On Start the Week Tom Sutcliffe talks to the American writer Jonathan Franzen about his latest novel, Purity. One of Franzen's characters compares the internet with the East German Republic and he satirises the utopian ideas of the apparatchik web-users. The head of the Oxford Internet Institute Helen Margetts counters with her research on the success and failure of political action via social media. The artist Tacita Dean laments the ubiquity of digital at the expense of film, and the financial journalist Gillian Tett roots out tunnel vision - both personal and business - in her new book on silos.