Start the Week is at the Free Thinking Festival at Sage, Gateshead where Tom Sutcliffe explores the pace and rhythm of life - from the heart-stopping moments to the sleep of the innocent. His guests include Russell Foster whose work on circadian rhythms sheds light on the mechanisms of our body clocks and sleep. The crime writer Denise Mina is more interested in counting the bodies than counting sheep, as she revels in the psychological undercurrents in her latest thriller. The cardiac surgeon Stephen Westaby understands the delicate balance between life and death: he has saved hundreds of lives, holding each heart in his hand and feeling its beat. The mathematician Eugenia Cheng considers what it means when that beat goes on forever, with her study of the infinite. Producer: Katy Hickman.