Carlo Rovelli is an Italian theoretical physicist. In his new book, The Order of Time, Rovelli asks "Why do we remember the past and not the future…What ties time to our nature as persons, to our subjectivity?" Rovelli is the head of the Quantum Gravity group at the Centre de Physique Théorique of Aix-Marseille University and has devoted his life's work to understanding what time might truly be. Author and philosopher, Jim Holt spoke with Rovelli about the past, future, and why there isn't exactly a "now."