Quantum Gravity

Modern physics rests on two basic frameworks, quantum theory and general relativity. Quantum gravity aims to unify these two frameworks into one consistent theory. One can expect that such a formulation delivers in particular a novel understanding of space and time as quantum objects.

I will give an introduction to some basic concepts in quantum gravity research and present possible models of quantum space time.

Thanks to the spectacular observational advances since the 1990s, a `standard model' of the early universe has now emerged. However, since it is based on quantum field theory in curved space-times, it is not applicable in the Planck era. Using techniques from loop quantum gravity, the theory can be extended over the 12 orders of magnitude in density and curvature from the onset of inflation all the way back to the Planck regime, providing us with a possible completion of the standard model.

Contrary to a wide-spread belief, the resulting pre-inflationary dynamics can have observational consequences for the longest wave length modes of cosmological perturbations. Thus, there is now an an interesting interplay between fundamental theory and observations. The talk will provide a broad overview of these results addressed to non-experts.

Web-links:

Viewpoint: A glance at the earliest universe; APS Physics Spotlighting Exceptional Research: http://physics.aps.org/articles/v5/142

U tube video

http://www.youtube.com/watch?v=IFcQuEw0oY8&feature=c4-overview&list=UUtOgK

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A renormalization group transformation implements a scale transformation while resetting the UV cut-off, so that the theories before and after the RG transformation contain the same degrees of freedom, but with a modified action. In Wilson's original proposal, the cut-off is reset by integrating out the degrees of freedom between the old and new cut-off. In recent years we have learned that, alternatively, one can decouple these degrees of freedom by means of local unitary transformations (disentanglers). The result is a reversible renormalization group flow, and an efficient description of many-body ground states. In this talk, I will show you pretty drawings and will use fancy names, such as "multi-scale entanglement renormalization ansatz" (MERA). MERA is currently studied as a possible lattice realization of the AdS/CFT correspondence. I will keep it simple.