# Weekly Papers on Quantum Foundations (29)

Gomes, Henrique and Butterfield, Jeremy (2022) How to Choose a Gauge? The case of Hamiltonian Electromagnetism.

Gao, Shan (2022) If the global phase is real. [Preprint]

An Armstrongian Defense of Dispositional Monist Accounts of Laws of Nature

Mohammadian, Mousa (2022) An Armstrongian Defense of Dispositional Monist Accounts of Laws of Nature. [Preprint]

A reductive account of “before”: deriving temporal succession

Saudek, Daniel (2021) A reductive account of “before”: deriving temporal succession. [Preprint]

Warp Drive Aerodynamics. (arXiv:2207.06458v1 [gr-qc])

In this work we analyse the potential for a warp drive spacetime to develop instabilities due to the presence of quantum matter. Particularly, we look for points of infinite blueshift (which are analogous to points of a black hole inner horizon, known for its semiclassical instability), and categorise them through the behaviour of geodesics in their vicinity. We find that warp-drive bubbles in dimension 2+1 or higher are in fact likely to be stable, as they generally contain only isolated points where divergences are approached, leading to a finite limit for the overall accumulation of destabilising energy. Furthermore, any semiclassical instabilities in the warp drive due to energy-density buildups can be further diminished with particular, more “aerodynamic” shapes and trajectories for the drive.

A time-symmetric soliton dynamics \a la de Broglie. (arXiv:2207.06809v1 [quant-ph])

In this work we develop a time-symmetric soliton theory for quantum particles inspired from works by de Broglie and Bohm. We consider explicitly a non-linear Klein-Gordon theory leading to monopolar oscillating solitons. We show that the theory is able to reproduce the main results of the pilot-wave interpretation for non interacting particles in a external electromagnetic field. In this regime, using the time symmetry of the theory, we are also able to explain quantum entanglement between several solitons and we reproduce the famous pilot-wave nonlocality associated with the de Broglie-Bohm theory.

A possible solution to the which-way problem of quantum interference. (arXiv:2111.03203v4 [quant-ph] UPDATED)

It is commonly assumed that the observation of an interference pattern is incompatible with any information about the path taken by a quantum particle. Here we show that, contrary to this assumption, the experimentally observable effects of small polarization rotations applied in the slits of a double slit experiment indicate that individual particles passing the slits before their detection in the interference pattern are physically delocalized with regard to their interactions with the local polarization rotations. The rate at which the polarization is flipped to the orthogonal state is a direct measure of the fluctuations of the polarization rotation angles experienced by each particle. Particles detected in the interference maxima experience no fluctuations at all, indicating a presence of exactly one half of the particle in each slit, while particles detected close to the minima experience polarization rotations much larger than the local rotations, indicating a negative presence in one of the slits and a presence of more than one in the other.

Quantum Origin of (Newtonian) Mass and Symmetry for Lorentz Covariant Physics. (arXiv:2112.10597v2 [quant-ph] UPDATED)

The Galilean symmetry and the Poincare symmetry are usually taken as the fundamental (relativity) symmetries for nonrelativistic’ and relativistic’ physics, respectively, quantum or classical. Our fully group theoretical formulation approach to the theories, together with its natural companion of mechanics from symplectic geometry, ask for different perspectives. We present a sketch of the full picture here, emphasizing aspects which are different from the more familiar picture. The letter summarizes our earlier presented formulation while focusing on the part beyond, with an adjusted, or corrected, identification of the basic representations having the (Newtonian) mass as a Casimir invariant. Discussion on the limitations of the Poincare symmetry for the purpose is particularly elaborated.

Hidden Quantum Memory: Is Memory There When Somebody Looks?. (arXiv:2204.08298v2 [quant-ph] UPDATED)

In classical physics, memoryless processes and Markovian statistics are one and the same. This is not true for quantum processes, first and foremost due to the fact that quantum measurements are invasive. Independently of measurement invasiveness, here we derive a novel distinction between classical and quantum processes, namely the possibility of hidden quantum memory. While Markovian statistics of classical processes can always be reproduced by a memoryless dynamics, our main result establishes that this is not the case in quantum mechanics: We first provide an example of quantum non-Markovianity that depends on whether or not a previous measurement is performed — a phenomenon that is impossible for memoryless processes; we then strengthen this result by demonstrating statistics that are Markovian independent of how they are probed, but are are nonetheless still incompatible with memoryless quantum dynamics. Thus, we establish the existence of Markovian statistics that fundamentally require quantum memory for their creation.

Completing the quantum ontology with the electromagnetic zero-point field. (arXiv:2207.06549v1 [quant-ph])

Authors: Luis de la PeñaAna María Cetto

This text begins with a series of critical considerations on the initial interpretation of quantum phenomena observed in atomic systems. The bewildering explanations advanced during the construction of quantum mechanics are shown to have distanced the new theory from the rest of scientific knowledge, by introducing indeterminism, acausality, nonlocality, and even subjectivism as part of its interpretative framework. The conclusion drawn from this unsatisfactory interpretative landscape is that quantum mechanics lacks a key ontological ingredient. Arguments are given in favour of the random zero-point radiation field (ZPF) as the element needed to complete the quantum ontology. The (wave-mediated) quantum stochastic process is shown to be essentially different from Brownian motion, and more amenable to an analogy with the hydrodynamic case. The new perspective provided by the introduction of the ZPF is used to explain some salient features of quantum systems, such as the stationary atomic states and the transitions between them, and the apparent nonlocality expressed in the entangled states. Notably, the permanent presence of the field drastically affects the dynamics of the (otherwise classical) particle, which eventually falls under the control of the field. This qualitative change is reflected in the transition from the initial classical description in space-time, to the final quantum one in the Hilbert space. The clarification of the mechanism of quantization leads us to consider the possibility that a similar phenomenon occurs in other physical systems of corpuscles subjected to an oscillating background, of which the walking-droplet system is a paradigmatic example.

Cosmology as a Crossed Product. (arXiv:2207.06704v1 [hep-th])

Authors: Cesar Gomez

We suggest a new conceptual frame where inflationary Cosmology is quantum mechanically described using the Hilbert space representation of the crossed product of the type $III$ factor associated with the algebra of local operators on the de Sitter static patch and the automorphism of translations in the emergent conformal time. In this formal framework scalar curvature fluctuations are determined by the gravitational potential induced by the quantum variance of the generator of the conformal time automorphisms. Choosing as representative, in the Hilbert space of the crossed product, the effective vacuum state for each mode and conformal time, we evaluate the quantum variance and the induced scalar curvature fluctuations. This leads to a model independent characterization of the inflationary parameters (1-n_s) \sim 0.0318 and \epsilon\sim 0.0027 in good agreement with Planck experimental results. In this formal frame inflation extends the algebra of observables in a primordial dS expanding Universe. In this extension time evolution becomes an inner automorphism and the conjugated energy fluctuations manifest as the observable scalar curvature fluctuations.

Cosmological constant and equation of state of the quantum vacuum. (arXiv:2207.07111v1 [gr-qc])

Recent studies of quantum field theory in FLRW spacetime suggest that the cause of the speeding up of the universe is the quantum vacuum, no need to introduce ad hoc scalar fields. Appropriate renormalization of the energy-momentum tensor shows that the vacuum energy density is a smooth function of the Hubble rate and its derivatives: $\rho_{\rm vac}=\rho_{\rm vac}(H, \dot{H},\ddot{H},…)$. This is because in QFT the quantum scaling of $\rho_{\rm vac}$ with the renormalization point turns into cosmic evolution with $H$. As a result, any two nearby points of the cosmic expansion during the standard FLRW epoch are smoothly related through $\delta\rho_{\rm vac}\sim {\cal O}(H^2)$. In this scenario, no fine tuning is needed at all. What we call the cosmological constant’ $\Lambda$ is just the nearly sustained value of $\rho_{\rm vac}(H)$ around (any) given epoch. In the very early universe, higher (even) powers $\rho_{\rm vac}\sim{\cal O}(H^N)$ ($N=4,6,..$) triggered fast inflation during a short period in which $H=$const. In it, the equation of state (EoS) of the vacuum is very close to $w_{\rm vac}=-1$, but this ceases to be true during the FLRW era. Amazingly, the quantum vacuum acts as a formidable cosmic chameleon: it subsequently adopts the EoS of matter during the relativistic ($w_{\rm vac}=1/3$) and non-relativistic ($w_{\rm vac}=0$) epochs, and in the late universe it mimics quintessence, $w_{\rm vac}\gtrsim-1$, only to tend again to $-1$ in the remote future. In the transit, the quantum vacuum helps to solve the $H_0$ and $\sigma_8$ tensions.

Phenomenology of Holography via Quantum Coherence on Causal Horizons. (arXiv:2204.12080v2 [gr-qc] UPDATED)

Authors: Ohkyung Kwon

There is much recent development towards interferometric measurements of holographic quantum uncertainties in an emergent background space-time. Despite increasing promise for the target detection regime of Planckian strain spectral density, the latest motivating theoretical ideas have not been connected to a phenomenological model of observables measured in a realistic experiment. This manuscript proposes a candidate model, based on the central hypothesis that all horizons are universal boundaries of coherent quantum information — where the decoherence of space-time happens for the observer. The prediction is motivated by ‘t Hooft’s algebra for black hole information that gives coherent states on horizons, whose spatial correlations were shown by Verlinde and Zurek to also appear on holographic fluctuations of causal boundaries in flat space-time (conformal Killing horizons). Time-domain correlations are modeled from Planckian jitters whose coherence scales match causal diamonds, motivated by Banks’ framework for the emergence of space-time and locality. The universality of this coherence on causal horizons compels a multimodal research program probing concordant signatures: An analysis of cosmological data to probe primordial correlations, motivated by Hogan’s interpretation of well-known CMB anomalies as coherent fluctuations on the inflationary horizon, and upcoming 3D interferometers to probe causal diamonds in flat space-time. Candidate interferometer geometries are presented, with a modeled frequency spectrum for each design.

Time-reversal-based quantum metrology with many-body entangled states

Nature Physics, Published online: 14 July 2022; doi:10.1038/s41567-022-01653-5

The standard quantum limit bounds the precision of quantum measurements. Now, a protocol based on time-reversal operations with cold atoms overcomes that limit and achieves the greatest phase sensitivity improvement in any full Ramsey interferometer.

The Epistemic Privilege of Measurement: Motivating a Functionalist Account

Ohnesorge, Miguel (2022) The Epistemic Privilege of Measurement: Motivating a Functionalist Account. In: UNSPECIFIED.

On Theoretical Contingency of Quantum Mechanics

Jamali, Alireza (2022) On Theoretical Contingency of Quantum Mechanics. [Preprint]

On the unreasonable reliability of mathematical inference

Larvor, Brendan (2022) On the unreasonable reliability of mathematical inference. [Preprint]

From probabilistic topologies to Feynman diagrams: Hans Reichenbach on time, genidentity, and quantum physics

Abstract

Hans Reichenbach’s posthumous book The Direction of Time ends somewhere between Socratic aporia and historical irony. Prompted by Feynman’s diagrammatic formulation of quantum electrodynamics, Reichenbach eventually abandoned the delicate balancing between the macroscopic foundation of the direction of time and microscopic descriptions of time order undertaken throughout the previous chapters in favor of an exclusively macroscopic theory that he had vehemently rejected in the 1920s. I analyze Reichenbach’s reasoning against the backdrop of the history of Feynman diagrams and the current practice of particle physics. Building upon the debates about processes and conserved quantities between Wesley Salmon and Phil Dowe in the 1990s, and the exchange between Reichenbach and the gestalt theorist Kurt Lewin during the 1920s about topology and genidentity, I investigate whether the aporia about local time order could be avoided by following a strategy that Reichenbach adopted elsewhere in the book and develop a notion of functional genidentity that captures the practice of present-day elementary particle physics and the fact that Feynman diagrams have to be understood in the context of a complex mathematical description of scattering processes.