  Experimentally observed violations of Bell inequalities rule out local
realistic theories. Consequently, the quantum state vector becomes a strong
candidate for providing an objective picture of reality. However, such an
ontological view of quantum theory faces difficulties when spacelike
measurements on entangled states have to be described, because time ordering of
spacelike events can change under Lorentz-Poincar\'e transformations. In the
present paper it is shown that a necessary condition for consistency is to
require state vector reduction on the backward light-cone. A fresh approach to
the quantum measurement problem appears feasible within such a framework.
