arXiv subjects

Dustin Lazarovici

Publications and source records attributed to Dustin Lazarovici.

18 recordsLinked to original sources

arXiv2026

Velocity of a Quantum Particle in a Classically Forbidden Region

Recently, Sharoglazova et al. [Nature 643, 67 (2025)] proposed a procedure for determining the speed of a quantum particle in the classically forbidden region of a potential step, and implemented it in a beautiful experiment. The inferred speeds disagree significantly with the Bohmian velocities, which the authors presented as an experimental challenge to Bohmian mechanics. This is puzzling because the speeds are inferred from particle populations in coupled waveguides for which Bohmian mechanics and standard quantum mechanics make identical predictions. We resolve the puzzle by a detailed theoretical analysis of the experimental setup. We show that the speed inference rests on an assumption that fails in the relevant (evanescent) regime according to both Bohmian mechanics and standard quantum mechanics -- namely that the inter-waveguide tunneling time is set by the transverse coupling and is not affected by entanglement with the longitudinal degree of freedom. We also consider a second speed estimate suggested by Sharoglazova et al., which is based on the B\"uttiker dwell time formula for particles in the forbidden region. We show that the authors applied the formula incorrectly, and that a correct application yields exact agreement with the predictions of Bohmian mechanics. Our analysis includes explicit calculations of Bohmian trajectories, dwell times, and longitudinal speeds in the two-dimensional waveguide model of the experiment.

quant-ph↗

arXiv2025

Comment on "Energy-speed relationship of quantum particles challenges Bohmian mechanics"

In their recent paper [Nature 643, 67 (2025)], Sharaglazova et al. report an optical microcavity experiment yielding an "energy-speed relationship" for quantum particles in evanescent states, which they infer from the observed population transfer between two coupled waveguides. The authors argue that their findings challenge the validity of Bohmian particle dynamics because, according to the Bohmian guiding equation, the velocities in the classically forbidden region would be zero. In this note, we explain why this claim is false and the experimental findings are in perfect agreement with Bohmian mechanics. We also clarify why the operationally defined speeds reported in the paper are unrelated to particle velocities in the sense described by Bohmian mechanics. In contrast to other recent replies, our analysis relies solely on the standard Bohmian guidance equation for single particles.

quant-ph↗

arXiv2022

The Point of Primitive Ontology

Bohmian mechanics grounds the predictions of quantum mechanics in precise dynamical laws for a primitive ontology of point particles. In an appraisal of the de-Broglie-Bohm theory, the paper discusses the crucial epistemological and conceptual role that a primitive ontology plays within a physical theory. It argues that quantum theories without primitive ontology fail to make contact with observable reality in a clear and consistent manner. Finally, it discusses Einstein's epistemological model and why it supports the primitive ontology approach.

physics.hist-ph↗

arXiv2020

Arrow(s) of Time without a Past Hypothesis

The paper discusses recent proposals by Carroll and Chen, as well as Barbour, Koslowski, and Mercati to explain the (thermodynamic) arrow of time without a Past Hypothesis, i.e., the assumption of a special (low-entropy) initial state of the universe. After discussing the role of the Past Hypothesis and the controversy about its status, we explain why Carroll's model - which establishes an arrow of time as typical - can ground sensible predictions and retrodictions without assuming something akin to a Past Hypothesis. We then propose a definition of a Boltzmann entropy for a classical $N$-particle system with gravity, suggesting that a Newtonian gravitating universe might provide a relevant example of Carroll's entropy model. This invites comparison with the work of Barbour, Koslowski, and Mercati that identifies typical arrows of time in a relational formulation of classical gravity on shape space. We clarify the difference between this gravitational arrow in terms of shape complexity and the entropic arrow in absolute spacetime and work out the key advantages of the relationalist theory. We end by pointing out why the entropy concept relies on absolute scales and is thus not relational.

physics.hist-ph↗

arXiv2019

Position Measurements and the Empirical Status of Particles in Bohmian Mechanics

The paper addresses the debate about the empirical status of particles versus wave functions in Bohmian quantum mechanics. It thereby clarifies questions and misconceptions about the role of the particles in the measurement process, the (un)reliability of position measurements ("surrealistic trajectories"), and the limited empirical access to particle positions ("absolute uncertainty"). Taking the ontological commitment of Bohmian mechanics seriously, all relevant empirical results follow from an analysis of the theory in terms of particle motions. Finally, we address the question, why particle motions rather than patterns in the wave function would be the supervenience base of conscious experience.

quant-ph↗

arXiv2018

On Boltzmann vs. Gibbs and the Equilibrium in Statistical Mechanics

In a recent article, Werndl and Frigg discuss the relationship between the Boltzmannian and Gibbsian framework of statistical mechanics, addressing in particular the question when equilibrium values calculated in both frameworks agree. In this paper, I address conceptual confusions that could arise from their discussion, concerning in particular the authors' use of "Boltzmann equilibrium". I also clarify the status of the Khinchin condition for the equivalence of Boltzmannian and Gibbsian, and show that it follows under the assumptions proposed by Werndl and Frigg from standard arguments in probability theory.

physics.hist-ph↗

arXiv2018

Quantum theory cannot consistently describe the use of itself

Quantum theory provides an extremely accurate description of fundamental processes in physics. It thus seems likely that the theory is applicable beyond the, mostly microscopic, domain in which it has been tested experimentally. Here we propose a Gedankenexperiment to investigate the question whether quantum theory can, in principle, have universal validity. The idea is that, if the answer was yes, it must be possible to employ quantum theory to model complex systems that include agents who are themselves using quantum theory. Analysing the experiment under this presumption, we find that one agent, upon observing a particular measurement outcome, must conclude that another agent has predicted the opposite outcome with certainty. The agents' conclusions, although all derived within quantum theory, are thus inconsistent. This indicates that quantum theory cannot be extrapolated to complex systems, at least not in a straightforward manner.

quant-ph↗

arXiv2018

Against Fields

Using the example of classical electrodynamics, I argue that the concept of fields as mediators of particle interactions is fundamentally flawed and reflects a misguided attempt to retrieve Newtonian concepts in relativistic theories. This leads to various physical and metaphysical problems that are discussed in detail. In particular, I emphasize that physics has not found a satisfying solution to the self-interaction problem in the context of the classical field theory. To demonstrate the superiority of a pure particle ontology, I defend the direct interaction theory of Wheeler and Feynman against recent criticism and argue that it provides the most cogent formulation of classical electrodynamics.

physics.hist-ph↗

arXiv2018

Observables and unobservables in quantum mechanics: How the no-hidden-variables theorems support the Bohmian particle ontology

The paper argues that far from challenging - or even refuting - Bohm's quantum theory, the no-hidden-variables theorems in fact support the Bohmian ontology for quantum mechanics. The reason is that (i) all measurements come down to position measurements and (ii) Bohm's theory provides a clear and coherent explanation of the measurement outcome statistics based on an ontology of particle positions, a law for their evolution and a probability measure linked with that law. What the no-hidden-variables theorems teach us is that (i) one cannot infer the properties that the physical systems possess from observables and that (ii) measurements, being an interaction like other interactions, change the state of the measured system.

quant-ph↗

arXiv2016

A mean field limit for the Vlasov-Poisson system

We present a probabilistic proof of the mean field limit and propagation of chaos $N$-particle systems in three dimensions with positive (Coulomb) or negative (Newton) $1/r$ potentials scaling like $1/N$ and an $N$-dependent cut-off which scales like $N^{-1/3+ ε}$. In particular, for typical initial data, we show convergence of the empirical distributions to solutions of the Vlasov-Poisson system with either repulsive electrical or attractive gravitational interactions.

math-ph↗

arXiv2016

From the universe to subsystems: Why quantum mechanics appears more stochastic than classical mechanics

By means of the examples of classical and Bohmian quantum mechanics, we illustrate the well-known ideas of Boltzmann as to how one gets from laws defined for the universe as a whole to dynamical relations describing the evolution of subsystems. We explain how probabilities enter into this process, what quantum and classical probabilities have in common and where exactly their difference lies.

quant-ph↗

arXiv2016

A particle approximation for the relativistic Vlasov-Maxwell dynamics

We present a microscopic derivation of the 3-dimensional relativistic Vlasov-Maxwell system as a combined mean field and point-particle limit of an $N$-particle system of rigid charges with $N$-dependent radius. The approximation holds for typical initial particle configurations, implying in particular propagation of chaos for the respective dynamics.

math-ph↗

arXiv2015

The Vlasov-Poisson dynamics as the mean field limit of extended charges

The paper treats the validity problem of the nonrelativistic Vlasov-Poisson equation in $d\geq 2$ dimensions. It is shown that the Vlasov-Poisson dynamics can be derived as a combined mean field and point-particle limit of an N-particle Coulomb system of extended charges. This requires a sufficiently fast convergence of the initial empirical distributions. If the electron radius decreases slower than $N^{-\frac{1}{d(d+2)}}$, the corresponding initial configurations are typical. This result entails propagation of molecular chaos for the respective dynamics

math-ph↗

arXiv2014

The physics and metaphysics of primitive stuff

The paper sets out a primitive ontology of the natural world in terms of primitive stuff, that is, stuff that has as such no physical properties at all, but that is not a bare substratum either, being individuated by metrical relations. We focus on quantum physics and employ identity-based Bohmian mechanics to illustrate this view, but point out that it applies all over physics. Properties then enter into the picture exclusively through the role that they play for the dynamics of the primitive stuff. We show that such properties can be local (classical mechanics), as well as holistic (quantum mechanics), and discuss two metaphysical options to conceive them, namely Humeanism and modal realism in the guise of dispositionalism.

physics.hist-ph↗

arXiv2014

Could time-symmetric interactions reconcile relativity and quantum non-locality?

We present a simple model demonstrating that time-symmetric relativistic interactions can account for correlations violating the Bell inequalities while avoiding conspiracies as well as the commitment to instantaneous influences. Based on an explicit statistical analysis of this model, we emphasize the essential virtues and problems of such an account and discuss its relation to Bell's theorem.

quant-ph↗

arXiv2014

The ontology of Bohmian mechanics

The paper points out that the modern formulation of Bohm's quantum theory known as Bohmian mechanics is committed only to particles' positions and a law of motion. We explain how this view can avoid the open questions that the traditional view faces according to which Bohm's theory is committed to a wave-function that is a physical entity over and above the particles, although it is defined on configuration space instead of three-dimensional space. We then enquire into the status of the law of motion, elaborating on how the main philosophical options to ground a law of motion, namely Humeanism and dispositionalism, can be applied to Bohmian mechanics. In conclusion, we sketch out how these options apply to primitive ontology approaches to quantum mechanics in general.

physics.hist-ph↗

arXiv2014

Why "noncommuting common causes" don't explain anything

In my commentary, I will argue that the conclusions drawn in the paper "Noncommutative causality in algebraic quantum field" theory by Gábor Hofer-Szabó (and similar publications) are incorrect. As proven by J.S. Bell, a local common causal explanation of correlations violating the Bell inequality is impossible.

quant-ph↗

arXiv2013

Time Evolution in the external field problem of Quantum Electrodynamics

A general problem of quantum field theories is the fact that the free vacuum and the vacuum for an interacting theory belong to different, non-equivalent representations of the canonical (anti-)commutation relations. In the external field problem of QED, we encounter this problem in the form that the Dirac time evolution for an external field with non-vanishing magnetic components will not satisfy the Shale-Stinespring condition, known to be necessary and sufficient for the existence of an implementation on the fermionic Fock space. Therefore, a second quantization of the time evolution in the usual way is impossible. In this thesis, we present several rigorous approaches to QED with time-dependent, external fields and analyze in what sense a time evolution can exist in the second quantized theory. We study different constructions of the fermionic Fock space and prove their equivalence. We study and compare the results of Deckert et. al. (2010), where the time evolution is realized as unitary transformations between time-varying Fock spaces, with those of Langmann and Mickelsson (1996), who construct a "renormalization" for the time evolution and present a method to fix the phase of the second quantized scattering operator by parallel transport in a principle fibre bundle over the restricted, general linear group acting on the fermionic Fock space. We provide rigorous proof for the fact that the second quantization by parallel transport preserves causality. These findings seem to refute claims made in Scharf (1995) that the phase of the second quantized S-matrix is essentially determined by the requirement of causality. We propose a simple solution to the problem of gauge anomalies in the procedure of Langmann and Mickelsson, showing that the second quantization of the scattering operator can be made gauge-invariant by using a suitable class of renormalizations.

math-ph↗