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  • 1
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    Arrows of time in the bouncing universes of the no-boundary quantum state (2012)
    American Physical Society (APS)
    Details
    Publication Date: 2012-05-23
    Description: Author(s): James Hartle and Thomas Hertog We derive the arrows of time of our universe that follow from the no-boundary theory of its quantum state (NBWF) in a minisuperspace model. Arrows of time are viewed four-dimensionally as properties of the four-dimensional Lorentzian histories of the universe. Probabilities for these histories are p... [Phys. Rev. D 85, 103524] Published Tue May 22, 2012
    Keywords: Astrophysics & Cosmology
    Print ISSN: 0556-2821
    Electronic ISSN: 1089-4918
    Topics: Physics
    Published by American Physical Society (APS)
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  • 2
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    Local Observation in Eternal Inflation (2011)
    American Physical Society (APS)
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    Publication Date: 2011-04-09
    Description: Author(s): James Hartle, S. W. Hawking, and Thomas Hertog We consider landscape models that admit several regions where the conditions for eternal inflation hold. It is shown that one can use the no-boundary wave function to calculate small departures from homogeneity within our past light cone despite the possibility of much larger fluctuations on super h... [Phys. Rev. Lett. 106, 141302] Published Fri Apr 08, 2011
    Keywords: Gravitation and Astrophysics
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society (APS)
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  • 3
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    Anthropic bounds on Λ from the no-boundary quantum state (2013)
    American Physical Society (APS)
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    Publication Date: 2013-12-10
    Description: Author(s): James Hartle and Thomas Hertog We show that anthropic selection emerges inevitably in the general framework for prediction in quantum cosmology. There the predictions of anthropic reasoning depend on the prior implied by the universe’s quantum state. To illustrate this we compute the probabilities specified by the no-boundary wav... [Phys. Rev. D 88, 123516] Published Mon Dec 09, 2013
    Print ISSN: 0556-2821
    Electronic ISSN: 1089-4918
    Topics: Physics
    Published by American Physical Society (APS)
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  • 4
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    Stephen Hawking (1942-2018): Toward a complete understanding of the universe [Retrospectives] (2018)
    National Academy of Sciences
    Details
    Publication Date: 2018-05-23
    Description: Stephen Hawking overcame the limitations of a debilitating disease to make major contributions to science. He did this through remarkable persistence, determination, conviction, courage, and will. He was supported in this by his family, his students, and his colleagues. Stephen Hawking. Image courtesy of Alan Fersht (University of Cambridge, Cambridge,...
    Keywords: Retrospectives
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 5
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    One bubble to rule them all (2017)
    American Physical Society (APS)
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    Publication Date: 2017-06-06
    Description: Author(s): James Hartle and Thomas Hertog We apply the principles of quantum mechanics and quantum cosmology to predict probabilities for our local observations of a Universe undergoing false-vacuum eternal inflation. At a sufficiently fine-grained level, histories of the Universe describe a mosaic of bubble universes separated by inflation… [Phys. Rev. D 95, 123502] Published Mon Jun 05, 2017
    Keywords: Cosmology
    Print ISSN: 0556-2821
    Electronic ISSN: 1089-4918
    Topics: Physics
    Published by American Physical Society (APS)
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  • 6
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    Quantum transitions between classical histories (2015)
    American Physical Society (APS)
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    Publication Date: 2015-09-10
    Description: Author(s): James Hartle and Thomas Hertog In a quantum theory of gravity spacetime behaves classically when quantum probabilities are high for histories of geometry and field that are correlated in time by the Einstein equation. Probabilities follow from the quantum state. This quantum perspective on classicality has important implications.… [Phys. Rev. D 92, 063509] Published Tue Sep 08, 2015
    Keywords: Cosmology
    Print ISSN: 0556-2821
    Electronic ISSN: 1089-4918
    Topics: Physics
    Published by American Physical Society (APS)
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  • 7
    Electronic Resource
    Electronic Resource
    Simplical minisuperspace. III. Integration contours in a five-simplex model (1989)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 30 (1989), S. 452-460 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The no boundary proposal for the wave function of the universe is investigated in a minisuperspace model of pure gravity with cosmological constant. The model's four geometries consist of five four-simplices joined together to make the surface of a five-simplex from which one four-simplex face has been removed. The model is further simplified by symmetrically choosing all the interior edges of equal length and all the edges of the four-simplex boundary of equal length. The wave function is thus a function of a single boundary squared edge length and is specified by an integral over the single interior edge length. The analytic properties of the action in the space of complex edge lengths are exhibited, its classical extrema are calculated, and the possible contours of integration defining the wave function of the universe are discussed. A descending contour of constant imaginary action is proposed along which the integral defining the wave function is convergent and which predicts classical space-time in the late universe. This contour is the analog for the model of the conformally rotated contour appropriate to Euclidean sums over asymptotically flat space-times. The wave function is evaluated numerically for this contour both directly and by semiclassical methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.528410
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  • 8
    Electronic Resource
    Electronic Resource
    Solutions of the Regge equations on some triangulations of CP2 (1997)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 38 (1997), S. 2577-2586 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Simplicial geometries are collections of simplices making up a manifold together with an assignment of lengths to the edges that define a metric on that manifold. The simplicial analogs of the Einstein equations are the Regge equations. Solutions to these equations define the semiclassical approximation to simplicial approximations to a sum over geometries in quantum gravity. In this paper, we consider solutions to the Regge equations with a cosmological constant that give Euclidean metrics of high symmetry on a family of triangulations of CP2 presented by Banchoff and Kühnel. This family is characterized by a parameter p. The number of vertices grows larger with increasing p. We exhibit a solution of the Regge equations for p=2 but find no solutions for p=3. This example shows that merely increasing the number of vertices does not ensure a steady approach to a continuum geometry in the Regge calculus. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.531958
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  • 9
    Electronic Resource
    Electronic Resource
    Simplicial minisuperspace. II. Some classical solutions on simple triangulations (1986)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 27 (1986), S. 287-295 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The extrema of the Euclidean Regge gravitational action are investigated numerically for some closed, compact, four-dimensional simplicial manifolds with topologies S4, CP2, and S2×S2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.527331
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  • 10
    Electronic Resource
    Electronic Resource
    Simplicial minisuperspace I. General discussion (1985)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 26 (1985), S. 804-814 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The use of the simplicial methods of the Regge calculus to construct a minisuperspace for quantum gravity and approximately evaluate the wave function of the state of minimum excitation is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.526571
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