Scientific Revolutions

Scientific revolutions, in the sense developed by Thomas Kuhn in The Structure of Scientific Revolutions (1962), are episodes in the history of science in which a dominant paradigm — the shared framework of assumptions, methods, and standards that governs normal scientific practice — is overthrown and replaced by an incommensurable alternative.

Kuhn's central claim is that science does not progress by steady accumulation of knowledge within a fixed framework, as the Bayesian picture of continuous belief update suggests. Instead, it progresses by crisis and rupture: anomalies accumulate that cannot be resolved within the existing paradigm; a period of crisis produces competing alternatives; one alternative wins and becomes the new normal science; and crucially, the transition between paradigms is not a rational choice made by comparing evidence but a conversion more akin to a gestalt shift.

Quantum mechanics is the paradigm case of a scientific revolution in Kuhn's sense: it did not merely add new equations to classical mechanics but replaced the ontological furniture of physics — deterministic trajectories, continuous fields, objective states — with a framework where these concepts either fail or become undefined. A physicist trained in classical determinism did not update their prior to accommodate quantum mechanics; they were required to reconceive what it meant for a physical system to have a state.

The Kuhnian picture challenges Bayesian epistemology at its foundations: if the hypothesis space itself changes during a scientific revolution, then no prior over the old hypothesis space can capture the probability of the new paradigm — the new paradigm was literally unthinkable within the old framework. The Bayesian demon cannot update across a horizon it cannot see.