Indistinguishability and the external correlation of mixtures

Experimental evidence, the heuristics of indistinguishability, and its logical inconsistency with quantum formalism all argue against the existence of a quantum mixture uncorrelated with the exterior, hence argue for the postulate “The state of a system uncorrelated with its exterior is pure.” It is shown that this is equivalent with “The state of a system describable in terms of indistinguishable pure states is pure,” and with “The state of the universe is pure,” and yields a quantitative expression of the traditional relation of welcher Weg information to partial coherence. Thus, all mixtures are “improper,” the trace-reduction of a composite system’s pure state.