Grimmer, Daniel
(2022)
The Pragmatic QFT Measurement Problem and the need for a Heisenberg-like Cut in QFT.
[Preprint]
Abstract
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 Problem. We can identify two kinds of worries: 1) pragmatic: it's unclear how to model our experiments to extract theoretical predictions, and 2) realist: there is no realist narrative for the experiment underlying these theoretical predictions. I will argue that while both deserve attention, the pragmatic worries have worse consequences if left unanswered. Moreover, upon reflection, a satisfactory prediction of many of quantum theory's key experimental successes unavoidably involves modeling quantum fields at some point. Without a satisfactory pragmatic theory-to-experiment link for QFT, we are at risk of losing any right to claim evidential support for large parts of quantum theory. This is the \textit{Pragmatic QFT Measurement Problem}.
But, what makes formalizing measurements in QFT so hard? As I will discuss, attempts to naively transplant projective measurements into QFT violate core tenets of relativity. Thus we need a new (or at least refined) measurement theory for QFT. However, as I will argue, aiming too directly at a new measurement theory is an incautious way to proceed and is apt to lead us astray. Instead, we ought to first review how our non-relativistic quantum measurement theory is rooted in notions of measurement chains and Heisenberg cuts. Next, we ought to generalize these notions and transplant them into QFT. My analysis suggests the need for a pragmatic \textit{QFT-cut} analogous to the Heisenberg cut. Finally, we can then see what measurement theory (if any) we are led to for QFT. As I will discuss, the Unruh-DeWitt detector model is uniquely positioned to give us a wide-scoping physically-meaningful measurement theory for QFT.
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The Pragmatic QFT Measurement Problem and the need for a Heisenberg-like Cut in QFT. (deposited 02 Jun 2022 15:37)
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