From my limited understanding of QM, it would appear that their assertion, that all "mixed" states are really part of a "pure" state, is just a restatement of t

From my limited understanding of QM, it would appear that their assertion, that all "mixed" states are really part of a "pure" state, is just a restatement of the Many Worlds hypothesis. In the MW hypothesis, reality is described by the wavefunction of the whole universe, which is a single "pure" vector in Hilbert space whose operators are observables on the whole universe.