The next cosmology seminar takes place on Friday 14th of November, room E349 at 2:00pm. We will have the pleasure to listen to Lisa Mickel from the Institut d’Astrophysique de Paris (IAP, France).
At 2:00pm, room E349, Lisa Mickel will be talking about
Trajectories for a superposition quantum universe
In the quest to establish possible imprints of quantum gravity one can quantise the reduced FLRW phase space to obtain so-called minisuperspace models that should be understood as a low energy limit of a full quantum gravitational theory. For a minisuperspace model that uses a perfect fluid as internal time and an affine quantisation procedure one finds solutions for the wave function that correspond to bouncing universes, thus resolving the big bang singularity. Starting from such a bouncing minisuperspace model we will relax the assumption that the state of the quantum universe has to correspond to a single highly semiclassical state. Instead, we will consider a universe in a superposition of such states, in accordance with the superposition principle of quantum mechanics. We are then faced with the question of how to extract a semiclassical scale factor that can be connected to the classical evolution of GR from such a system. Here we propose to make use of the trajectory approach to quantum mechanics, which assigns a unique value to the scale factor at all times. We introduce this approach to quantum mechanics more generally and show how it can be used to describe a single state universe, before continuing to investigate trajectories obtained for the case of a biverse (superposition of two semiclassical states). These trajectories exhibit features that significantly differ from the single state case. Finally, we illustrate the treatment of tensor perturbations on a background given by a biverse trajectory and consider the implications of the existence of such a trajectory for the evolution of perturbations.