
#19
Nov2204, 10:18 PM

P: 134





#20
Dec804, 07:33 PM

Astronomy
Sci Advisor
PF Gold
P: 22,803

today there were two that appeared. by Daniele Oriti and by V.Husain and O.Winkler. In both cases the titles of the papers are virtually identical to those of the talks given at the Halloween conference at perimeter 1. http://arxiv.org/grqc/0412035 The Feynman propagator for quantum gravity: spin foams, proper time, orientation, causality and timelessordering Daniele Oriti 8 pages; to appear in the Proceedings of the DICE 2004 Workshop "From Decoherence and Emergent Classicality to Emergent Quantum Mechanics" "We discuss the notion of causality in Quantum Gravity in the context of sumoverhistories approaches, in the absence therefore of any background time parameter. In the spin foam formulation of Quantum Gravity, we identify the appropriate causal structure in the orientation of the spin foam 2complex and the data that characterize it; we construct a generalised version of spin foam models introducing an extra variable with the interpretation of proper time and show that different ranges of integration for this proper time give two separate classes of spin foam models: one corresponds to the spin foam models currently studied, that are independent of the underlying orientation/causal structure and are therefore interpreted as acausal transition amplitudes; the second corresponds to a general definition of causal or orientation dependent spin foam models, interpreted as causal transition amplitudes or as the Quantum Gravity analogue of the Feynman propagator of field theory, implying a notion of ''timeless ordering''." * 2. http://arxiv.org/grqc/0412039 Quantum black holes Viqar Husain, Oliver Winkler 4 pages "Using a recently developed quantization of spherically symmetric gravity coupled to a scalar field, we give a construction of horizon operators that allow a definition of general, fully dynamical quantum black holes. These operators capture the intuitive idea that classical black holes are defined by the presence of trapped surfaces, that is surfaces from which light cannot escape outward. They thus provide a mechanism for classifying quantum states of the system into those that describe quantum black holes and those that do not. We find that quantum horizons fluctuate, confirming longheld heuristic expectations. We also give explicit examples of quantum black hole states. The stage is thus set for addressing all the puzzles of black hole physics in a fully quantized dynamical setting." * 


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