The Measurement Process in Local Quantum Theory and the EPR Paradox

TL;DR

This paper proposes a qualitative model of the quantum measurement process considering finite interaction time, apparatus size, and particle number, aiming to reconcile measurement with locality principles in quantum field theory.

Contribution

It introduces a new conceptual framework for quantum measurement that incorporates finite interaction duration, apparatus size, and particle number, challenging the traditional instantaneous collapse model.

Findings

Measurement arises only in the limit of infinite apparatus size and zero interaction time.

The local measurement scheme aligns with the Principle of Locality.

Reformulates EPR paradox using local observables to resolve non-locality issues.

Abstract

We describe in a qualitative way a possible picture of the Measurement Process in Quantum Mechanics, which takes into account: 1. the finite and non zero time duration T of the interaction between the observed system and the microscopic part of the measurement apparatus; 2. the finite space size R of that apparatus; 3. the fact that the macroscopic part of the measurement apparatus, having the role of amplifying the effect of that interaction to a macroscopic scale, is composed by a very large but finite number N of particles. The conventional picture of the measurement, as an instantaneous action turning a pure state into a mixture, arises only in the limit in which N and R tend to infinity, and T tends to 0. We sketch here a proposed scheme, which still ought to be made mathematically precise in order to analyse its implications and to test it in specific models, where we argue that in Quantum Field Theory this picture should apply to the unique time evolution expressing the dynamics of a given theory, and should comply with the Principle of Locality. We comment on the Einstein Podolski Rosen thought experiment (partly modifying the discussion on this point in an earlier version of this note), reformulated here only in terms of local observables (rather than global ones, as one particle or polarisation observables). The local picture of the measurement process helps to make it clear that there is no conflict with the Principle of Locality.