Uploaded May 2025 | Updated September 2026, 2 weeks ago
Speaker: Steffen Gielen (University of Sheffield)
Abstract: In trying to formulate quantum theories of gravity, we need to agree on which basic principles are expected as fundamental in the new theory. One of the most important properties of standard quantum mechanics is unitarity of time evolution. Quantum gravity is often expected or required to be unitary in some sense, although it is less clear what that means. I will explore different ways in which unitarity can be realised in quantum models of cosmology and black holes, and show that certain notions of unitarity (using the time coordinate of unimodular gravity) can lead to generic resolution of classical singularities, replacing them by quantum transitions from a past universe or into a future white hole.
Speaker: Steffen Gielen (University of Sheffield)
Abstract: In trying to formulate quantum theories of gravity, we need to agree on which basic principles are expected as fundamental in the new theory. One of the most important properties of standard quantum mechanics is unitarity of time evolution. Quantum gravity is often expected or required to be unitary in some sense, although it is less clear what that means. I will explore different ways in which unitarity can be realised in quantum models of cosmology and black holes, and show that certain notions of unitarity (using the time coordinate of unimodular gravity) can lead to generic resolution of classical singularities, replacing them by quantum transitions from a past universe or into a future white hole.
