Speaker
Steffen Gielen
(University of Sheffield)
Description
I will summarise some recent work illustrating a fundamental clash between requiring unitarity in quantum theories of gravity and the notion of general covariance: unitarity means well-defined evolution for arbitrarily long time, but as different notions of time may remain finite or infinite, e.g., on approach to a cosmological singularity, this may or may not require significant departures from classical evolution in the quantum theory. I will mostly focus on cosmological models but also discuss other scenarios, such as the black hole interior. I will also comment on how different approaches to quantization might offer different views on this question.
