Back to the future: Gravity at sixty

This essay travels back from its origin to the future with gravity. The return to (what we would now call) gravity's non-parametric origin in Tinbergen (1962) takes a clue forward to improved non-parametric practice. In between, gravity became a structural parametric object widely used for policy projections and other counterfactuals. Non-parametric gravity described in Anderson (2023) leads to sufficient statistics for trade frictions, derived from the observable difference in welfare cost per unit in the observed and the observable as-if-frictionless equilibria. Relative resistance so defined is an origin for a renewed Tinbergen strategy of investigating trade friction determinants.