  A goal of most interpretations of quantum mechanics is to avoid the apparent
intrusion of the observer into the measurement process. Such intrusion is
usually seen to arise because observation somehow selects a single actuality
from among the many possibilities represented by the wavefunction. The issue is
typically treated in terms of the mathematical formulation of the quantum
theory. We attempt to address a different manifestation of the quantum
measurement problem in a theory-neutral manner. With a version of the two-slit
experiment, we demonstrate that an enigma arises directly from the results of
experiments. Assuming that no observable physical phenomena exist beyond those
predicted by the theory, we argue that no interpretation of the quantum theory
can avoid a measurement problem involving the observer.
