We know this because general relativity is a classical field theory which predicts that under certain conditions, infinities will occur...called singularities.

All known singularities in the theory seem to be hidden behind event horizons. At these locations, space-time curvature defined by the magnitude of the so-called Riemann Tensor, goes to infinity as the radius of the system goes to zero. It is expected that a make-over of general relativity by a fully quantum mechanical field theory (Superstrings, M-Theory, etc) will remove these singularities and replace them by some as yet undefined quantum condition, such as the finite graininess of space-time itself at the Planck Scale.

Copyright 1997 Dr. Sten Odenwald