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The quantum theory and cosmological signature of loop quantum cosmology

Final Activity Report Summary - LQC (The quantum theory and cosmological signature of loop quantum cosmology)

The objectives of the project were the development and application of the theory of loop quantum gravity with emphasis on its consequences during the earliest moments of the universe. This led to the theory of loop quantum cosmology. Without having a complete understanding of quantum gravity in the early universe, the current theories of physics estimate that it began as an infinitely hot single point, known as the big-bang singularity. It is generally believed that this singularity represents a breakdown of the current theories of physics, principally of the gravitational theory of general relativity. A quantum theory of gravity would combine the theories of quantum mechanics and general relativity and would thus be expected to give a better description of the early universe.

Loop quantum cosmology was mainly developed at Penn State University, beginning in 2001, by Martin Bojowald as well as others including the fellow. A major result was discovered in 2006 by Abhay Ashtekar, Tomasz Pawlowski, and Parampreet Singh. They showed that loop quantum cosmology predicted that there was no big-bang singularity; instead, the universe bounced when it became extremely hot. This implied that our universe was collapsing at some early stage until it bounced and then became the expanding universe we see today.

During the project, the fellow, along with collaborators at the host institute and at Penn State University, helped to develop this idea of the bouncing universe and ensure that the results were robust under different possible scenarios. In particular, the big-bang singularity was removed in loop quantum cosmology regardless of the shape of the universe (refer to 1, 2), as well as if it did not look the same in all directions (4). These results gave evidence that loop quantum cosmology provided a good description of the early universe that did not suffer from infinite singularities. By the reporting period there was ongoing work at research institutes around the world to determine if we could observe any effects that might rise from a universe that bounced at some early time.

Black holes are exotic former stars where, like the big-bang singularity, current theories of physics predict an infinite singular point at the centre. They provided another interesting case to determine what a quantum theory of gravity would predict. Thus the fellow, along with Christian Boehmer at the host institute (5), applied loop quantum gravity and found that inside a black hole a strange exotic universe, that was free of a singularity, existed. Once again, loop quantum gravity was shown to remove the infinite singularity, a result that was highly significant. The outcomes of this article were a featured online news item in the 'New Scientist' publication (6).

This final report references are the following:

1. K. Vandersloot, loop quantum cosmology and the k = -1 RW model, Physical Review D 75:023523, 2007.
2. A. Ashtekar, P. Singh, K. Vandersloot, loop quantum cosmology of k=1 FRW models, Physical Review D 75:024035, 2007.
4. D. W. Chiou, K. Vandersloot, the behavior of non-linear anisotropies in bouncing Bianchi I models of loop quantum cosmology, Physical Review D 76:084015, 2007.
5. C. G. Boehmer, K. Vandersloot, loop quantum dynamics of the Schwarzschild interior, Physical Review D 76:104030, 2007.
6. M. Inman, black holes may harbour their own universes, http://space.newscientist.com/article/dn12853-black-holes-may-harbour-their-own-universes.html.