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Morbert

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Morbert said:Decoherent histories has been around for a good few decades at this stage, with one motivation for its development being the description of closed systems, and measurements as processes therein.

https://www.webofstories.com/play/murray.gell-mann/163

https://iopscience.iop.org/article/10.1088/1742-6596/2533/1/012011/pdf

https://arxiv.org/abs/1704.08725

It gives a clear account of what it means for a measurement to occur in a closed system. It might even recover the ensemble interpretation insofar as we could conceptualize an infinite ensemble of histories of the universe and associate measurement with correlations over the ensemble.

A. Neumaier said:No. It only gives an account of events ''that we can talk about at the breakfast table'' (according to the above paper) - not of dynamical processes that would qualify as measurement processes.

In particular, their discussion assumes measurement results that fall from heaven, given by a POM or POVMin addition to the untary dynamics of the system, rather than taking the state of the universe andderiving from itthe distribution of the values read from a macroscopic detector that is part of the dynamics.

Thus everything is empty talk embellishing Born's rule.

Given some quantum theory of an isolated system, as well as a quantum of state of that isolated system, decoherent/consistent histories will ascribe meaning to event probabilities of the isolated system, without needing to couple the system to some ancilla. This is more or less the ambition of decoherent histories as an interpretation. It does not privilege any measure as more correct than any other, and we choose whatever measure is suitable for computing the probabilities for events we are interested in when we carry out a measurement.

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