Environmental decoherence is widely held to be the key to understanding the emergence of classicality in a quantum universe. However, in conjunction with traditional principles of interpretation, decoherence leaves unanswered a fundamental question, a version of the quantum measurement problem: Why should macroscopic objects have definite properties at all? I critically evaluate a variety of interpretive strategies intended to parlay the formal results of decoherence into the definiteness, or apparent definiteness, of familiar macroscopic properties. I argue that the crucial role of environmental decoherence in accounting for definite properties is effecting the dynamical decoupling of components of the global quantum state for which these properties are definite.
This role of decoherence is most evident in the context of the Everett interpretation, where considerations regarding branch dynamics lead naturally to the conclusion that dynamical autonomy (non-interference) of branches is a restriction on any division of the global quantum state into branches. Environmental decoherence results in the requisite dynamical autonomy for branches in which familiar macroscopic observables are definite, thus providing a natural and principled way to identify an interpretation basis.
The modal interpretation, with its property ascription rule based on the spectral decomposition of the reduced state, secures the right definite properties only in those cases in which it picks out properties that correspond almost exactly with the non-interfering components of the global quantum state. I argue that the non-interference of these components should be accorded interpretational significance in its own right; then the right properties can be specified without recourse to the distinctive property ascription rules of the modal interpretation.
Finally, I criticize attempts of decoherence theorists to account for definite properties by appeal to effects of decoherence such as approximate diagonality of the reduced state and preservation of correlations with respect to a set of privileged states. I argue that definiteness can be accounted for by looking not to these effects but to their cause, the dynamical autonomy of the environmentally-privileged components of the global quantum state. Precisely because they are dynamically autonomous, these states can be accorded physical significance in their own right.
|Advisor:||Ruetsche, Laura, Earman, John|
|School:||University of Pittsburgh|
|School Location:||United States -- Pennsylvania|
|Source:||DAI-A 72/05, Dissertation Abstracts International|
|Subjects:||Philosophy of Science, Quantum physics|
|Keywords:||Decoherence, Interpretations of quantum mechanics, Measurement problem, Quantum mechanics|
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