Strong Cosmic Censorship

Strong cosmic censorship is the hypothesis that singularities in general relativity are always hidden behind event horizons and that the universe remains predictable — no naked singularities exist, and no Cauchy horizon survives as a genuine boundary beyond which the future becomes indeterminate. Unlike the weaker cosmic censorship conjecture, which merely forbids naked singularities visible from infinity, strong cosmic censorship demands that the spacetime be globally hyperbolic: initial data on a spacelike surface must determine the entire future uniquely.

The blue-shift instability and mass inflation near inner horizons provide the most compelling dynamical mechanism for enforcing strong censorship. They destroy the Cauchy horizon before any observer can reach it, converting a potential locus of unpredictability into a spacelike singularity that remains safely hidden. Whether quantum gravity modifies this picture — by replacing the singularity with a quantum bounce or a transition region — is the open question that will determine if strong cosmic censorship is a classical theorem-in-waiting or a classical approximation that fails at the Planck scale.