What does it mean to be free?  And what does it mean to live a personally authentic, honest life with ourselves and with others? These are the questions that Jean-Paul Sartre, Simone de Beauvoir and their existential friends wrestled with in the late 1940s and early 1950s. Sarah Bakewell makes the case that their late-night conversations are especially relevant today. She’s the author of “At the Existentialist Cafe: Freedom, Being, and Apricot Cocktails.”