Quantum Cosmological Models

TL;DR

This paper compares different quantum cosmological models, analyzing their initial conditions, naturalness, and limitations, including inflationary, bouncing, brane, and loop quantum cosmology approaches.

Contribution

It provides a comprehensive comparison of various quantum cosmological models and their initial condition proposals, highlighting their strengths and limitations.

Findings

Loop quantum cosmology offers alternative initial conditions.

Many models face fine-tuning and naturalness issues.

Limitations and difficulties are identified across models.

Abstract

We contrast the initial condition requirements of various contemporary cosmological models, including inflationary and bouncing cosmologies. Various proposals such as Hartle-Hawking's no boundary, or Tunnelling boundary conditions are assessed on grounds of naturalness and fine tuning. Alternatively a quiescent or ``time machine'' state is considered. Extensions to brane models are also addressed. Further ideas about universe creation from a meta-universe are outlined. We compare the recent loop quantum cosmology of Bojowald and coworkers with these earlier proposals. A number of possible difficulties and limitations are outlined.