Edd works in astronomy at the University of Portsmouth, trying to handle the large amounts of data from some of the current and upcoming surveys of the sky. He's worked with surveys such as the Sloan Digital Sky Survey (SDSS), and on the 'citizen science' project Galaxy Zoo which lead to the discovery of 'Hanny's Voorwerp'. As someone in the field of cosmology, he's in the somewhat unusual situation of often having to tell people that most of the universe is actually invisible and intangible and that it's perfectly rational to believe that.  Having spent too much time worrying about how to turn data into answers to questions, he talks about the mathematics behind thinking skeptically (but not so many equations that you can't follow him after a pint or two). What should we mean when we say we believe something? How do you know when you have enough evidence for your beliefs, and when should you change your mind when faced with facts that don't fit your preconceptions? And what does this all mean when we're faced with the task of assessing whether that claimed psychic really can do what they say?