* Speaker : Prof. Sascha Trippe (Seoul National University)
* Abstract : The 'missing mass problem' has puzzled astronomers for decades. Assuming the validity of Newtonian / Einsteinian gravity on astronomical scales, the universe must contain about ten times more mass than can be observed directly - the cosmos seems to be filled with 'dark matter'. However, all searches for this 'invisible' matter have been fruitless so far. This has led to increasing attention for modified theories of gravity as a possible alternative explanation. I am going to review the key ideas, observational constraints, and the impact of the recent direct detection of gravitational waves for our understanding of gravity on astronomical scales.