Is the universe a quantum system?

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 th e total domain of physical experience, it cannot be copied, not even in a t hought experiment. Therefore, a quantum state of the whole universe can nev er be made accessible to empirical test. Hence the existence of such a stat e is only a metaphysical idea. Despite prominent claims to the contrary, re cent developments in the quantum-interpretation debate do not invalidate th is conclusion.