Seminarium Teorii Względności i Grawitacji

I will discuss the time problem in the framework of quantum fields on quantum spacetimes, considering the specific example of primordial gravitational waves propagating through a bouncing quantum Friedman universe. We will see that the dynamical variables, such as the scale factor or the amplitude of a gravitational wave, obtained from different internal clocks, evolve differently. These expectation values (background evolution) and mode functions of operators (perturbations), irrespective of the clock chosen, converge to a unique evolution for large classically-behaving universes. This is the phase space domain in which unambiguous predictions can be made.