time Remains.Sean Gryb & Karim P. Y. Thébault - 2016 - British Journal for the Philosophy of Science 67 (3):663-705.
    On one popular view, the general covariance of gravity implies that change is relational in a strong sense, such that all it is for a physical degree of freedom to change is for it to vary with regard to a second physical degree of freedom. At a quantum level, this view of change as relative variation leads to a fundamentally timeless formalism for quantum gravity. Here, we will show how one may avoid this acute ‘problem of time’. Under our view, (...)
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  2. The Role of Time in Relational Quantum Theories.Sean Gryb & Karim Thébault - 2012 - Foundations of Physics 42 (9):1210-1238.
    We propose a solution to the problem of time for systems with a single global Hamiltonian constraint. Our solution stems from the observation that, for these theories, conventional gauge theory methods fail to capture the full classical dynamics of the system and must therefore be deemed inappropriate. We propose a new strategy for consistently quantizing systems with a relational notion of time that does capture the full classical dynamics of the system and allows for evolution parametrized by an equitable internal (...)
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  3.  44
    Schrodinger Evolution for the Universe: Reparametrization.Karim P. Y. Thebault & Sean Gryb - unknown
    Starting from a generalized Hamilton-Jacobi formalism, we develop a new framework for constructing observables and their evolution in theories invariant under global time reparametrizations. Our proposal relaxes the usual Dirac prescription for the observables of a totally constrained system and allows one to recover the influential partial and complete observables approach in a particular limit. Difficulties such as the non-unitary evolution of the complete observables in terms of certain partial observables are explained as a breakdown of this limit. Identification of (...)
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  4.  15
    On the Universality of Hawking Radiation.Sean Gryb, Patricia Palacios & Karim Thebault - 2019 - British Journal for the Philosophy of Science:axz025.
    A physically consistent semi-classical treatment of black holes requires universality arguments to deal with the `trans-Planckian' problem where quantum spacetime effects appear to be amplified such that they undermine the entire semi-classical modelling framework. We evaluate three families of such arguments in comparison with Wilsonian renormalization group universality arguments found in the context of condensed matter physics. Our analysis is framed by the crucial distinction between robustness and universality. Particular emphasis is placed on the quality whereby the various arguments are (...)
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  5.  31
    Symmetry and Evolution in Quantum Gravity.Sean Gryb & Karim Thébaault - 2014 - Foundations of Physics 44 (3):305-348.
    We propose an operator constraint equation for the wavefunction of the Universe that admits genuine evolution. While the corresponding classical theory is equivalent to the canonical decomposition of General Relativity, the quantum theory contains an evolution equation distinct from standard Wheeler–DeWitt cosmology. Furthermore, the local symmetry principle—and corresponding observables—of the theory have a direct interpretation in terms of a conventional gauge theory, where the gauge symmetry group is that of spatial conformal diffeomorphisms (that preserve the spatial volume of the Universe). (...)
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  6.  12
    Bouncing Unitary Cosmology I. Mini-Superspace General Solution.Sean Gryb & Karim Thebault - unknown
    We offer a new proposal for cosmic singularity resolution based upon a quantum cosmology with a unitary bounce. This proposal is illustrated via a novel quantization of a mini-superspace model in which there can be superpositions of the cosmological constant. This possibility leads to a finite, bouncing unitary cosmology. Whereas the usual Wheeler–DeWitt cosmology generically displays pathological behaviour in terms of non-finite expectation values and non-unitary dynamics, the finiteness and unitarity of our model are formally guaranteed. For classically singular models (...)
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  7.  76
    Regarding the `Hole Argument' and the `Problem of Time'.Karim P. Y. Thebault & Sean Gryb - 2016 - Philosophy of Science 83 (4):563-584.
    The canonical formalism of general relativity affords a particularly interesting characterisation of the infamous hole argument. It also provides a natural formalism in which to relate the hole argument to the problem of time in classical and quantum gravity. In this paper we examine the connection between these two much discussed problems in the foundations of spacetime theory along two interrelated lines. First, from a formal perspective, we consider the extent to which the two problems can and cannot be precisely (...)
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  8.  11
    Superpositions of the Cosmological Constant Allow for Singularity Resolution and Unitary Evolution in Quantum Cosmology.Sean Gryb & Karim P. Y. Thébault - unknown
    A novel approach to quantization is shown to allow for superpositions of the cosmological constant in isotropic and homogeneous mini-superspace models. Generic solutions featuring such superpositions display: i) a unitary evolution equation; ii) singularity resolution; iii) a cosmic bounce. Explicit cosmological solutions are constructed. These exhibit characteristic bounce features including a ‘super-inflation’ regime with universal phenomenology that can naturally be made to be insensitive to Planck-scale physics.
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  9.  6
    Bouncing Unitary Cosmology II. Mini-Superspace Phenomenology.Sean Gryb & Karim Thebault - unknown
    A companion paper provides a proposal for cosmic singularity resolution based upon general features of a bouncing unitary cosmological model in the mini-superspace approximation. This paper analyses novel phenomenology that can be identified within particular solutions of that model. First, we justify our choice of particular solutions based upon a clearly articulated and observationally motivated principle. Second, we demonstrate that the chosen solutions follow a classical mini- superspace cosmology before smoothly bouncing off the classically singular region. Third, and most significantly, (...)
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  10.  16
    On the Empirical Consequences of the AdS/CFT Duality.Radin Dardashti, Richard Dawid, Sean Gryb & Karim P. Y. Thebault - unknown
    We provide an analysis of the empirical consequences of the AdS/CFT duality with reference to the application of the duality in a fundamental theory, effective theory and instrumental context. Analysis of the first two contexts is intended to serve as a guide to the potential empirical and ontological status of gauge/gravity dualities as descriptions of actual physics at the Planck scale. The third context is directly connected to the use of AdS/CFT to describe real quark-gluon plasmas. In the latter context, (...)
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  11. On the Empirical Consequences of the AdS/CFT Duality.Radin Dardashti, Richard Dawid, Sean Gryb & Karim Thebault - 2020 - In Nick Huggett, Keizo Matsubara & Christian Wüthrich (eds.), Beyond Spacetime. Cambridge, UK: pp. 284-303.
     
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  12.  35
    Ψ-Epistemic Quantum Cosmology?Peter W. Evans, Sean Gryb & Karim P. Y. Thébault - 2016 - Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 56:1-12.
    This paper provides a prospectus for a new way of thinking about the wavefunction of the universe: a Ψ-epistemic quantum cosmology. We present a proposal that, if successfully implemented, would resolve the cosmological measurement problem and simultaneously allow us to think sensibly about probability and evolution in quantum cosmology. Our analysis draws upon recent work on the problem of time in quantum gravity and causally symmet- ric local hidden variable theories. Our conclusion weighs the strengths and weaknesses of the approach (...)
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    Bouncing Unitary Cosmology II. Mini-Superspace Phenomenology:Mini-Superspace Phenomenology.Sean Gryb & Karim P. Y. Thébault - unknown
    A companion paper provides a proposal for cosmic singularity resolution based upon general features of a bouncing unitary cosmological model in the mini-superspace approximation. This paper analyses novel phenomenology that can be identified within particular solutions of that model. First, we justify our choice of particular solutions based upon a clearly articulated and observationally-motivated principle. Second, we demonstrate that the chosen solutions follow a classical mini-superspace cosmology before smoothly bouncing off the classically singular region. Third, and most significantly, we identify (...)
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  14.  3
    New Difficulties for the Past Hypothesis.Sean Gryb - 2021 - Philosophy of Science 88 (3):511-532.
    I argue that explanations for time asymmetry in terms of a ‘Past Hypothesis’ face serious new difficulties. First I strengthen grounds for existing criticism by outlining three categories of criticism that put into question essential requirements of the proposal. Then I provide a new argument showing that any time-independent measure on the space of models of the universe must break a gauge symmetry. The Past Hypothesis then faces a new dilemma: reject a gauge symmetry and introduce a distinction without difference (...)
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