We study how endogenous innovation and technology diffusion interact to determine the shape of the productivity distribution and generate aggregate growth. We model firms that choose to innovate, adopt technology, or produce with their existing technology. Costly adoption creates a spread...

We formalize the Keynesian insight that aggregate demand driven by sentiments can generate output fluctuations under rational expectations. When production decisions must be made under imperfect information about demand, optimal decisions based on sentiments can generate stochastic...

This paper endogenizes the frequency of major discoveries and the extent of their refinement. Four axioms deliver a one-parameter family of beliefs that guide exploratory effort. Such effort trades off the prospect of major new discovery against the chance of successfully refining discoveries...

In a Bayesian model of learning, the more an agent uses a technology, the better he learns its parameters. This expertise is a form of human capital. Switching to a new technology temporarily reduces expertise: the bigger the leap, the bigger the loss. This may prevent the agent from climbing...