June 2021  Invited talk on the operational determination of the gravitational field in Einstein's theory and beyond. Geometric Foundations of Gravity 2021, Tartu, Estonia. 
March 2019  Talk on the deviation of structured test bodies. Annual meeting of the German Physical Society (DPG), TU Munich, Germany. 
October 2017  Invited talk on the gravitational compass and the mapping of the gravitational field. AEI colloquium, MPI for Gravitational Physics, Germany. 
November 2016  Invited talk on the measurement of the gravitational field in General Relativity. Relativity seminar, University of Cologne, Germany. 
September 2015  Invited talk on test body motion in gravity. Annual meeting of the Deutsche Mathematiker Vereinigung (DMV), University of Hamburg, Germany. 
March 2015  Talk on a unified framework for test body equations of motion in gravity. Annual meeting of the German Physical Society (DPG), TU Berlin, Germany. 
April 2014  Invited talk on the mapping of the gravitational field with multipolar techniques. 558th WEHereausSeminar on the Strong Gravity Regime of Black Holes and Neutron Stars, Physikzentrum Bad Honnef, Bad Honnef, Germany. 
March 2014  Talk on probing the gravitational field with test bodies. Annual meeting of the German Physical Society (DPG), HU Berlin, Germany. 
June 2013  Talk on the motion of test bodies in theories with nonminimal coupling. GermanIsraeli Foundation for Scientific Research and Development (GIF) workshop, University of Bremen, Germany. 
February 2013  Talk on covariant equations of motion for test bodies in gravitational theories with general nonminimal coupling. Annual meeting of the German Physical Society (DPG), University of Jena, Germany. 
February 2013  Talk on multipolar approximation schemes for extended test bodies. 524th WEHereausSeminar on the Equations of Motion in Relativistic Gravity, Physikzentrum Bad Honnef, Bad Honnef, Germany. 
April 2012  Invited talk on the motion of extended bodies in General Relativity. CENTRA / Instituto Superior Tecnico, Lisbon, Portugal. 
March 2012  Testing gravity theories with multipolar techniques. Inaugural meeting of the research training group "Models of Gravity", University of Bremen, Germany. 
February 2012  Talk on supplementary conditions in general relativistic multipolar approximation schemes. Annual meeting of the German Physical Society (DPG), University of Goettingen, Germany. 
May 2011  Invited talk on the problem of motion in General Relativity. LeibnizInstitute for Astrophysics (AIP), Potsdam, Germany. 
February 2011  Talk on the equations of motion in General Relativity. 3rd GCOE International Symposium, Astronomical Institute, Tohoku University, Sendai, Japan. 
September 2010  Talk on the motion of extended bodies in General Relativity and the history of multipolar approximation schemes. Astronomical Institute, Tohoku University, Sendai, Japan. 
March 2010  Invited talk on the motion of extended bodies in General Relativity. Annual meeting of the German Physical Society (DPG), University of Bonn, Germany. 
October 2009  Talk on the motion of extended bodies in General Relativity. ZARM, University of Bremen, Germany. 
July 2009  Talk on multipolar approximation schemes and the motion of extended bodies in General Relativity. Institute of Theoretical Physics, University of Cologne, Germany. 
March 2009  Talk on the motion of extended bodies in General Relativity. SFB/TR7 Meeting, 16  17 March, 2009, University of Jena, Germany. 
December 2008  The problem of motion and the use of multipolar approximation schemes in gravity. 24th Texas Symposium on Relativistic Astrophysics, Vancouver, Canada, December 8  12, 2008. 
December 2008  Multipolar approximation techniques and their use in astrophysics and cosmology. High Energy Theory and Astrophysics Seminar at the Department of Physics, University of Utah, USA. 
December 2008  Probing the nature of space and time. Nuclear and Particle Theory seminar at the Department of Physics and Astronomy, University of Iowa, USA. 
November 2008  The problem of motion and the use of approximation schemes in relativistic astrophysics. Astronomy seminar at the Department of Physics and Astronomy, Iowa State University, USA. 
November 2007  Probing the nature of space and time. Colloquium at the Institute for Theoretical Astrophysics, University of Oslo, Norway. 
October 2007  Invited talk on the motion of test bodies with microstructure in gauge gravity models. Held at the conference on "Myron Mathisson: his life, work, and influence on current research", Stefan Banach International Mathematical Center, Warsaw, Poland. 
June 2007  Talk on the motion of test particles and the use of multipole formalisms in gravity. Held at the Institute for Theoretical Astrophysics, University of Oslo, Norway. 
May 2007  Talk on the problem of motion in alternative gravitational theories. Held at the Institute for Theoretical Physics, University of Geneva, Switzerland. 
October 2006  Talk on the Newtonian limit of higherorder gravity theories. Held at the cosmology seminar, Institute for Theoretical Astrophysics, University of Oslo, Norway. 
June 2006  Talk on the problem of motion in General Relativity. Held at the relativity group seminar, Institute for Theoretical Physics, University of Cologne, Germany. 
May 2006  Talk on the early history of the problem of motion. Held at the cosmology seminar, Institute for Theoretical Astrophysics, University of Oslo, Norway. 
December 2005  Talk on general relativistic approximation schemes and their application to cosmology. Cosmology 2005: A reality check, Copenhagen, Denmark. 
October 2005  Invited talk on general relativistic approximation schemes and the PN approximation in cosmology. University of Iowa, Iowa City, USA. 
September 2005  Invited talk on general relativistic approximation schemes and their application to cosmology. Institute for Theoretical Astrophysics, University of Oslo, Oslo, Norway. 
August 2005  Talk on the postNewtonian approximation and its application in cosmology. COSMO05, Bonn, Germany. 
June 2005  Invited talk on the postNewtonian approximation in cosmology and other approximation schemes in General Relativity. Korea Astronomy and Space Science Institute, Daejon, Korea. 
June 2005  Invited talk on approximation schemes in General Relativity and the first order cosmological postNewtonian approximation (1CPNA). Kyungpook National University, Taegu, Korea. 
June 2005  Talk on approximation schemes in cosmology. Held at PASCOS 2005, Gyeongju, Korea. 
May 2005  Talk on the postNewtonian approximation in cosmology and the history of approximation schemes in general relativity. Held at the astronomy seminar of the Korea Institute of Advanced Study (KIAS), Seoul, Korea. 
May 2005  Invited talk on alternative gravity theories and their application in modern cosmology. Held at the KIASAPCTPDMRC workshop on "The Dark Side of the Universe", KIAS, Seoul, Korea. 
May 2005  Talk on approximation schemes in general relativity. Held at the astronomy seminar of the Department of Physics and Astronomy, Iowa State University, USA. 
December 2004  Talk on the search for a gravitational solution of the dark matter and dark energy problem in cosmology. Held at the University of Utah, Salt Lake City, USA. 
December 2004  Poster presentation on the status and prospects of nonRiemannian cosmology. Texas Symposium 2004, Stanford University, USA.

November 2004  Popular talk on geometric concepts in gravitation and cosmology. Held at the seminar of the ISU Math Club, Iowa State University, Ames, USA. 
November 2004  Talk on trends in theoretical cosmology. Held at the GNP seminar, Iowa State University, Ames, USA. 
November 2004  Invited talk on the search for a gravitational solution of the dark matter and dark energy problem in cosmology. Held at University of Iowa, Iowa City, USA. 
October 2004  Invited talk on the status of NonRiemannian Cosmology (NRC) and discussion of the impact of current cosmological observations on theoretical model building. Held at Korean Institute for Advanced Study (KIAS), Seoul, South Korea. 
October 2004  Invited talk on current theoretical landscape in cosmology with particular emphasis on the status of NonRiemannian Cosmology (NRC). Brief discussion of recent results regarding the type Ia supernovae, Xray cluster, and FRIIb radio galaxy measurements in the context of a nonstandard cosmological model. Held at Ewha Womans University, Seoul, South Korea. 
October 2004  Invited talk on recent developments in cosmology with particular emphasis on the status of dark matter and dark energy. Discussion of the implications of these concepts on cosmological model building. Discussion of some recent results regarding the type Ia supernovae, Xray cluster, and FRIIb radio galaxy measurements in the context of a nonstandard cosmological model. Held at Beijing Normal University, Beijing, P.R. of China. 
September 2004  Talk on the current theoretical landscape in cosmology. Held at the astronomy seminar of the Department of Physics and Astronomy, Iowa State University, USA. 
September 2004  Status and prospects of nonRiemannian cosmology (NRC). Held at COSMO04, Toronto, Canada.[ pdf ] 
February 2004  Brief review of the current status of nonRiemannian cosmology (NRC). Latest results from SNIa for a nonstandard model. Held at the 6th UCLA Symposium on the sources and detection of Dark Matter and Dark Energy in the universe , Marina Del Rey, CA, USA.[ pdf ] 
January 2004  A rather broad brushed overview of the advancements in building and testing nonRiemannian cosmological models. In particular I focus on the developments within the framework of metricaffine gravity (MAG) and one of its special cases, the socalled WeylCartan spacetime. Held at the astronomy seminar of the Department of Physics and Astronomy, Iowa State University, USA.[ pdf ] 
December 2002  Talk on the primordial synthesis of light elements with focus on the production of helium4. Held at the seminar of the Graduiertenkolleg Scientific Computing, University of Cologne, Germany.[ pdf ] 
July 2002  Talk on the cosmic microwave background with focus on the different types of experiments.Held at the seminar of the Graduiertenkolleg Scientific Computing, University of Cologne,Germany.[ pdf ] 
February 2002  Talk on parameter estimation from recent type Ia supernova data in a nonstandard cosmological model. Originally designated for Dark Matter 2002.[ pdf ] 
January 2002  Talk on the estimation of cosmological parameters from the magnituderedshift relation by using type Ia supernova data. Held at the seminar of the Graduiertenkolleg Scientific Computing, University of Cologne, Germany. [ pdf ] 
September 2001  Talk on a new cosmological model in WeylCartan spacetime. Held at the Journees Relativistes, University College Dublin, Ireland.[ pdf ] 
June 2001  Talk on the cosmological standard model and on a cosmological solution in an alternative theory of gravity at the seminar of the Graduiertenkolleg Scientific Computing, University of Cologne, Germany [ pdf ] 
March 2001  Talk on a cosmological solution in WeylCartan spacetime at the annual meeting of the German Physical Society (DPG), University of Bonn, Germany. [ pdf ] 
November 2000  Invited lecture on an exact planefronted wave solution in metricaffine gravity at a Conference in honour of Heinz Dehnen's 65th and Dietrich Kramer's 60th birthday." Held at CINVESTAVIPN, Mexico City. 
September 2000  Talk on cosmological solutions in metricaffine gravity at the seminar of the Graduiertenkolleg Scientific Computing, University of Cologne, Germany. Partly based on an article on a cosmological model in WeylCartan spacetime. 