policy, and optimal population growth. In the following years, an element in Phelps's foundations came under heavy criticism with the introduction of John Muth's rational expectations, which was popularized by future Nobel prize winner Robert Lucas, Jr. Phelps, with Calvo and John Taylor, started a program to rebuild Keynesian economics with rational expectations by employing sticky wages and prices. They did so by explicitly incorporating in models the fact that wage contracts are set in advance for multiple periods, an idea originating from Phelps's 1968 paper. This research lead to a paper published with Taylor in 1977, proving that staggered wage setting gives monetary policy a role in stabilizing economic fluctuations. The use of staggered wage and price setting, further developed by Calvo in a 1983 paper, became a cornerstone of New Keynesian economics. During the 1970s, Phelps and Calvo also collaborated on research on optimal contracts under asymmetric information. Phelps spent 1969–70 at the Center for Advanced Study in Behavioral Science at Stanford University. Discussions with fellow Nobel prize winners Amartya Sen and Kenneth Arrow and especially the influence of the philosophy of John Rawls, whom he met during the year at the Center, led Phelps to undertake some research outside macroeconomics. As a result, in 1972, he published seminal research in the new field that he named statistical discrimination. He also published research on economic justice, applying ideas from Rawls's A Theory of Justice. In 1971, Phelps moved to the Economics Department at Columbia University, which also included future Nobel prize winners William Vickrey and James J. Heckman (future laureate Robert Mundell joined three years later), as well as Phoebus Dhrymes, Guillermo Calvo and John B. Taylor. There, he published research on the inflation tax and the impact of fiscal policy on optimal inflation. In 1972, Phelps published a new book which focused on the derivation of policy implications of his new theory. The book further popularized his "expectations-augmented Phillips curve" and introduced the concept of hysteresis with regard to unemployment (prolonged unemployment is partially irreversible as workers lose skill and become demoralized). In the late 1970s, Phelps and one of his former students, Roman Frydman, conducted some research on the implications of assuming rational expectations, at first independently and then in collaboration. Their results suggested that rational expectations are not the correct way to model agents' expectations. They organized a conference on the issue in 1981 and