Schulz, Benjamin (2019): Quantum gravity and spacetime foam. Dissertation, LMU München: Faculty of Physics 

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Abstract
This thesis argues that Hawking's model on spacetime foam predicts, after several modifications, a cosmological constant of the observed order. Inconsistencies of Hawking's model that were pointed out by Christensen and Duff are removed. A mechanism is given that can be used to remove the Ostrogradski instability of the effective matter action. The modified spacetime foam model of Hawking describes a spacetime filled with a gas of microscopic black and wormholes. It is noted that particles which fly through such a spacetime are governed by different equations of motion than in vacuum, since they scatter with the Hawking radiation of the microscopic blackholes and they are additionally under a collective influence of the gravitational field on long time scales. Under the assumption that Hawking radiation restores any information that was removed by the blackholes, one can derive the Schrödinger equation at low energies if one puts a classical particle into the spacetime foam. The spacetime foam model implies topology changes of the spacetime during the expansion of the universe. It is argued that ordinary quantum field theory on Lorentzian spacetimes is incompatible with such changes since they give rise to singularities. It is proposed that if a stochastic model with nondifferentiable paths underlies quantum mechanics at small scales (the usual path integral formulation is restricted to differentiable paths) then this could be used near the singularities during a topology change of the spacetime.
Item Type:  Theses (Dissertation, LMU Munich) 

Keywords:  quantum gravity, Euclidean quantum gravity, cosmological constant, topology change in quantum gravity 
Subjects:  500 Natural sciences and mathematics 500 Natural sciences and mathematics > 530 Physics 
Faculties:  Faculty of Physics 
Language:  English 
Date of oral examination:  15. October 2019 
1. Referee:  Lüst, Dieter 
MD5 Checksum of the PDFfile:  db0014dfcd7cd1f855ccfb66b27332ce 
Signature of the printed copy:  0001/UMC 28270 
ID Code:  25592 
Deposited On:  18. Oct 2021 14:10 
Last Modified:  18. Oct 2021 14:10 