Loop quantum gravity/cosmology is one of the newer and leading options for having a scientific explanation of the origin of the universe/multiverse. I found a very interesting paper by Julien Grain with the Institut d’Astrophysique Spatiale, CNRS/Université in Paris, France.
The main requirement for a quantum gravity proposal is to solve for the pathological big bang singularities and this can be checked by computing the global evolution of the Universe in a quantum cosmological setting. However, it should be stressed out that such a global evolution cannot be probed directly as one cannot extract himself from the Universe to ‘see’ how it evolves in its primary ages. We are stuck inside the Universe and, from the inside, we are able to probe the physics of the early Universe via the Cosmic Microwave Background (CMB) anisotropies. The origin of such anisotropies are cosmological perturbations produced during a phase of accelerated expansion dubbed cosmic inflation… (See paper).
The primordial Universe can be used as a laboratory to set constraints on quantum gravity. In the framework of Loop Quantum Cosmology, we show that such a proposal for quantum gravity not only solves for the big bang singularity issu but also naturally generates ination. Thanks to a quantitative computation of the amount of gravity waves produced in the loopy early Universe, we show that future cosmological datas on the polarized anisotropies of the Cosmic Microwave Background can be used to probe LQC model of the Universe.