Quantum Nature of the Big Bang

TL;DR

This paper demonstrates that in loop quantum cosmology, the big bang singularity is replaced by a deterministic big bounce, with scalar fields serving as internal clocks, and provides a rigorous construction of the quantum states and observables.

Contribution

It extends previous work by rigorously constructing the physical Hilbert space, Dirac observables, and demonstrating a deterministic quantum evolution through the big bounce.

Findings

The scalar field acts as an internal clock.

The big bang is replaced by a big bounce.

Quantum evolution remains deterministic across the Planck regime.

Abstract

Some long standing issues concerning the quantum nature of the big bang are resolved in the context of homogeneous isotropic models with a scalar field. Specifically, the known results on the resolution of the big bang singularity in loop quantum cosmology are significantly extended as follows: i) the scalar field is shown to serve as an internal clock, thereby providing a detailed realization of the `emergent time' idea; ii) the physical Hilbert space, Dirac observables and semi-classical states are constructed rigorously; iii) the Hamiltonian constraint is solved numerically to show that the big bang is replaced by a big bounce. Thanks to the non-perturbative, background independent methods, unlike in other approaches the quantum evolution is deterministic across the deep Planck regime.