Theory HEP Seminar

Perfect bounce in quantum cosmology

Steffen Gielen

Imperial College, Perimeter Institute & CITA

The big bang singularity demands resolution, most likely by quantum effects, but it is unclear whether singularity resolution can be understood without knowing full quantum gravity. I will present a simple model, based only on general relativity coupled to radiation and to scalar fields, in which the big crunch/big bang is avoided by a process similar to quantum tunneling: a large, collapsing Lorentzian universe can make a transition to a large, expanding Lorentzian universe without encountering a singularity. No Wick rotation to Euclidean time is needed, but complex solutions play an important role as semiclassical descriptions. Regularity of this “perfect bounce” puts constraints on spatial curvature and anisotropies, which may help resolve fundamental questions in cosmology. I will also show how linear and nonlinear inhomogeneities evolve regularly across the classical singularity.