  With a choice of boundary conditions for solutions of the Schr\"odinger
equation, state vectors and density operators even for closed systems evolve
asymmetrically in time. For open systems, standard quantum mechanics
consequently predicts irreversibility and signatures of the extrinsic arrow of
time. The result is a new framework for the treatment of decoherence, not based
on a reduced dynamics or a master equation. As an application, using a general
model we quantitatively match previously puzzling experimental results and can
conclude that they are the measurable consequence of the indistinguishability
of separate, uncontrolled interactions between systems and their environment.
