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          Institute: MPI für Gravitationsphysik     Collection: Quantum Gravity and Unified Theories     Display Documents

ID: 206119.0, MPI für Gravitationsphysik / Quantum Gravity and Unified Theories
Euclidean and Lorentzian quantum gravity - lessons from two dimensions
Authors:Ambjörn, Jan; Nielsen, J. L.; Rolf, J.; Loll, Renate
Date of Publication (YYYY-MM-DD):1999
Title of Journal:Chaos, Solitons and Fractals
Issue / Number:2-3
Start Page:177
End Page:195
Copyright:Jahrbuch 2000, Copyright MPG 2000
Review Status:not specified
Audience:Not Specified
Intended Educational Use:No
Abstract / Description:No theory of four-dimensional quantum gravity exists as yet. In this situation the two-dimensional theory, which can be analyzed by conventional field-theoretical methods, can serve as a toy model for studying some aspects of quantum gravity. It represents one of the rare settings in a quantum-gravitational context where one can calculate quantities truly independent of any background geometry.

We review recent progress in our understanding of 2d quantum gravity, and in particular the relation between the Euclidean and Lorentzian sectors of the quantum theory. We show that conventional 2d Euclidean quantum gravity can be obtained from Lorentzian quantum gravity by an analytic continuation only if we allow for spatial topology changes in the latter. Once this is done, one obtains a theory of quantum gravity where space-time is fractal: the intrinsic Hausdorff dimension of usual 2d Euclidean quantum gravity is four, and not two. However, certain aspects of quantum space-time remain two-dimensional, exemplified by the fact that its so-called spectral dimension is equal to two.
External Publication Status:published
Document Type:Article
Communicated by:Hermann Nicolai
Affiliations:MPI für Gravitationsphysik/Quantum Gravity and Unified Theories
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