White holes, black holes, andCPTin two dimensions

It is argued that a unitarity-violating but weakly $\mathrm{CPT}$ invariant superscattering matrix exists for leading-order large-$N$ dilaton gravity, if and only if one includes in the Hilbert space Planckian "thunderpop" excitations which create white holes. $\mathrm{CPT}$ apparently cannot be realized in a low-energy effective theory in which such states have been integrated out. Rules for computing leading-large-$N$ superscattering are described in terms of quantum field theory on a single multiply connected spacetime obtained by sewing the future (past) horizons of the original spacetime with the past (future) horizons of its $\mathrm{CPT}$ conjugate. Some difficulties which may arise in going beyond leading order in $\frac{1}{N}$ are briefly discussed.