Decoherence and its role in the modern measurement problem

Abstract

Decoherence is widely felt to have something to do with the quantum measurement problem, but getting clear on just what is made difficult by the fact that the 'measurement problem', as traditionally presented in foundational and philosophical discussions, has become somewhat disconnected from the conceptual problems posed by real physics. This, in turn, is because quantum mechanics as discussed in textbooks and in foundational discussions has become somewhat removed from scientific practice, especially where the analysis of measurement is concerned. This paper has two goals: firstly ( § §1-2), to present an account of how quantum measurements are actually dealt with in modern physics (hint: it does not involve a collapse of the wave function) and to state the measurement problem from the perspective of that account; and secondly ( § §3-4), to clarify what role decoherence plays in modern measurement theory and what effect it has on the various strategies that have been proposed to solve the measurement problem.

Emergence of a classical Universe from quantum gravity and cosmology

“…But, as David Wallace has emphasized [15], 'It does not, however, in any way blunt the metaphysically shocking aspect of Everett's proposal: no one quasi-classical branch is singled out as real; all are equally part of the underlying quantum reality'.…”

Yes, More Decoherence: A Reply to Critics

“…A slightly fuller version of the arguments sketched here can be found in Wallace (2012a), "Decoherence and its role in the modern measurement problem". The takeaway from these arguments and my own are that one need not attribute ontological meaning to the Born rule as long as one avoids assuming that appearances depict reality, that measurement outcomes are all and only what they seem.…”

“…My aim was to disentangle this overlap, and thereby restrict the amount of philosophical baggage being needlessly hauled into relativistic discussions of quantum mechanics. A similar project -philosophical housekeeping regarding the measurement problem -is carried out in Wallace (2012a). Although Wallace's ultimate aim is to defend the Everett interpretation, he too sees the necessity of separating the projection postulate out of the "standard formalism" and recasting the measurement problem to be in closer alignment with experimental practices.…”

Decoherence

“…That decoherence is instrumental to the foundational resolution of the quantum measurement problem is the starting point for Wallace [9], a philosopher of physics, who clarifies the exact role decoherence may play in attempts to give a dynamical analysis to the measurement process, and in so doing reformulates the measurement problem to better fit contemporary scientific practice. He then analyses the role decoherence plays in each of the possible solutions (and dissolutions) of the problem, either as constraint on those approaches that aim to modify quantum theory or as a consistency requirement between the underlying quantum dynamics and the apparent classical behaviour.…”