  This essay contends that in quantum gravity, some spatial regions do not
admit a unitary Hilbert space. Because the gravitational path integral
spontaneously breaks CPT symmetry, "states" with negative probability can be
identified on either side of trapped surfaces. I argue that these negative norm
states are tolerable, by analogy to quantum mechanics. This viewpoint suggests
a resolution of the firewall paradox, similar to black hole complementarity.
Implications for cosmology are briefly discussed.
