  The definition of matter states on spacelike hypersurfaces of a 1+1
dimensional black hole spacetime is considered. Because of small quantum
fluctuations in the mass of the black hole, the usual approximation of treating
the gravitational field as a classical background on which matter is quantized,
breaks down near the black hole horizon. On any hypersurface that captures both
infalling matter near the horizon and Hawking radiation, a semiclassical
calculation is inconsistent. An estimate of the size of correlations between
the matter and gravity states shows that they are so strong that a fluctuation
in the black hole mass of order exp[-M/M_{Planck}] produces a macroscopic
change in the matter state. (Talk given at the 7th Marcel Grossmann Meeting on
work in collaboration with E. Keski-Vakkuri, G. Lifschytz and S. Mathur.)
