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Measurement and the Illusion of Quantum Collapse

D. Ring

Published Feb 19, 2024• 0 citations
Publisher

Abstract

Models of quantum measurements are presented, including observers subject to the laws of quantum mechanics. Observers perform multiple measurements in an attempt to disprove the collapse hypothesis. It is shown that under reasonable assumptions the effort cannot succeed. Under a unitary evolution the end state is a correlation between the result of the first measurement and the result(s) of the others, consistent with the observer's collapse hypothesis. The observer may conclude that the laws of nature include a non-unitary collapse mechanism, even if one does not actually exist. Discard of information is the crucial factor which distinguishes entanglement from measurement.

DOI
10.20944/preprints202402.0959.v1

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Models of quantum measurements are presented, including observers subject to the laws of quantum mechanics. Observers perform multiple measurements in an attempt to disprove the collapse hypothesis. It is shown that under reasonable assumptions the effort cannot succeed. Under a unitary evolution the end state is a correlation between the result of the first measurement and the result(s) of the others, consistent with the observer's collapse hypothesis. The observer may conclude that the laws of nature include a non-unitary collapse mechanism, even if one does not actually exist. Discard of information is the crucial factor which distinguishes entanglement from measurement.
Models of quantum measurements are presented, including observers subject to the laws of quantum mechanics. Observers perform multiple measurements in an attempt to disprove the collapse hypothesis. It is shown that under reasonable assumptions the effort cannot succeed. Under a unitary evolution the end state is a correlation between the result of the first measurement and the result(s) of the others, consistent with the observer's collapse hypothesis. The observer may conclude that the laws of nature include a non-unitary collapse mechanism, even if one does not actually exist. Discard of information is the crucial factor which distinguishes entanglement from measurement.
This paper proposes an experiment designed to distinguish between competing interpretations of quantum mechanics: those that involve wave function collapse and those that assume purely unitary evolution. The experiment tests whether an observer can measure a system without collapsing its wave function. To this end, we introduce the concept of an unconscious observer, defined by two criteria: (1) It measures a quantum system and sets the state of another system based on the result. (2) It allows an external experimentalist to infer the measurement outcome by examining the observer's state. The more distinguishable the observer's resulting states, the more it resembles a conventional measurement apparatus. Using weak measurements, the experimentalist probes these states, thereby testing the second criterion. The interference patterns observed in this setup reveal whether collapse has occurred, allowing experimental discrimination between collapse-based and unitary interpretations.
The measurement postulate of quantum theory stands in conflict with the laws of thermodynamics and has evoked debate regarding what actually constitutes a measurement. With the help of modern quantum statistical mechanics, we take the first step in formalizing the hypothesis that quantum measurements are driven by the natural tendency of closed systems to maximize entropy, a notion that we call the measurement-equilibration hypothesis. In this paradigm, we investigate how classical measurement outcomes can emerge within a purely unitary framework, and find that (1) the interactions used in standard measurement models fail to spontaneously encode information classically and (2) while ideal projective measurements are impossible, one can (for a given form of Hamiltonian) approximate them exponentially well as more physical systems are collected together into an “observer” system. We thus lay the groundwork for self-contained models of quantum measurement, proposing improvements to our simple scheme.
The quantum measurement problem still finds no consensus. Nonlocal interferometry provides an unprecedented experimental probe by entangling two photons in the ``measurement state'' (MS). The experiments show that each photon measures the other; the resulting entanglement decoheres both photons; decoherence collapses both photons to unpredictable but definite outcomes; and the two-photon MS continues evolving coherently. Thus, when a two-part system is in the MS, the outcomes actually observed at both subsystems are definite. Although standard quantum physics postulates definite outcomes, two-photon interferometry verifies them to be not only consistent with, but also actually a prediction of, the other principles. Nonlocality is the key to understanding this. As a consequence of nonlocality, the states we actually observe are the local states. These actually observed local states collapse, whereas the global MS, which can be ``observed'' only after the fact by collecting coincidence data from both subsystems, continues its unitary evolution. This conclusion implies a refined understanding of the eigenstate principle: Following a measurement, the actually observed local state instantly jumps into the observed eigenstate. We also discuss and rebut objections to this.
The measurement problem — the question of why quantum superpositions appear to collapse to definite outcomes upon measurement — remains one of the most consequential unresolved questions in the foundations of physics. Despite the extraordinary empirical success of quantum mechanics, the field has for decades operated under an unofficial norm of interpretive silence, a posture Sean Carroll and others have identified as both intellectually dishonest and scientifically costly. This paper argues that the experimental evidence, properly understood through the framework of quantum entanglement and decoherence, provides strong grounds for rejecting the hypothesis that consciousness plays a causal role in wavefunction collapse. Three tiers of experimental evidence are examined: the double slit experiment with which-path detection, Bell inequality tests confirming non-local entanglement, and the LIGO gravitational wave detections demonstrating macroscopic quantum coherence at cosmological scales without any role for conscious observation. The paper concludes that the consciousness hypothesis is not supported by experimental physics and that Carroll's call for serious investment in foundational research is scientifically justified and philosophically urgent.
The entangled “measurement state” (MS), predicted by von Neumann to arise during quantum measurement, seems to display paradoxical properties such as multiple macroscopic outcomes. But analysis of interferometry experiments using entangled photon pairs shows that entangled states differ surprisingly from simple superposition states. Based on standard quantum theory, this paper shows that the MS (i) does not represent multiple detector readings but instead represents nonparadoxical multiple statistical correlations between system states and detector readings, (ii) implies that exactly one outcome actually occurs, and (iii) implies that when one outcome occurs, the other possible outcomes simultaneously collapse nonlocally. Point (iii) resolves an issue first raised in 1927 by Einstein who demonstrated that quantum theory requires instantaneous state collapse. This conundrum’s resolution requires nonlocal correlations, which from today’s perspective suggests the MS should be an entangled state. Thus, contrary to previous presumed proofs of the measurement problem’s insolubility, we find the MS to be the collapsed state and just what we expect upon measurement.