Joint cosmology seminar at MIT:

Tuesday, March 14, 2017, 2:30 pm

Cosman Seminar Room

Center for Theoretical Physics

Building 6C, Room 6C-442

Massachusetts Institute of Technology

Refreshments at 2:00 in the same room

**Real time quantum cosmology**

Jean-Luc Lehners

Max-Planck-Institute for Gravitational Physics

Abstract:

I will revisit the path integral approach to quantum cosmology, from the viewpoint of the real Lorentzian path integral rather than the often-employed Euclidean version. At least in simple minisuperspace settings, Picard-Lefshetz theory allows one to define the path integral unambiguously, and selects the relevant saddle points. Comparing with the canonical approach, this allows one to single out a unique solution of the Wheeler-De Witt equation. If one imposes no-boundary initial conditions, the resulting weighting of the wave function favors large values of the cosmological constant, in agreement with Vilenkin's tunneling proposal but in contrast to the Hartle-Hawking prescription. Within the framework described here one can also describe quantum transitions between contracting and expanding universes. I will describe two examples of such potential quantum resolutions of classical big crunch singularities.