Perturbations and observables in inhomogeneous cosmologies

• Applicant: Professor Dr. Matthias Bartelmann
• Subject Area: Astrophysics and Astronomy
• Term: from 2012 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 225630247

Is it possible that the apparently accelerated expansion of the Universe is not due to the repulsive effect of dark energy, but mimicked by the behaviour of a huge, underdense local environment? This question has often been addressed. A particularly suitable if idealised framework is provided by the class of Lemaître-Tolman-Bondi (LTB) solutions of General Relativity. Results achieved so far in this context seem to indicate that recent cosmological data rule out the hypothesis that we may be living in an inhomogeneous universe under certain restrictive assumptions, but are not in conflict with an LTB interpretation under more liberal conditions. We propose to extend existing studies in a five-fold way. We shall select those models from the LTB class that have a synchronous Big Bang. On this foundation, we shall then study systematically how the data allow our local cosmic environment to be structured, how linear structure formation proceeds in such models if couplings are allowed that have so far been neglected, how gravitational light deflection constrains LTB models, how temperature fluctuations in the cosmic microwave background must be interpreted and how non-linear structure formation proceeds. The results are expected to tighten the theoretical and empirical constraints on LTB models substantially.

• DFG Programme: Research Grants