A dilemma for the emergence of spacetime in canonical quantum gravity

Lam, Vincent and Esfeld, Michael (2012) A dilemma for the emergence of spacetime in canonical quantum gravity. Studies in History and Philosophy of Modern Physics: Part B, 44 3: 286-293. doi:10.1016/j.shpsb.2012.03.003

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Author Lam, Vincent
Esfeld, Michael
Title A dilemma for the emergence of spacetime in canonical quantum gravity
Journal name Studies in History and Philosophy of Modern Physics: Part B   Check publisher's open access policy
ISSN 1355-2198
Publication date 2012-07-15
Year available 2013
Sub-type Article (original research)
DOI 10.1016/j.shpsb.2012.03.003
Open Access Status
Volume 44
Issue 3
Start page 286
End page 293
Total pages 8
Place of publication Oxford, United Kingdom
Publisher Pergamon
Collection year 2013
Language eng
Abstract The procedures of canonical quantization of the gravitational field apparently lead to entities for which any interpretation in terms of spatio-temporal localization or spatio-temporal extension seems difficult. This fact is the main ground for the suggestion that can often be found in the physics literature on canonical quantum gravity according to which spacetime may not be fundamental in some sense. This paper aims to investigate this radical suggestion from an ontologically serious point of view in the cases of two standard forms of canonical quantum gravity, quantum geometrodynamics and loop quantum gravity. We start by discussing the physical features of the quantum wave functional of quantum geometrodynamics and of the spin networks (and spin foams) of loop quantum gravity that motivate the view according to which spacetime is not fundamental. We then point out that, by contrast, for any known ontologically serious understanding of quantum entanglement, the commitment to spacetime seems indispensable. Against this background, we then critically discuss the idea that spacetime may emerge from more fundamental entities. As a consequence, we finally suggest that the emergence of classical spacetime in canonical quantum gravity faces a dilemma: either spacetime ontologically emerges from more fundamental non-spatio-temporal entities or it already belongs to the fundamental quantum gravitational level and the emergence of the classical picture is merely a matter of levels of description. On the first horn of the dilemma, it is unclear how to make sense of concrete physical entities that are not in spacetime and of the notion of ontological emergence that is involved. The second horn runs into the difficulties raised by the physics of canonical quantum gravity.
Keyword Spacetime
Quantum geometrodynamics
Loop quantum gravity
Quantum superposition
Quantum entanglement
Structural realism
Local beables
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ
Additional Notes In press, corrected proof - Available online 15 July 2012.

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Mathematics and Physics
Official 2013 Collection
School of Historical and Philosophical Inquiry
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Created: Wed, 22 Aug 2012, 10:43:58 EST by Dr Vincent Lam on behalf of School of Historical and Philosophical Inquiry