Martin Bojowald Professor of Physics 304A Whitmore Lab (physical address); 104 Davey Lab #256 (mailing address) University Park, PA 16802 Phone: +1 814-865-3502 Fax: +1 814-863-9608 Email: bojowald@gravity.psu.edu Personal webpage

The main aim of my current research is a deeper understanding of quantum gravity based on possible physical phenomena it implies, possibly leading to crucial tests of its theoretical ingredients. As an initiator of loop quantum cosmology, I apply the general techniques of loop quantum gravity to specific conditions such as those found in the early universe or in black holes. In both applications, classical descriptions by general relativity lead to a point, at the big bang or inside black holes, where spacetime becomes singular and the classical theory breaks down. Several models of loop quantum cosmology are being developed and studied in detail where such singularities do not occur; they are rather prevented by quantum effects giving rise to repulsive contributions to the gravitational force. Current research focuses on a detailed understanding of this process by physical and geometrical pictures as well as on generalizing such scenarios to more complicated situations.

In addition to providing a well-defined description of the universe at the big bang or of black holes, quantum gravity also implies small deviations from classical behavior on larger scales. For an evaluation and eventual comparison with observations these corrections, arising from several different effects, are currently being derived for effective equations of cosmological perturbation theory. This can constrain possible quantization choices which will help in pinning down specifics of a quantum theory of gravity. Moreover, extrapolating the equations of quantum gravity even further back in time gives us indications as to what the universe could have been like even before the big bang. While precise predictions are difficult in such long-term extrapolations, current models can already tell us about possible limitations to our knowledge of properties of a pre-big bang universe.