**Title**: The Physics of Black Hole Interiors

**Abstract**:

It has been known since the work of Barrabes, Israel, and Poisson in 1990 that the inner horizons of rotating black holes are subject to the mass inflation instability, yet there has been astonishingly little investigation of the instability. The instability acts like a gravity-powered particle accelerator of extraordinary power. If quantum gravity did not intervene, the accelerator would accelerate ingoing and outgoing streams through each other to collision energies far above the Planck scale. I will report recent progress on the inflationary instability in rotating black holes. I suggest that the problem is ripe for numerical investigation.