Definition of a time variable with entropy of a perfect fluid in canonical quantum gravity

Cianfrani, Francesco; Montani, Giovanni; Zonetti, Simone

doi:10.1088/0264-9381/26/12/125002

Cited by 8 publications

(8 citation statements)

References 20 publications

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“…7 However, Brown and Kuchař [29] have modeled a dust-filled universe by using a collection of scalar fields, of which one, say T , when the classical equations of motion are satisfied, is linear in the proper time along particle worldlines. This model has been studied more recently by several authors from the point of view of the relational formalism [33,34,46,47] (see also [30,31]).…”

Section: Discussionmentioning

confidence: 99%

“…Clearly, the idea of incorporating an observer's clock into our model is in some way akin to the notion of a material reference frame, which has been widely studied (see, for example [1,2,7,[29][30][31][32][33][34][35]). We think that the implementation of this general idea described below differs in important respects from others to be found in the literature, and will return to this point in section V.…”

Section: Rovellimentioning

confidence: 99%

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Time evolution in quantum cosmology

Lawrie

2011

Phys. Rev. D

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A commonly adopted relational account of time evolution in generally-covariant systems, and more specifically in quantum cosmology, is argued to be unsatisfactory, insofar as it describes evolution relative to observed readings of a clock that does not exist as a bona fide observable object. A modified strategy is proposed, in which evolution relative to the proper time that elapses along the worldline of a specific observer can be described through the introduction of a `test clock', regarded as internal to, and hence unobservable by, that observer. This strategy is worked out in detail in the case of a homogeneous cosmology, in the context of both a conventional Schrodinger quantization scheme, and a `polymer' quantization scheme of the kind inspired by loop quantum gravity. Particular attention is given to limitations placed on the observability of time evolution by the requirement that a test clock should contribute only a negligible energy to the Hamiltonian constraint. It is found that suitable compromises are available, in which the clock energy is reasonably small, while Dirac observables are reasonably sharply defined.Comment: 21 pages, no figures; minor revisions and added references; matches version in Phys Rev

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Section: Discussionmentioning

confidence: 99%

Section: Rovellimentioning

confidence: 99%

Time evolution in quantum cosmology

Lawrie

2011

Phys. Rev. D

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“…This problem was interestingly addressed in [1,4,24], where the relation between defining a time and defining a reference frame in quantum gravity are related concepts. For some attempts to characterize the time variable as a relational clock having peculiar properties, like a monotonic behavior, see [25,26]. However, one of the most interesting points of view on this topic, different from the one here proposed, is the so-called multitime approach [27], in which it is emphasized how the gravitational field has to be separated into its two real physical degrees of freedom, while the remaining part of the space geometry labels the evolution.…”

Section: Physical Grounds and Motivationmentioning

confidence: 93%

Nonsingular cosmology from evolutionary quantum gravity

2014

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We provide a cosmological implementation of the evolutionary quantum gravity, describing an isotropic Universe, in the presence of a negative cosmological constant and a massive (preinflationary) scalar field. We demonstrate that the considered Universe has a nonsingular quantum behavior, associated to a primordial bounce, whose ground state has a high occupation number. Furthermore, in such a vacuum state, the super-Hamiltonian eigenvalue is negative, corresponding to a positive emerging dust energy density. The regularization of the model is performed via a polymer quantum approach to the Universe scale factor and the proper classical limit is then recovered, in agreement with a preinflationary state of the Universe. Since the dust energy density is redshifted by the Universe deSitter phase and the cosmological constant does not enter the ground state eigenvalue, we get a late-time cosmology, compatible with the present observations, endowed with a turning point in the far future.

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“…For what regards the Schutz Hamiltonian, it has to be derived in a Dirac manner [21] given that from (3) one obtains a number of second class constraints φ α = 0. Solving those constraints, as prescribed by the Dirac theory, leads to the fluid's Hamiltonian [15]…”

Section: The Schutz Fluid As a Viable Clock In Quantum Gravitymentioning

confidence: 99%

Specific entropy as a clock for the evolutionary quantization of the isotropic Universe

Campolongo

Montani

2020

Eur. Phys. J. C

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In this paper, we analyze the dynamics of an isotropic closed Universe in presence of a cosmological constant term and we compare its behavior in the standard Wheeler–DeWitt equation approach with the one when a Lagrangian fluid is considered in the spirit of the Kuchar–Brown paradigm. In particular, we compare the tunnelling of the Universe from the classically forbidden region to the allowed one, showing that considering a time evolution deeply influences the nature of the model. In fact, we show that in the presence of the Lagrangian fluid, the cosmological singularity is restored both in the classical and the quantum regime. However, in the quantum regime the singularity is probabilistically suppressed for some energy eigenvalues and in the case the latter is equal to zero one recovers the standard WDW case. Finally, we introduce a cut-off physics feature in the Minisuperspace by considering a Polymer quantum mechanical approach limiting our attention to the semi-classical dynamics mainly (the quantum treatment is inhibited by the non-local nature of the Hamiltonian operator). We show that the singularity is again removed, like in the fluid-free model, and a bouncing cosmology emerges so that the present model could mimic a cyclic cosmology.

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Definition of a time variable with entropy of a perfect fluid in canonical quantum gravity

Cited by 8 publications

References 20 publications

Time evolution in quantum cosmology

Time evolution in quantum cosmology

Nonsingular cosmology from evolutionary quantum gravity

Specific entropy as a clock for the evolutionary quantization of the isotropic Universe

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