A dilemma for the emergence of spacetime in canonical quantum gravity

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 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
Keywords Spacetime   Emergence   Quantum geometrodynamics   Loop quantum gravity   Quantum superposition   Quantum entanglement   Non-separability   Structural realism   Local beables   Structural Realism   Metaphysics   Systems   Worlds   Time
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DOI 10.1016/j.shpsb.2012.03.003
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References found in this work BETA
What is Structural Realism?J. Ladyman - 1998 - Studies in History and Philosophy of Science Part A 29 (3):409-424.

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Citations of this work BETA
Disappearance and Emergence of Space and Time in Quantum Gravity.Daniele Oriti - 2014 - Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 46 (2):186-199.
The Entanglement Structure of Quantum Field Systems.Vincent Lam - 2013 - International Studies in the Philosophy of Science 27 (1):59 - 72.
The Deep Metaphysics of Quantum Gravity: The Seventeenth Century Legacy and an Alternative Ontology Beyond Substantivalism and Relationism.Edward Slowik - 2013 - Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 44 (4):490-499.

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