Time in semiclassical gravity

Brout, R.; Venturi, G.

doi:10.1103/physrevd.39.2436

Cited by 126 publications

(215 citation statements)

References 9 publications

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“…Subsequently the approach was further analysed in order to justify the use of the mean matter energy to drive gravitation [14]. This was found to be true when non-adiabatic transitions (fluctuations) are negligible and the Universe is sufficiently far from the Planck scale.…”

Section: Introductionmentioning

confidence: 99%

The Born–Oppenheimer method, quantum gravity and matter

Kamenshchik

Tronconi

Venturi

2017

Class. Quantum Grav.

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Abstract. We illustrate and examine diverse approaches to the quantum matter-gravity system which refer to the Born-Oppenheimer (BO) method. In particular we first examine a quantum geometrodynamical approach introduced by other authors in a manner analogous to that previously employed by us, so as to include back reaction and non-adiabatic contributions. On including such effects it is seen that the unitarity violating effects previously found disappear. A quantum loop space formulation (based on a hybrid quantisation, polymer for gravitation and canonical for matter) also refers to the BO method. It does not involve the classical limit for gravitation and has a highly peaked initial scalar field state. We point out that it does not resemble in any way to our traditional BO approach. Instead it does resemble an alternative, canonically quantised, non BO approach which we have also previously discussed.

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Section: Introductionmentioning

confidence: 99%

The Born–Oppenheimer method, quantum gravity and matter

Kamenshchik

Tronconi

Venturi

2017

Class. Quantum Grav.

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“…[9], but here we want to employ the more systematic Born-Oppenheimer approach (see, for instance, Ref. [7,16]). First of all, we assume that the complete wavefunction factorizes into "gravitational" (ψ) and "matter" (χ) parts,…”

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confidence: 99%

“…Another method is to impose a large (space-time) symmetry prior to quantization, resulting in a so called mini-(or midi-) superspace for a finite (or discrete) number of canonical variables [5,6]. In the latter approach to quantum gravity there is no time and one expects that a time variable can be identified by resorting to the semiclassical approximation [7].…”

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confidence: 99%

On time evolution of quantum black holes

Casadio

2001

Physics Letters B

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The time evolution of black holes involves both the canonical equations of quantum gravity and the statistical mechanics of Hawking radiation, neither of which contains a time variable. In order to introduce the time, we apply the semiclassical approximation to the Hamiltonian constraint on the apparent horizon and show that, when the backreaction is included, it suggests the existence of a long-living remnant, similarly to what is obtained in the microcanonical picture for the Hawking radiation.Key words: black holes, Hawking effect, microcanonical ensemble, semiclassical approximation, quantum gravity PACS: 04.70.-s, 04.70.Dy, 04.60.-m A longstanding issue in theoretical physics is how to quantize Einstein gravity. Since in the theory there are constraints whose algebra contains structure functions (which depend on the space-time coordinates), one can conceive (inequivalent [1]) manners of lifting the Hamiltonian and momentum constraints to quantum equations, thus hindering the formal solution to the problem. On a more physical ground, one might notice that it is relevant to have a quantum theory of gravity at our disposal only for systems with very strong (Planck size) gravitational fields, such as those one expects in the early stages of the Universe. Because of Hawking's discovery of black hole evaporation [2], one also expect that quantum (or semiclassical) gravity plays a role in determining the dynamics of the late stages in the life of collapsed objects.In a general situation, one has to deal with the infinite number of degrees of freedom of the gravitational field configurations which are physically distinguished only modulo coordinate transformations. This gives the constraints the form of functional differential equations, for which there is little hope of finding general solutions, and one then tries to reduce the number of degrees 1

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“…The above approach has been examined in detail within the context of a minisuperspace model with matter [5] with the view of understanding under what conditions matter follows gravity adiabatically and quantum cosmology leads to the usual physics (Schrodinger equation for matter and Einstein classical equations for gravity on scales larger than the Planckian). It was found that such w as the case in an in ationary scenario [7] and after ten or more Planck times the usual physics ensues.…”

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confidence: 99%

“…We n o w follow a procedure analogous to the one illustrated elsewhere [5] [ 6 ] and factorize the wave function as: (a ; f a n g ; f b n g ; ; f f n g ) = Y nñ ( a ; a n ; b n ; ; f n ) n ( a ; a n ;…”

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Semiclassical Gravity and Large-Scale Structure

Bertoni

Carretti

Finelli⋆

et al. 1995

Computational Mechanics ’95

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The possible cosmological e ects of primordial non{adiabatic uctuations in the matter{gravity quantum system are explored. In particular, both the metric and a scalar matter eld are expanded around their homogeneous values and the corrections induced on the scalar eld uctuation spectrum by the non{adiabatic terms are perturbatively estimated. Finally, results of a preliminary numerical simulation to investigate the e ects on large{scale structure formation are presented.The invariance of the Einstein action under arbitrary space{time transformations has as a consequence that time does not appear in the corresponding Hamiltonian formulation and such a feature is maintained in the canonical quantization of gravity within the superspace approach [ 1 ] [2].It has been observed, however, that the introduction of matter allows one to also introduce the concept of time: time parametrizes how matter follows gravity. In particular, it has been noted that the semiclassical wave function for gravity provides a parametrization for the evolution of matter in which the latter follows the former adiabatically [3] [ 4 ].In order to illustrate the above the matter{gravity w a v e function is factorized into two parts: one involving only gravitational degrees of freedom and the other involving both the gravitational and the matter degrees of freedom. Correspondingly, the Wheeler{De Witt (WD) equation in which time is absent is split into two pieces: one describing gravitation in an e ective potential given by the mean energy{momentum tensor of matter and the other describing the matter whose evolution is parametrized by time which is derived from the semiclassical approximation to the gravitational wave function [4]. The above is contingent on the hypothesis that the Planck mass is much larger than the mass of any matter eld or any i n v erse length scale used to describe matter.

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Time in semiclassical gravity

Cited by 126 publications

References 9 publications

The Born–Oppenheimer method, quantum gravity and matter

The Born–Oppenheimer method, quantum gravity and matter

On time evolution of quantum black holes

Semiclassical Gravity and Large-Scale Structure

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