# Abstracts Colloquium Febuary 06, 2013

**Claus Kiefer** (University Köln)

*Can effects of Quantum Gravity be observed in the cosmic microwave background?*

In any approach to quantum gravity, it is crucial to look for observational effects. In my talk, I discuss how quantum gravitational contributions to the anisotropy spectrum of the cosmic microwave background arise in the

framework of quantum geometrodynamics (Wheeler-DeWitt equation). From the present non-observation of these contributions, we find a constraint on the Hubble parameter of inflation. I also compare these results with the predictions from loop quantum cosmology.

Literature:

C. Kiefer and M. Krämer, Phys. Rev. Lett. 108, 021301 (2012)

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**Steffen Gielen** (Perimeter Institute for Theoretical Physics, Waterloo, Kanada)

*Observer dependent spacetimes*

I review several instances in gravitational physics where spacetime geometry can be described using fields of observers, normalised timelike vectors. Such an observer field can be associated to a choice of foliation in canonical gravity, and leads to a spontaneous breaking of local Lorentz covariance to a subgroup of rotations. The geometry is best understood by formulating GR as a theory on observer space, the space of all observers at different points in spacetime. After detailing this construction and a related one for theories with a fixed foliation such as Horava-Lifshitz gravity, I explain how observer spaces can also encode more general descriptions of spacetime geometry, such as Finsler geometry, and can be a useful general framework for studies of quantum gravity phenomenology.

Literature: S. Gielen and D. K. Wise, Gen. Rel. Grav. 44 (2012) 3103-3109

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**Sven Herrmann** (ZARM, University Bremen)

*Testing fundamental physics with matter wave interferometry in the drop tower and in space *

Matter wave interferometry today is an established tool to perform

precision measurements in fundamental physics. One of the main limiting factors in such experiments is the limited free evolution time available

to matter waves in a laboratory setup. Thus, the extended free fall

time which can be achieved in a microgravity environment (in the drop

tower or in a space based experiment) is expected to be of great benefit to future matter wave precision measurements. One interesting such test could be a test of the Universality of Free Fall using different species of ultra-cold, quantum degenerate atoms in a dual species matter wave interferometer.

In this talk I will present some of the recent progress achieved by

the QUANTUS collaboration towards interferometry at extended free fall times at the Bremen drop tower. n particular, I I will also discuss the perspectives of a test of the Universality of Free Fall with atoms not only in the drop tower but also in a satellite based mission.

The latter is currently studied by ESA, where the STE-QUEST mission, a quantum equivalence principle space test, is one candidate M-class mission within the cosmic vision programme.

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