Lam, Vincent and Esfeld, Michael (2012) A dilemma for the emergence of spacetime in canonical quantum gravity. [Preprint]
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Abstract
The procedures of canonical quantization of the gravitational field apparently lead to entities for which any interpretation in terms of spatiotemporal localization or spatiotemporal 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 nonspatiotemporal 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.
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Item Type:  Preprint  

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Keywords:  spacetime, emergence, quantum geometrodynamics, loop quantum gravity, quantum superposition, quantum entanglement, nonseparability, structural realism, local beables  
Subjects:  Specific Sciences > Physics > Cosmology Specific Sciences > Physics > Quantum Field Theory Specific Sciences > Physics > Quantum Mechanics Specific Sciences > Physics > Relativity Theory 

Depositing User:  Vincent Lam  
Date Deposited:  02 Apr 2012 11:58  
Last Modified:  02 Apr 2012 11:58  
Item ID:  9074  
URI:  http://philsciarchive.pitt.edu/id/eprint/9074 
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