Original sentence: Before the measurement has started the observer states are identical, after the measurement is complete the observer states are orthonormal.In Dirac notation a measurement is complete when:.In such circumstances the universal wavefunction is still available to give a complete description of reality.MWI response: the decoherence or "splitting" or "branching" is complete when the measurement is complete.Since the role of the observer and measurement plays no special role in MWI there is no need for a precise definition of what an observer is or a measurement is.The flip side of quantum suicide is quantum immortality.Thus a measurement defines the branching process: the branching is as well- or ill- defined as the measurement is.Thus branching is complete when the measurement is complete.where O[i] represents the observer having detected the object system in the ith state
Edited sentence: In the original Everett formulation this vagueness was about measurement, where there was no given criterion to explain when the measurement happens, it depended on unspecified way to split system into two subsystems