Large classical universes emerging from quantum cosmology

TL;DR

This paper introduces a new class of solutions in quantum cosmology where the Universe naturally becomes large after the quantum bounce without requiring inflation, by leveraging a velocity parameter that induces acceleration.

Contribution

It presents a novel family of moving Gaussian solutions to the Wheeler-DeWitt equation that enable large classical universes to emerge from quantum models without inflation.

Findings

Large universes can arise from quantum cosmology without inflation.

The new solutions induce acceleration that enlarges the universe post-bounce.

Perturbations are free from transplanckian issues.

Abstract

It is generally believed that one cannot obtain a large Universe from quantum cosmological models without an inflationary phase in the classical expanding era because the typical size of the Universe after leaving the quantum regime should be around the Planck length, and the standard decelerated classical expansion after that is not sufficient to enlarge the Universe in the time available. For instance, in many quantum minisuperspace bouncing models studied in the literature, solutions where the Universe leave the quantum regime in the expanding phase with appropriate size have negligible probability amplitude with respect to solutions leaving this regime around the Planck length. In this paper, I present a general class of moving gaussian solutions of the Wheeler-DeWitt equation where the velocity of the wave in minisuperspace along the scale factor axis, which is the new large parameter introduced in order to circumvent the abovementioned problem, induces a large acceleration around the quantum bounce, forcing the Universe to leave the quantum regime sufficiently big to increase afterwards to the present size, without needing any classical inflationary phase in between, and with reasonable relative probability amplitudes with respect to models leaving the quantum regime around the Planck scale. Furthermore, linear perturbations around this background model are free of any transplanckian problem.