Can a man-made Universe be created by quantum tunneling without an initial singularity?

Abstract

Essentially all modern particle theories suggest the possible existence of a false vacuum state – a metastable state with an energy density that cannot be lowered except by means of a very slow phase transition. Inflationary cosmology makes use of such a state to drive the expansion of the big bang, allowing the entire observed universe to evolve from a very small initial mass. A sphere of false vacuum in our present universe, if larger than a certain critical mass, could inflate to form a new universe which would rapidly detach from its parent. A false vacuum bubble of this size, however, cannot be produced classsically unless an initial singularity is present from the outset. We therefore explore the possibility that a bubble of subcritical size, which classically would evolve to a maximum size and collapse, might instead tunnel through a barrier to produce a new universe. We estimate the tunneling rate using semiclassical quantum gravity, and discover some interesting ambiguities in the formalism.