Measurements without probabilities in the final state proposal.

The black hole final state proposal reconciles the Mailing vacuum with the unitarity of the Hawking radiation, but only for some experiments. We study experiments that first verify the exterior, then the interior purification of the same Hawking particle. (This is the same protocol that renders the firewall paradox operationally meaningful in standard quantum mechanics.) We show that the decoherence functional fails to be diagonal, even upon inclusion of external''pointer" systems. Hence, probabilitiesforoutcomesofthese measurements are not defined. We conclude that the final state proposal does not offer a consistent alternative to the firewall hypothesis. [ABSTRACT FROM AUTHOR]