Resolution of Singularities in Quantum Gravity and Quantum Cosmology.

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Singularities arise in the context of general relativity like in black holes and at the Big Bang. They signal a breakdown of classical general relativity and the need for a quantum theory of gravity in order to obtain a more complete understanding. A lot of work for understanding these singularities has been done in simplified models (minisuperspace models) but it is far from clear whether these capture the relevant physics of full quantum gravity as such models often depend on additional ad-hoc assumptions whose fundamental justification is unclear. The goal of my PhD is to develop a more systematic and rigorous derivation of effective symmetry-reduced quantum cosmology models from proposed theories of quantum gravity such as group field theory (GFT) and loop quantum gravity (LQG). In particular the idea that a macroscopic universe is obtained from a "condensate" of a large number of interacting degrees of freedom of quantum geometry will be employed.