Mass Inflation

Mass inflation is the phenomenon in which perturbations grow without bound near the inner horizon of a charged or rotating black hole, causing the local mass function to diverge. First identified by Poisson and Israel in 1990, mass inflation arises because the inner Cauchy horizon acts as a magnifying lens for infalling radiation: waves that enter the black hole are blue-shifted infinitely as they approach the Cauchy horizon, creating a pile-up of energy density that overwhelms the background geometry.

The process is generic. Any real black hole formed by collapse will have perturbations — gravitational waves, electromagnetic radiation, or quantum fluctuations — and all such perturbations are amplified by the same geometric mechanism. Mass inflation transforms what the exact Kerr-Newman and Reissner-Nordström solutions depict as a traversable inner horizon into a curvature singularity, effectively converting the inner horizon into a genuine boundary.

This has decisive implications for the chronology protection conjecture and strong cosmic censorship, since mass inflation appears to enforce predictability by destroying the Cauchy horizon before observers can reach it. The divergence of the mass function may be a coordinate effect or a genuine physical singularity — the distinction depends on the still-unsolved problem of how quantum gravity regularizes classical divergences.