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The Pragmatic QFT Measurement Problem and the need for a Heisenberg-like Cut in QFT

Grimmer, Daniel (2023) The Pragmatic QFT Measurement Problem and the need for a Heisenberg-like Cut in QFT. [Preprint]

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Despite quantum theory's remarkable success at predicting the statistical results of experiments, many philosophers worry that it nonetheless lacks some crucial connection between theory and experiment. Such worries constitute the Quantum Measurement Problems. One can broadly identify two kinds of worries: 1) pragmatic: it is unclear how to model our measurement processes in order to extract experimental predictions, and 2) realist: we lack a satisfying ontological account of measurement processes. While both issues deserve attention, the pragmatic worries have worse consequences if left unanswered: If our pragmatic theory-to-experiment linkage is unsatisfactory, then quantum theory is at risk of losing both its evidential support and its physical salience. Avoiding these risks is at the core of what I will call the Pragmatic Measurement Problem.

Fortunately, the pragmatic measurement problem is not too difficult to solve. For non-relativistic quantum theory, the story goes roughly as follows: One can model each of quantum theory's key experimental successes on a case-by-case basis by using a measurement chain. Somewhere along this measurement chain it is pragmatically necessary to cross the quantum-classical divide by invoking a pragmatic Heisenberg cut. Past this case-by-case measurement framework, one can then strive for a wide-scoping measurement theory capable of modeling all (or nearly all) possible measurement processes, e.g. our usual projective measurement theory. As a bonus, proceeding this way also gives us a physically meaningful characterization of the theory's observables.

But how does this story have to change when we move into the context of quantum field theory (QFT)? It is well known that in QFT almost all projective measurements violate causality, allowing for faster-than-light signaling; These are Sorkin's impossible measurements. It has been argued in the physics literature that because of this we need a new (or at least refined) measurement theory for QFT. I will argue, however, that aside from some technical complications, moving into a QFT context changes essentially nothing regarding how we can and should model quantum measurements. The story ought to proceed exactly as before: We ought to first use measurement chains to build up a case-by-case measurement framework for QFT. This will require us to cross the QFT-non-QFT divide at some point along the measurement chain. From here we can then strive for both a new wide-scoping measurement theory for QFT and a new characterization of its observables. This paper ends by briefly reviewing the state of the art in the physics literature regarding the modeling of measurement processes involving quantum fields.

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Item Type: Preprint
Grimmer, Danieldaniel.j.grimmer@gmail.com0000-0002-8449-3775
Additional Information: Video Abstract:
Keywords: quantum measurement problem; quantum field theory; observables; observables of QFT; Heisenberg cut; measurement chain;
Subjects: Specific Sciences > Physics > Quantum Field Theory
Specific Sciences > Physics > Quantum Mechanics
Depositing User: Dr. Daniel Grimmer
Date Deposited: 11 Mar 2023 15:31
Last Modified: 11 Mar 2023 15:31
Item ID: 21865
Subjects: Specific Sciences > Physics > Quantum Field Theory
Specific Sciences > Physics > Quantum Mechanics
Date: 2023

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