Testing the Equivalence Principle for Dark Matter Marc Kamionkowski, Robinson Professor of Theoretical Physics and Astrophysics, California Institute of Technology

According to an apocryphal story, Galileo dropped objects from the Leaning Tower to demonstrate that objects of different compositions fall the same way in a gravitational field, a notion we now call the equivalence principle. But what about dark matter? Does the dark matter that makes up most of our Galaxy fall the same way in a gravitational field? I will explain how astronomical observations can be used to answer this question.