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marcus

Science Advisor

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http://arxiv.org/abs/0806.0397

**The Self-Organized de Sitter Universe**

J. Ambjorn, J. Jurkiewicz, R. Loll

7 pp, 1 figure, entry to 2008 GRF essay competition, honourable mention

(Submitted on 2 Jun 2008)

"We propose a theory of quantum gravity which formulates the quantum theory as a nonperturbative

**path integral**, where each spacetime history appears with a

**weight**given by the exponentiated Einstein-Hilbert action of the corresponding causal geometry. The path integral is

**diffeomorphism-invariant**(only geometries appear) and

**background-independent**. The theory can be investigated by computer simulations, which show that a

**de Sitter universe emerges on large scales**. This emergence is of an entropic, self-organizing nature, with the weight of the Einstein-Hilbert action playing a minor role. Also the

**quantum fluctuation**s around this de Sitter universe can be studied quantitatively and

**remain small until one gets close to the Planck scale**. The structures found to describe Planck-scale gravity are reminiscent of certain aspects of condensed-matter systems."

This is the first time that a whole smooth spacetime continuum (not put in by hand at the beginning) has emerged as the weighted average in a kind of Feynman path integral. (combining much variety of irregular spacetimes, whose unsmoothness cancels out in the average.) It is obviously a landmark achievement. But it comes at a time when OTHER significant results have also just appeared in other non-string QG research lines. Loop Quantum Cosmology, for instance.

To place it in context, I will fetch the four or five others constituing the MVP (most valuable paper) nominee list so far---we still have some three weeks to go before nominations are closed. If you have some suggestions, or comments on any of the papers, please contribute them to this thread.