A new class of problems in the calculus of variations.

Summary We revisit the neo-classical model of optimal growth by introducing an additional term, due to Chichilnisky, which embodies society's concern for the long-term welfare of future generations. We show that the additional term causes time inconsistency, so there is no such thing as an optimal solution. However, we introduce a notion of equilibrium solution and we prove that there is a continuum of such solutions.