"Human capital-based theories of cities suggest that large, economically diverse urban agglomerations increase worker productivity by increasing the rate at which individuals acquire skills. One largely unexplored implication of this theory is that workers in big cities should see faster growth...

"In this paper, we construct a simple model based on heterogeneity in workers' productivity and homogeneity in their working schedules. This simple model can generate unemployment, even if wages adjust instantaneously, firms are perfectly competitive, and firms can perfectly observe workers'...