The issue with the initial state in quantum mechanics

Abstract

In the conventional formulation of quantum mechanics, the initial description is given only for the physical system under study. It factors out the state for the experimenter. We argue that such description is incomplete and can lead to statements which can in theory be meaningless. We propose that within a complete description, the initial state must include the state of the experimenter. With such formulation quantum mechanics provides joint probabilities for conjointly observed events, rather than a probability conditional on some initial state for the system under study. This feature is desirable, as with quantum mechanics, statements on what happened in the past may have no meaning in the present.