In 1971, Phelps moved to the Economics Department at Columbia University, where Nobel prize winners William Vickrey and James J. Heckman were studying. Nobel Prize winner Robert Mundell joined three years later, as well as Phoebus Dhrymes, Guillermo Calvo and John B. Taylor. Professor Phelps published research on the inflation tax and the effects of fiscal policy on inflation. In 1972, Phelps published a book about his new theory. The book had many ideas about the effects of being unemployed for a long time and made him more popular.