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  1. What Are Observables in Hamiltonian Einstein–Maxwell Theory?James Pitts - 2019 - Foundations of Physics 49 (8):786-796.
    Is change missing in Hamiltonian Einstein–Maxwell theory? Given the most common definition of observables, observables are constants of the motion and nonlocal. Unfortunately this definition also implies that the observables for massive electromagnetism with gauge freedom are inequivalent to those of massive electromagnetism without gauge freedom. The alternative Pons–Salisbury–Sundermeyer definition of observables, aiming for Hamiltonian–Lagrangian equivalence, uses the gauge generator G, a tuned sum of first-class constraints, rather than each first-class constraint separately, and implies equivalent observables for equivalent massive electromagnetisms. (...)
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  • Progress and Gravity: Overcoming Divisions Between General Relativity and Particle Physics and Between Physics and HPS.J. Brian Pitts - 2017 - In Khalil Chamcham, Joseph Silk, John D. Barrow & Simon Saunders (eds.), The Philosophy of Cosmology. Cambridge University Press. pp. 263-282.
    Reflective equilibrium between physics and philosophy, and between GR and particle physics, is fruitful and rational. I consider the virtues of simplicity, conservatism, and conceptual coherence, along with perturbative expansions. There are too many theories to consider. Simplicity supplies initial guidance, after which evidence increasingly dominates. One should start with scalar gravity; evidence required spin 2. Good beliefs are scarce, so don't change without reason. But does conservatism prevent conceptual innovation? No: considering all serious possibilities could lead to Einstein's equations. (...)
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  • Defining a Crisis: The Roles of Principles in the Search for a Theory of Quantum Gravity.Karen Crowther - forthcoming - Synthese:1-28.
    In times of crisis, when current theories are revealed as inadequate to task, and new physics is thought to be required---physics turns to re-evaluate its principles, and to seek new ones. This paper explores the various types, and roles of principles that feature in the problem of quantum gravity as a current crisis in physics. I illustrate the diversity of the principles being appealed to, and show that principles serve in a variety of roles in all stages of the crisis, (...)
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  • Symplectic Reduction and the Problem of Time in Nonrelativistic Mechanics.Karim P. Y. Thebault - 2012 - British Journal for the Philosophy of Science 63 (4):789-824.
    Symplectic reduction is a formal process through which degeneracy within the mathematical representations of physical systems displaying gauge symmetry can be controlled via the construction of a reduced phase space. Typically such reduced spaces provide us with a formalism for representing both instantaneous states and evolution uniquely and for this reason can be justifiably afforded the status of fun- damental dynamical arena - the otiose structure having been eliminated from the original phase space. Essential to the application of symplectic reduction (...)
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  • Equivalent Theories and Changing Hamiltonian Observables in General Relativity.J. Brian Pitts - 2018 - Foundations of Physics 48 (5):579-590.
    Change and local spatial variation are missing in Hamiltonian general relativity according to the most common definition of observables as having 0 Poisson bracket with all first-class constraints. But other definitions of observables have been proposed. In pursuit of Hamiltonian–Lagrangian equivalence, Pons, Salisbury and Sundermeyer use the Anderson–Bergmann–Castellani gauge generator G, a tuned sum of first-class constraints. Kuchař waived the 0 Poisson bracket condition for the Hamiltonian constraint to achieve changing observables. A systematic combination of the two reforms might use (...)
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  • 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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  • Gauge Invariant Accounts of the Higgs Mechanism.Ward Struyve - 2011 - Studies in History and Philosophy of Modern Physics 42 (4):226-236.
    The Higgs mechanism gives mass to Yang-Mills gauge bosons. According to the conventional wisdom, this happens through the spontaneous breaking of gauge symmetry. Yet, gauge symmetries merely reflect a redundancy in the state description and therefore the spontaneous breaking can not be an essential ingredient. Indeed, as already shown by Higgs and Kibble, the mechanism can be explained in terms of gauge invariant variables, without invoking spontaneous symmetry breaking. In this paper, we present a general discussion of such gauge invariant (...)
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  • The Problem of Time.Karim P. Y. Thebault - forthcoming - In Eleanor Knox & Alastair Wilson (eds.), Routledge Companion to the Philosophy of Physics. Routledge.
    The `problem of time' is a cluster of interpretational and formal issues in the foundations of general relativity relating to both the representation of time in the classical canonical formalism, and to the quantization of the theory. The purpose of this short chapter is to provide an accessible introduction to the problem.
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  • Conceptual Foundations of Yang–Mills Theories.Alexandre Guay - 2008 - Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 39 (3):687-693.
    Essay review of Gauging What’s Real: The Conceptual Foundations of Contemporary Gauge Theories R. Healey. Oxford University Press (2007). To be published in the Studies in History and Philosophy of Modern Physics, 39(3):687-693, 2008.
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  • Change in Hamiltonian General Relativity From the Lack of a Time-Like Killing Vector Field.J. Brian Pitts - 2014 - Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 47:68-89.
    In General Relativity in Hamiltonian form, change has seemed to be missing, defined only asymptotically, or otherwise obscured at best, because the Hamiltonian is a sum of first-class constraints and a boundary term and thus supposedly generates gauge transformations. Attention to the gauge generator G of Rosenfeld, Anderson, Bergmann, Castellani et al., a specially _tuned sum_ of first-class constraints, facilitates seeing that a solitary first-class constraint in fact generates not a gauge transformation, but a bad physical change in electromagnetism or (...)
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  • 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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