Julian Onions We hear a lot about dark matter in astronomy. Some people consider it a fudge. In this talk we go through the evidence for dark matter and the history of it, and answer the questions in the title. No particular prior knowledge is assumed. Julian Onions is a Post Doctorate researcher at Nottingham University. He works with computer simulations of large fractions of the universe to understand trends in galaxy formation and evolution.. All welcome - admission free . Tea & biscuits. Donations welcome. Image by Chil Vera from Pixabay