Cited by 1,951Noncommutative and Quantum Gravity TheoriesRelativity and Gravitational TheoryBlack Holes and Theoretical Physics

Background independent quantum gravity: a status report

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Ashtekar, Abhay, Lewandowski, Jerzy·2004·Classical and Quantum Gravity

Abstract

The goal of this review is to present an introduction to loop quantum gravity—a background-independent, non-perturbative approach to the problem of unification of general relativity and quantum physics, based on a quantum theory of geometry. Our presentation is pedagogical. Thus, in addition to providing a bird's eye view of the present status of the subject, the review should also serve as a vehicle to enter the field and explore it in detail. To aid non-experts, very little is assumed beyond elements of general relativity, gauge theories and quantum field theory. While the review is essentially self-contained, the emphasis is on communicating the underlying ideas and the significance of results rather than on presenting systematic derivations and detailed proofs. (These can be found in the listed references.) The subject can be approached in different ways. We have chosen one which is deeply rooted in well-established physics and also has sufficient mathematical precision to ensure that there are no hidden infinities. In order to keep the review to a reasonable size, and to avoid overwhelming non-experts, we have had to leave out several interesting topics, results and viewpoints; this is meant to be an introduction to the subject rather than an exhaustive review of it.

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Registry

Crossref · 10.1088/0264-9381/21/15/r01

Cites

268 of 268 references verified0 citation errors · 0 not checkable

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  • LQG is a proposal for implementing the quantization program established by Dirac, Wheeler, and DeWitt.

    “LQG is a proposal for the implementation of the quantization program established in the 1960s by Dirac, Wheeler, and DeWitt, among others (for recent reviews see [35, 356, 323]).”

    From The Spin-Foam Approach to Quantum Gravity (2013) · cites this paper as [35]

  • In loop quantum gravity, spatial geometrical operators such as area, volume, and length have been constructed on the kinematical Hilbert space and possess discrete spectra.

    “One of the celebrated results of loop quantum gravity ͑LQG͒ is the discreteness of the spectrum of geometrical operators such as length, area, and volume operators.”
  • The original model of [2,3] and the variant pointed out in [11] appear as limiting γ→0 and γ→∞ cases, respectively.

    “The original model of [2, 3] and the variant pointed out in [11] appear as limiting γ → 0 and γ → ∞ cases, respectively.”

    From LQG vertex with finite Immirzi parameter (2008) · cites this paper as [11]

  • All these models are defined by the same vertex, the square of the SU(2) Wigner 15j symbol; they differ for the class of boundary states considered and their measure in the spinfoam sum.

    “All these models ([2, 3, 11, 12],) are defined by the same vertex, namely the square of the SU (2) Wigner 15 j symbol; they differ for the class of boundary states considered and their measure in the spinfoam sum.”

    From LQG vertex with finite Immirzi parameter (2008) · cites this paper as [11]

  • The constraints can equivalently be solved using coherent states, yielding the same result as the master-constraint technique.

    “In [11], it was shown that these constraints can equivalently be solved using a different technique, based on coherent states, yielding the same result.”

    From LQG vertex with finite Immirzi parameter (2008) · cites this paper as [11]

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Cites

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Research works printed but not linked: 5

  1. [26]26. Wisniewski J 2001 Symplectic structure from Holst action Preprint
  2. [67]67. Lewandowski J, Okolów A, Sahlmann H and Thiemann T 2003 Uniqueness of the diffeomorphism invariant state on the quantum holonomy-flux algebra Preprint Spin networks
  3. [136]136. R150 Topical Review
  4. [177]177. Sahlmann H and Thiemann T 2002 Towards the QFT on curved spacetime limit of QGR: II. A concrete implementation Preprint gr-qc/0207031 · arXiv
  5. [215]215. Okolw A 2004 Representations of quantum geometry PhD Thesis University of Warsaw

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Authors
Ashtekar, A., & Lewandowski, J.
Affiliations
  • Pennsylvania State University (US)
  • Max Planck Society (DE)
Venue
Classical and Quantum Gravity
Published
2004-07-10
Volume
21
Issue
15
Pages
R53-R152
ISSN
  • 0264-9381 (ISSN-L)
  • 1361-6382
OpenAlex
W2070707213
Cited by
1,951
References
268
Citations by year
2026: 81 · 2025: 145 · 2024: 97 · 2023: 70 · 2022: 64 · 2021: 75 · 2020: 68 · 2019: 79 · 2018: 62 · 2017: 72 · 2016: 97 · 2015: 68 · 2014: 91 · 2013: 88 · 2012: 107
FWCI
64.56
Type
journal article
Language
en
Open access
Locations
  • Classical and Quantum Gravity (publishedVersion)
  • arXiv (Cornell University) (publishedVersion)
  • CERN Document Server (European Organization for Nuclear Research) (submittedVersion)
  • Max Planck Institute for Plasma Physics (submittedVersion)
  • Max Planck Digital Library (submittedVersion)
  • MPG.PuRe (Max Planck Society) (submittedVersion)
  • arXiv (Cornell University)
Funders
  • National Science Foundation (0090091)
  • Alexander von Humboldt-Stiftung
  • Pennsylvania State University
Topics
  • Physical Sciences › Physics and Astronomy › Statistical and Nonlinear Physics › Noncommutative and Quantum Gravity Theories
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Relativity and Gravitational Theory
  • Physical Sciences › Physics and Astronomy › Nuclear and High Energy Physics › Black Holes and Theoretical Physics
Keywords
loop quantum gravity, background independence, quantum geometry, unification of quantum mechanics and general relativity, non-perturbative quantum gravity

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