Over the 13 years of doing this show one of the things that we, and indeed all of the field of Astrophysics, has been trying to get our collective head around is the idea of Dark Matter and Dark Energy. To the layperson, these ideas can seem like rather convenient inventions thought up merely to paper over the cracks in our current models. But let’s be honest, most of us don’t really know enough about physics to make such bold accusations. This week's guest however does, and not only does he think that there is no such thing as Dark Matter, he also says our fundamental model of gravitation is wrong. Pavel Kroupa is a Professor of astrophysics at the University of Bonn and Head of the Stellar Populations and Dynamics research group. He joins Jonathan to discuss.

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