Weekly Papers on Quantum Foundations (24)

Causality, unitarity and stability in quantum gravity: a non-perturbative perspective. (arXiv:2206.04072v1 [hep-th])

上午9:50|gr-qc updates on arXiv.org

Authors: Alessia Platania

Resumming quantum fluctuations at the level of the gravitational path integral is expected to result in non-local effective actions and thus in a non-trivial momentum dependence of the propagator. Which properties the (dressed) graviton propagator has to satisfy and whether they can all be met are key open questions. In this work we present criteria and conditions for the momentum dependence of a graviton propagator which is consistent with unitarity, causality, and stability in a non-perturbative setting. To this end, we revisit several aspects of these conditions, highlighting some caveats and subtleties that got lost in recent discussions, and spelling out others that to our best knowledge have not been studied in detail. We discuss the consequences of these concepts for the properties of the graviton propagator. Finally, we provide examples of propagators satisfying unitarity and causality, while avoiding tachyonic and vacuum instabilities, and allowing for an analytic Wick rotation.

On quantum states over time. (arXiv:2202.03607v2 [quant-ph] UPDATED)

上午9:50|James Fullwood, Arthur J. Parzygnat|quant-ph updates on arXiv.org

In 2017, D. Horsman, C. Heunen, M. Pusey, J. Barrett, and R. Spekkens proved that there is no physically reasonable assignment that takes a quantum channel and an initial state and produces a joint state on the tensor product of the input and output spaces. The interpretation was that there is a clear distinction between space and time in the quantum setting that is not visible classically, where in the latter, one can freely use Bayes’ theorem to go between joint states and marginals with noisy channels. In this paper, we prove that there actually is such a physically reasonable assignment, bypassing the no-go result of Horsman et al., and we illustrate that this is achievable by restricting the domain of their assignment to a domain which represents the given data more faithfully.

Quantum clones inside black holes. (arXiv:2206.04608v1 [gr-qc])

上午9:50|gr-qc updates on arXiv.org

Authors: Gerard t Hooft

A systematic procedure is proposed for better understanding the evolution laws of black holes in terms of pure quantum states. We start with the two opposed regions I and II in the Penrose diagram, and study the evolution of matter in these regions, using the algebra derived earlier from the the Shapiro effect in quantum particles. Since this spacetime has two distinct asymptotic regions, one must assume that there is a mechanism that reduces the number of states. In earlier work we proposed that region II describes the angular antipodes of region I , the ‘antipodal identification’, but this eventually leads to contradictions. Our much simpler proposal is now that all states defined in region II are exact quantum clones of those in region I . Not only does this make all physical states observable, but, most surprisingly, this suffices to restore unitarity as well.

Planckian discreteness as seeds for cosmic structure. (arXiv:2104.08881v3 [gr-qc] UPDATED)

上午9:50|gr-qc updates on arXiv.org

Authors: Lautaro AmadeiAlejandro Perez

We propose a model of inflation driven by the relaxation of an initially Planckian cosmological constant due to diffusion. The model can generate a (approximately) scale invariant spectrum of (adiabatic) primordial perturbations with the correct amplitudes and red tilt without an inflaton. The inhomogeneities observable in the CMB arise from those associated to the fundamental Planckian granularity that are imprinted into the standard model Higgs scalar fluctuations during the inflationary phase. The process admits a semiclassical interpretation and avoids the trans-Planckian problem of standard inflationary scenarios based on the role of vacuum fluctuations. The deviations from scale invariance observed in the CMB are controlled by the self coupling constant of the Higgs scalar of the standard model of particle physics. The thermal production of primordial black holes can produce the amount of cold dark matter required by observations. For natural initial conditions set at the Planck scale the amplitude and tilt of the power spectrum of perturbations observed at the CMB depend only on known parameters of the standard model such as the self coupling of the Higgs scalar and its mass.

Computational Advantage from a Quantum Superposition of Qubit Gate Orders

2022年6月10日 星期五 下午6:00|Martin J. Renner and Časlav Brukner|PRL: General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Author(s): Martin J. Renner and Časlav Brukner

In an ordinary quantum algorithm the gates are applied in a fixed order on the systems. The introduction of indefinite causal structures allows us to relax this constraint and control the order of the gates with an additional quantum state. It is known that this quantum-controlled ordering of gates …

[Phys. Rev. Lett. 128, 230503] Published Fri Jun 10, 2022

Book review of Eric Scerri’s The Periodic table, Its Story and Its Significance, OUP, 2007

2022年6月10日 星期五 上午1:07|Philsci-Archive: No conditions. Results ordered -Date Deposited.

Scerri, Eric (2008) Book review of Eric Scerri’s The Periodic table, Its Story and Its Significance, OUP, 2007. KNowledge Organization (35). pp. 251-255.

How was Nicholson’s highly inconsistent atomic theory able to yield explanatory as well as predictive success?

2022年6月10日 星期五 上午1:06|Philsci-Archive: No conditions. Results ordered -Date Deposited.

Scerri, Eric (2021) How was Nicholson’s highly inconsistent atomic theory able to yield explanatory as well as predictive success? Contemporary Scientific Realism: The Challenge from the History of Science.

Mario Bunge and Gustavo Romero on Gravitational Waves and Reality of Space: Towards Neo-Bungean Space(time) Structuralism

2022年6月10日 星期五 上午1:04|Philsci-Archive: No conditions. Results ordered -Date Deposited.

Taqatqeh, Yousef S. (2022) Mario Bunge and Gustavo Romero on Gravitational Waves and Reality of Space: Towards Neo-Bungean Space(time) Structuralism. [Preprint]

Quantum Information in Relativity: The Challenge of QFT Measurements

2022年6月10日 星期五 上午1:03|Philsci-Archive: No conditions. Results ordered -Date Deposited.

Charis, Anastopoulos and Konstantina, Savvidou (2021) Quantum Information in Relativity: The Challenge of QFT Measurements. Entropy, 24 (4). ISSN 1099-4300

Is retrocausal quantum mechanics consistent with special relativity?

2022年6月8日 星期三 下午2:30|Philsci-Archive: No conditions. Results ordered -Date Deposited.

Gao, Shan (2022) Is retrocausal quantum mechanics consistent with special relativity? Foundations of Physics. ISSN 0015-9018

The preferred basis problem in the many-worlds interpretation of quantum mechanics: why decoherence does not solve it

2022年6月8日 星期三 上午8:00|Latest Results for Synthese


We start by very briefly describing the measurement problem in quantum mechanics and its solution by the Many Worlds Interpretation (MWI). We then describe the preferred basis problem, and the role of decoherence in the MWI. We discuss a number of approaches to the preferred basis problem and argue that contrary to the received wisdom, decoherence by itself does not solve the problem. We address Wallace’s emergentist approach based on what he calls Dennett’s criterion, and we compare the logical structure of Wallace’s argument that the Hilbert space structure and the unitary dynamics should be considered a complete description of the physics of the universe with the logical structure of the EPR argument against the completeness of quantum mechanics. Then, we consider the nature of so-called “high level emergent facts” and Dennett’s criterion in Wallace’s approach and we discuss the implications of its non-reductive nature. Finally, we conclude that (contrary to the received wisdom) the MWI is not a straightforward interpretation of pure quantum mechanics that doesn’t add anything to it. Whether or not it is more parsimonious than other quantum mechanical theories (such as the GRW theory and Bohm’s theory) depends on the details of the additions.

Seeing colours unconsciously

2022年6月7日 星期二 上午8:00|Latest Results for Synthese


According to unconscious perception hypothesis (UP), mental states of the same fundamental kind as ordinary conscious seeing can occur unconsciously. The proponents of UP often support it with empirical evidence for a more specific hypothesis, according to which colours can be seen unconsciously (UPC). However, UPC is a general claim that admits of many interpretations. The main aim of this paper is to determine which of them is the most plausible. To this end, I investigate how adopting various conceptions of colour and perceptual phenomenal character affects UPC’s resilience to objections. This brings me to the conclusion that the most plausible reading of UPC is the one according to which the phenomenal character of colour perception (i) is constituted by colours qua primitive mind-independent qualities of the environment and (ii) is not essentially tied to consciousness. My conclusion not only identifies the most plausible interpretation of UPC, but also highlights and supports an unorthodox version of the relational theory of perception, which is a perfectly viable yet so far overlooked stance in the debate about unconscious perception.

Locality resolved

2022年6月6日 星期一 上午8:00|Lothar Wondraczek|Nature Physics – Issue – nature.com science feeds

Nature Physics, Published online: 06 June 2022; doi:10.1038/s41567-022-01636-6

Two-dimensional model glasses exhibit characteristics in their low-frequency vibrational density of states that can be traced to the quasilocalized dynamics of string-like objects. This finding provides an explanation for a universal feature of glasses known as the boson peak.

How Analogy Helped Create the New Science of Thermodynamics

2022年6月5日 星期日 下午3:22|Philsci-Archive: No conditions. Results ordered -Date Deposited.

Norton, John D. (2022) How Analogy Helped Create the New Science of Thermodynamics. [Preprint]

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