The article 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, as well as holistic, and discuss two metaphysical options to conceive them, namely, Humeanism and modal realism in the guise of dispositionalism. 1 Introduction2 Primitive Ontology: Primitive Stuff3 The Physics of Matter as Primitive Stuff4 The Humean Best System Analysis of the Dynamical Variables5 Modal Realism about the Dynamical Variables6 Conclusion. (shrink)

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. (shrink)

We discuss Boltzmann’s probabilistic explanation of the second law of thermodynamics providing a comprehensive presentation of what is called today the typicality account. Countering its misconception as an alternative explanation, we examine the relation between Boltzmann’s H-theorem and the general typicality argument demonstrating the conceptual continuity between the two. We then discuss the philosophical dimensions of the concept of typicality and its relevance for scientific reasoning in general, in particular for understanding the reduction of macroscopic laws to microscopic laws. Finally, (...) we reply to various common criticisms of the typicality account. (shrink)

The paper provides a critical discussion of the Super-Humean view of spacetime and the “minimalist ontology” in terms of Leibnizian relations and primitive matter points, recently developed by Esfeld et al. It investigates, in particular, the empirical adequacy of the proposed metaphysics, arguing that Super-Humeanism cannot provide a plausible account of space and time without committing to bona fide geometric structure in the fundamental relations. Against this backdrop, I propose a moderate version of Super-Humeanism and discuss its possible application to (...) Euclidean space and General Relativity. (shrink)

We discuss the no-go theorem of Frauchiger and Renner based on an "extended Wigner's friend" thought experiment which is supposed to show that any single-world interpretation of quantum mechanics leads to inconsistent predictions if it is applicable on all scales. We show that no such inconsistency occurs if one considers a complete description of the physical situation. We then discuss implications of the thought experiment that have not been clearly addressed in the original paper, including a tension between relativity and (...) nonlocal effects predicted by quantum mechanics. Our discussion applies in particular to Bohmian mechanics. (shrink)

The article 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...

The paper discusses recent proposals by Carroll and Chen, as well as Barbour, Koslowski, and Mercati to explain the arrow of time without a Past Hypothesis, i.e. the assumption of a special 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. (shrink)

The paper uses the concept of typicality to spell out an argument against Humean supervenience and the best system account of laws. It proves that, in a very general and robust sense, almost all possible Humean worlds have no Humean laws. They are worlds of irreducible complexity that do not allow for any systematization. After explaining typicality reasoning in general, the implications of this result for the metaphysics of laws are discussed in detail.

Charlotte Werndl and Roman 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. This note points out conceptual confusions that could arise from their discussion, concerning, in particular, the authors’ use of “Boltzmann equilibrium.” It also clarifies the status of the Khinchin condition for the equivalence of Boltzmannian and Gibbsian equilibrium predictions and shows that it follows, under the assumptions proposed by Werndl and (...) Frigg, from standard arguments in probability theory. (shrink)

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.

The essay traces the following idea from the presocratic philosopher Heraclitus, to the Pythagoreans, to Newton’s Principia: Laws of nature are laws of proportion for matter in motion. Proportions are expressed by numbers or, as the essay proposes, even identical to real numbers. It is argued that this view is still relevant to modern physics and helps us understand why physical laws are mathematical.

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

AbstractBohmian 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.

Das vorliegende Buch richtet sich an Studierende der Physik, für die nach der Quantenmechanik-Vorlesung die wesentliche Frage offen geblieben ist: „Was sagt denn nun der mathematische Formalismus, den ich jetzt ausgiebig und ach so mühsam studiert habe, über die Natur aus?“. Bei der Suche nach der Antwort besprechen die Autoren unter anderem die modernen Quantentheorien, die von John Stuart Bell „Theorien ohne Beobachter“ genannt wurden: die Bohmsche Mechanik, die Kollaps-Theorie und die Viele-Welten-Theorie. -/- Neben zielgerichteten mathematischen Aussagen, die in Kursvorlesungen (...) selten vorkommen, erklärt das Buch anhand der neuen Theorien die Rolle der Wellenfunktion und des Zufalls in der Quantenmechanik. Insbesondere beschäftigen sich die Autoren auch mit der Gedankenwelt des Physikers John Stuart Bell, der mit den berühmten, aber leider oft missverstandenen Bellschen Ungleichungen unser physikalisches Weltbild nachhaltig verändert hat. Das Buch eignet sich damit begleitend oder ergänzend zu einer Kursvorlesung über Quantenmechanik oder aber auch zum Selbststudium. (shrink)

In a recent paper, 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 coincide. In this comment, I point out serious flaws in their work and try to put their results into proper context. I also clarify the concept of Boltzmann equilibrium, the status of the "Khinchin condition" and their connection to the law of large numbers.

This note clarifies several details about the description of the measurement process in Bohmian mechanics and responds to a recent preprint by Shan Gao, wrongly claiming a contradiction in the theory.