Kretschmann Scalar
\[K = R_{abcd}R^{abcd} = \frac{48G^2M^2}{c^4r^6}\]
True Physical Singularity
Unlike the horizon, the singularity at r=0 is a true physical singularity. The Kretschmann scalar K, which measures spacetime curvature, diverges as r approaches zero. This indicates infinite tidal forces and the breakdown of General Relativity.
Limits of General Relativity
At the singularity, classical General Relativity predicts its own failure. A theory of Quantum Gravity is required to describe physics at this scale, but such a theory does not yet exist.