Machines are more expensive in poor countries, and the relation is pronounced. It is hard for a Solow (1956) type of model to explain the relation between machine prices and GDP given that in most countries equipment investment is under 10% of GDP. A stronger relation emerges in a Solow (1959)...

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...

This paper analyzes a decentralized process for the diffusion of knowledge. In equilibrium, the economy converges from an initial distribution of knowledge over agents to the steady-state distribution, which is unique. Because of the public good aspect of information, too little learning takes...

This paper explores a model of innovation and spatial co mpetition over time. A key implication of the paper is that firms' size is posit ively autocorrelated across time. The mechanism that generates this persistence works only in heterogenous product markets and is based on the idea that...