# Weekly Papers on Quantum Foundations (30)

The Real Meaning of Quantum Mechanics. (arXiv:2107.10666v1 [quant-ph])

We suggest a contextual realist interpretation of relational quantum mechanics. The principal point is a correct understanding of the concept of reality and taking into account the categorical distinction between the ideal and the real. Within our interpretation, consciousness of the observer does not play any metaphysical role. The proposed approach can also be understood as a return to the Copenhagen interpretation of quantum mechanics, corrected within the framework of contextual realism. The contextual realism allows one to get rid of the metaphysical problems encountered by various interpretations of quantum mechanics, including the relational one.

Decoherence-Free Entropic Gravity: Model and Experimental Tests. (arXiv:2012.10626v2 [quant-ph] UPDATED)

Erik Verlinde’s theory of entropic gravity [arXiv:1001.0785], postulating that gravity is not a fundamental force but rather emerges thermodynamically, has garnered much attention as a possible resolution to the quantum gravity problem. Some have ruled this theory out on grounds that entropic forces are by nature noisy and entropic gravity would therefore display far more decoherence than is observed in ultra-cold neutron experiments. We address this criticism by modeling linear gravity acting on small objects as an open quantum system. In the strong coupling limit, when the model’s unitless free parameter $\sigma$ goes to infinity, the entropic master equation recovers conservative gravity. We show that the proposed master equation is fully compatible with the \textit{q}\textsc{Bounce} experiment for ultra-cold neutrons as long as $\sigma\gtrsim 250$ at $90\%$ confidence. Furthermore, the entropic master equation predicts energy increase and decoherence on long time scales and for large masses, phenomena which tabletop experiments could test. In addition, comparing entropic gravity’s energy increase to that of the Di\'{o}si-Penrose model for gravity induced decoherence indicates that the two theories are incompatible. These findings support the theory of entropic gravity, motivating future experimental and theoretical research.

Do gravitational waves confirm Hawking’s area law?. (arXiv:2107.10680v1 [physics.hist-ph])

Authors: Galina Weinstein

Recently an experiment has been performed for the purpose of “testing the area law with GW150914”. As the experimenters put it, the experiment presents “observational confirmation” of Hawking’s area law based on the GW150914 data. It is the purpose of this paper to philosophically examine the test of the area law and to show that the area law is not confirmable yet is falsifiable. Accordingly, the GW150914 data do not confirm Hawking’s area law. What has been tested with positive results was the hypothesis A3 > A1 + A2, where A3 = GW150914 remnant and A1 + A2 = GW150914 merger. But this single instance does not provide observational confirmation of Hawking’s area law.

Bell Nonlocality and the Reality of Quantum Wavefunction. (arXiv:2005.08577v4 [quant-ph] UPDATED)

Status of quantum wavefunction is one of the most debated issues in quantum foundations — whether it corresponds directly to the reality or just represents knowledge or information about some aspect of reality. In this letter we propose a {\it $\psi$-ontology} theorem that excludes a class of ontological explanations where quantum wavefunction is treated as mere information. Our result, unlike the acclaimed Pusey-Barrett-Rudolph’s theorem, does not presume the absence of holistic ontological properties for product quantum preparations. At the core of our derivation we utilize the seminal no-go result by John S. Bell that rules out any local realistic world view for quantum theory. We show that the observed phenomenon of quantum nonlocality cannot be incorporated in a class of $\psi$-epistemic models. Using the well known Clauser-Horne-Shimony-Holt inequality we obtain a threshold bound on the degree of epistemicity above which the ontological models are not compatible with quantum statistics.

Unifying theory of quantum state estimation using past and future information

Publication date: Available online 20 July 2021

Source: Physics Reports

Author(s): Areeya Chantasri, Ivonne Guevara, Kiarn T. Laverick, Howard M. Wiseman

Quantum state estimation for continuously monitored dynamical systems involves assigning a quantum state to an individual system at some time, conditioned on the results of continuous observations. The quality of the estimation depends on how much observed information is used and on how optimality is defined for the estimate. In this work, we consider problems of quantum state estimation where some of the measurement records are not available, but where the available records come from both before (past) and after (future) the estimation time, enabling better estimates than is possible using the past information alone. Past-future information for quantum systems has been used in various ways in the literature, in particular, the quantum state smoothing, the most-likely path, and the two-state vector and related formalisms. To unify these seemingly unrelated approaches, we propose a framework for partially observed quantum systems with continuous monitoring, wherein the first two existing formalisms can be accommodated, with some generalization. The unifying framework is based on state estimation with expected cost minimization, where the cost can be defined either in the space of the unknown record or in the space of the unknown true state. Moreover, we connect all three existing approaches conceptually by defining five new cost functions, and thus new types of estimators, which bridge the gaps between them. We illustrate the applicability of our method by calculating all seven estimators we consider for the example of a driven two-level system dissipatively coupled to bosonic baths. Our theory also allows connections to classical state estimation, which create further conceptual links between our quantum state estimators.

Hartle-Hawking state in the real-time formalism. (arXiv:2107.10271v1 [gr-qc])

Authors: Atsushi HiguchiWilliam C. C. Lima

We study self-interacting massive scalar field theory in static spacetimes with a bifurcate Killing horizon and a wedge reflection. In this theory the Hartle-Hawking state is defined to have the $N$-point correlation functions obtained by analytically continuing those in the Euclidean theory, whereas the double KMS state is the pure state invariant under the Killing flow and the wedge reflection which is regular on the bifurcate Killing horizon and reduces to the thermal state at the Hawking temperature in each of the two static regions. We demonstrate in the Schwinger-Keldysh operator formalism of perturbation theory the equivalence between the Hartle-Hawking state and the double KMS state with the Hawking temperature, which was shown before by Jacobson in the path-integral framework.

Noether’s first theorem and the energy-momentum tensor ambiguity problem

Baker, Mark Robert and Linnemann, Niels and Smeenk, Chris (2021) Noether’s first theorem and the energy-momentum tensor ambiguity problem. The Physics and Philosophy of Noether’s Theorems.

Wave-Functionalism

Allori, Valia (2021) Wave-Functionalism. Synthese.

Understanding the Progress of Science

McCoy, C.D. (2021) Understanding the Progress of Science. [Preprint]

Testability and Viability: Is Inflationary Cosmology “Scientific”?

Dawid, Richard and McCoy, C.D. (2021) Testability and Viability: Is Inflationary Cosmology “Scientific”? [Preprint]

The Constitution of Weyl’s Pure Infinitesimal World Geometry

McCoy, C.D. (2021) The Constitution of Weyl’s Pure Infinitesimal World Geometry. [Preprint]

What eliminative materialism isn’t

Abstract

In this paper my aim is to get clearer on what eliminative materialism actually does and does not entail. I look closely at one cluster of views that is often described as a form of eliminativism in contemporary philosophy and cognitive science and try to show that this characterization is a mistake. More specifically, I look at conceptions of eliminativism recently endorsed by writers such as Edouard Machery (2009), Paul Griffiths (1997), Valerie Hardcastle (1999) and others, and argue that although these views do endorse the elimination of something, they offer only what I will call a sort of category dissolution, and should be treated as something altogether different from traditional eliminativism. Spelling out the main contrast(s) between eliminative materialism proper and this alternative view, and defending the need to keep them distinct, is my primary objective. As I show, a central irony is that proponents of the problematic outlook often insist that divergent things should not be classified together under a single label. By characterizing their own views as a form of eliminativism, they commit a fundamental error that they themselves argue should not be made. While my focus here is on eliminative materialism, the error I intend to highlight appears across various discussions about alleged eliminativism of all sorts of things.

Local causation

Abstract

The counterfactual and regularity theories are universal accounts of causation. I argue that these should be generalized to produce local accounts of causation. A hallmark of universal accounts of causation is the assumption that apparent variation in causation between locations must be explained by differences in background causal conditions, by features of the causal-nexus or causing-complex. The local account of causation presented here rejects this assumption, allowing for genuine variation in causation to be explained by differences in location. I argue that local accounts of causation are plausible, and have pragmatic, empirical and theoretical advantages over universal accounts. I then report on the use of presheaves as models of local causation. The use of presheaves as models of local variation has precedents in algebraic geometry, category theory and physics; they are here used as models of local causal variation. The paper presents this idea as stemming from an approach using presheaves as models of local truth. Finally, I argue that a proper balance between universal and local causation can be assuaged by moving from presheaves to fully-fledged sheaf models.

Consciousness and the Laws of Physics

Carroll, Sean M. (2021) Consciousness and the Laws of Physics. [Preprint]