  In order to relate the probabilistic predictions of quantum theory uniquely
to measurement results, one has to conceive of an ensemble of identically
prepared copies of the quantum system under study. Since the universe is the
total domain of physical experience, it cannot be copied, not even in a thought
experiment. Therefore, a quantum state of the whole universe can never be made
accessible to empirical test. Hence the existence of such a state is only a
metaphysical idea. Despite prominent claims to the contrary, recent
developments in the quantum-interpretation debate do not invalidate this
conclusion.
