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Authored Books

Näger, Paul M. (forthcoming). Quantum Entanglement and Causation. Boston Studies in the Philosophy of Science. Cham: Springer.
Friebe, C., M. Kuhlmann, H. Lyre, P. M. Näger, O. Passon and M. Stöckler. Philosophie der Quantenphysik. Heidelberg: Springer Spektrum.

Dieses Buch liefert dem Leser eine aktuelle und fundierte Einführung in die Philosophie der Quantenphysik. Obwohl sich die Quantentheorie durch spektakuläre empirische Erfolge auszeichnet, wird bis heute kontrovers diskutiert, wie sie zu verstehen ist. In diesem Werk geben die Autoren einen Überblick über die zahlreichen philosophischen Herausforderungen: Verletzen Quantenobjekte das Prinzip der Kausalität? Sind gleichartige Teilchen ununterscheidbar und daher keine Individuen? Behalten Quantenobjekte in der zeitlichen Entwicklung ihre Identität? Wie verhält sich ein zusammengesetztes Quantensystem zu seinen Teilen? Diese Fragen werden im Rahmen verschiedener Deutungsansätze der Quantentheorie diskutiert. Ein Ausblick in die Quantenfeldtheorie verschärft das Hauptproblem der Nichtlokalität.
Philosophie der Quantenphysik richtet sich an Philosophen mit Interesse für Physik, macht Physiker mit den philosophischen Fragen ihres Faches vertraut und liefert Anregungen für den gymnasialen Physik-Unterricht. Das Buch schließt damit eine Lücke zwischen populären Einführungen und spezialisierten Monografien zur Philosophie der Quantenphysik. In der vorliegenden zweiten Auflage wurde das Kapitel zu Verschränkung und Nicht-Lokalität deutlich erweitert und jedes Kapitel mit Übungsaufgaben und Musterlösungen ergänzt.

2015: 1st edition
2018: 2nd edition (revised and enlarged)
English version: Friebe, C., M. Kuhlmann, H. Lyre, P. M. Näger, O. Passon and M. Stöckler (2018). Philosophy of Quantum Physics. Cham: Springer International. (Translation of the 2nd German ed., trans. W. D. Brewer)

This book provides a thorough and up-to-date introduction to the philosophy of quantum physics. Although quantum theory is renowned for its spectacular empirical successes, controversial discussion about how it should be understood continue to rage today. In this volume, the authors provide an overview of its numerous philosophical challenges: Do quantum objects violate the principle of causality? Are particles of the same type indistinguishable and therefore not individual entities? Do quantum objects retain their identity over time? How does a compound quantum system relate to its parts? These questions are answered here within different interpretational approaches to quantum theory. Finally, moving to Quantum Field Theory, we find that the problem of non-locality is exacerbated.
Philosophy of quantum physics is aimed at philosophers with an interest in physics, while also serving to familiarize physicists with many of the essential philosophical questions of their subject.


Edited Books

Jansen, Ludger, and Paul M. Näger (2018). Peter van Inwagen: Materialism, Free Will, and God. Cham: Springer.

This book discusses the philosophy of influential contemporary philosopher Peter van Inwagen. Looking at perennial philosophical problems from a modern point of view, Peter van Inwagen’s philosophy masterfully combines positions that have been considered irreconcilable: incompatibilism concerning free will, materialism, organicism, theism and realism concerning fictional entities. As readers will discover, his arguments are witty, surprising and deep.
The book includes Peter van Inwagen’s Münster Lecture of 2015 on free will, as well as eleven papers from the Münster colloquium discussing central themes of his philosophy, and a reply to each paper by Peter van Inwagen himself. Introducing his philosophy and relating his work to other contemporary views, this book is of interest to graduate students and professionals in philosophy alike.


Articles in Journals

Näger, Paul M. (under review). The Mereological Problem of Entanglement. Preprint.

It is well-known that the entangled quantum state of a composite object cannot be reduced to the states of its parts. This quantum holism provides a peculiar challenge to formulate an appropriate mereological model: When a system is in an entangled state, which objects are there on the micro and macro level, and which of the objects carries which properties? This paper chooses a modeling approach to answer these questions: It proceeds from a systematic overview of consistent mereological models for entangled systems and discusses which of them is compatible with the quantum mechanical evidence (where quantum states are understood realistically). It reveals that entangled quantum systems neither describe undivided wholes nor objects that stand in irreducible relations. The appropriate model assumes that the entangled property is an irreducible non-relational plural property carried collectively by the micro objects, while there is no macro object. In this sense, quantum holism is an instance of property holism, not of object holism.

Näger, Paul M., and Niko Strobach (under review). A Taxonomy for the Mereology of Entangled Quantum Systems. Preprint.

The emerging field of quantum mereology considers part-whole relations in quantum systems. Entangled quantum systems pose a peculiar problem in the field, since their total states are not reducible to that of their parts. While there exist several established proposals for modelling entangled systems, like monistic holism or relational holism, there is considerable unclarity, which further positions are available. Using the lambda operator and plural logic as formal tools, we review and develop conceivable models and evaluate their consistency and distinctness. The main result is an exhaustive taxonomy of six distinct and precise models that both provide information about the mereological features as well as about the entangled property. The taxonomy is well-suited to serve as the basis for future systematic investigations.

Näger, Paul M. (2022). Evidence for Interactive Common Causes. Resuming the Cartwright–Hausman–Woodward debate. European Journal for Philosophy of Science. 12(1): 2. [OA]

The most serious candidates for common causes that fail to screen off (‘interactive common causes’, ICCs) and thus violate the causal Markov condition (CMC) refer to quantum phenomena. In her seminal debate with Hausman and Woodward, Cartwright early on focussed on unfortunate non-quantum examples. Especially, Hausman and Woodward’s redescriptions of quantum cases saving the CMC remain unchallenged. This paper takes up this lose end of the discussion and aims to resolve the debate in favour of Cartwright’s position. It systematically considers redescriptions of ICC structures, including those by Hausman and Woodward, and explains why these are inappropriate, when quantum mechanics (in an objective collapse interpretation) is true. It first shows that all cases of purported quantum ICCs are cases of entanglement and then, using the tools of causal modelling, it provides an analysis of the quantum mechanical formalism for the case that the collapse of entangled systems is best described as a causal model with an ICC.

Näger, Paul M. (2020). A Stronger Bell Argument for (Some Kind of) Parameter Dependence. Studies in the History and Philosophy of Modern Physics. 72, 1–28. [Preprint]

It is widely accepted that the violation of Bell inequalities excludes local theories of the quantum realm. This paper presents a new derivation of the inequalities from non-trivial non-local theories and formulates a stronger Bell argument excluding also these non-local theories. Taking into account all possible theories, the conclusion of this stronger argument provably is the strongest possible consequence from the violation of Bell inequalities on a qualitative probabilistic level (given usual background assumptions). Among the forbidden theories is a subset of outcome dependent theories showing that outcome dependence is not sufficient for explaining a violation of Bell inequalities. Non-local theories which can violate Bell inequalities (among them quantum theory) are rather characterised by the fact that at least one of the measurement outcomes in some sense (which is made precise) probabilistically depends both on its local as well as on its distant measurement setting (‘parameter’). When Bell inequalities are found to be violated, the true choice is not ‘outcome dependence or parameter dependence’ but between two kinds of parameter dependences, one of them being what is usually called ‘parameter dependence’. Against the received view established by Jarrett and Shimony that on a probabilistic level quantum non-locality amounts to outcome dependence, this result confirms and makes precise Maudlin’s claim that some kind of parameter dependence is required.

Näger, Paul M. (2016). The Causal Problem of Entanglement. Synthese 193(4), 1127–1155.

This paper expounds that besides the well-known spatio-temporal problem there is a causal problem of entanglement: even when one neglects spatio-temporal constraints, the peculiar statistics of EPR/B experiment is inconsistent with usual principles of causal explanation as stated by the theory of causal Bayes nets. The conflict amounts to a dilemma that either there are uncaused correlations (violating the causal Markov condition) or there are caused independences (violating the causal faithfulness condition). I argue that the central ideas of causal explanations can be saved if one accepts the latter horn and explains the unfaithful independences by a stable fine-tuning of the causal parameters.

Thomas R. Einert, Paul M. Näger, Henri Orland, and Roland R. Netz (2008). Impact of loop statistics on the Thermodynamics of RNA folding. Physical Review Letters 101(4), 048103.

Loops are abundant in native RNA structures and proliferate close to the unfolding transition. By including a statistical weight ~l–c for loops of length l in the recursion relation for the partition function, we show that the heat capacity depends sensitively on the presence and value of the exponent c, even for a short explicit tRNA sequence. For long homo-RNA, we analytically calculate the critical temperature and critical exponents which exhibit a nonuniversal dependence on c.


Articles in Books

Paul M. Näger (2020) Was ist ein Naturgesetz? Nancy Cartwright [What Is a Law of Nature? Nancy Cartwright]. In Müller-Salo, Johannes (ed.), Analytische Philosophie, UTB, 57–76.

In unserer Welt laufen Vorgänge nicht beliebig, sondern nach ganz bestimmten Regeln ab („Naturgesetze“). Was genau ein Gesetz ist, ist eine viel diskutierte Frage in der zeitgenössischen analytischen Philosophie, insbesondere in den Disziplinen Wissenschaftsphilosophie und Metaphysik. Dabei gibt es drei Hauptfragen: Erstens die begriffliche Frage, welche Bedingungen eine Regel genau erfüllen muss, um als Naturgesetz zu gelten. Zweitens die metaphysische Frage, was ein Naturgesetz ist, d.h. worauf in der Welt sich Aussagen über Regelmäßigkeiten beziehen. Davon zu unterscheiden, drittens, ist die hier nicht behandelte epistemische Frage, wie man erkennt, ob eine Gesetzeshypothese wahr ist.

In diesem Aufsatz werden wir uns die Antworten der zeitgenössischen US-amerikanischen Wissenschaftsphilosophin Nancy Cartwright auf diese Fragen ansehen. Cartwright wird den bedeutendsten Köpfen der Wissenschaftsphilosophie unserer Zeit zugerechnet und hat sich in ihrem Werk immer wieder mit der Frage nach Gesetzen beschäftigt. Ihre Antwort ist deshalb interessant, weil sie auf eine Reihe von Schwierigkeiten der seit vielen Jahrzehnten vorherrschenden Sicht auf Gesetze, des humeschen Empirismus, hinweist und eine originelle Alternativposition entwickelt. Dieser Aufsatz ist in zwei Hauptteile gegliedert. Um die Pointen von Cartwrights Position verständlich zu machen, stelle ich in einem ersten Teil zunächst die in der zeitgenössischen Wissenschaftsphilosophie vorherrschende neo-humeanische Sicht von Naturgesetzen vor (Abschnitt 4.2). Diese bietet dann die Kontrastfolie für Cartwrights Position, die ich im zweiten Teil präsentiere (Abschnitt 4.3).

Husmann, Julian, and Paul M. Näger (2018) Physical Composition by Bonding. In L. Jansen & P. M. Näger (ed.), Peter van Inwagen: Materialism, Free Will, and God, Springer, 65–96. [Preprint]

Van Inwagen proposes that besides simples only living organisms exist as composite objects. This paper suggests expanding van Inwagen’s ontology by also accepting composite objects in the case that physical bonding occurs (plus some extra conditions). Such objects are not living organ-isms but rather physical bodies. They include (approximately) the complete realm of inanimate ordinary objects, like rocks and tables, as well as inanimate scientific objects, like atoms and molecules, the latter filling the ontological gap between simples and organisms in van Inwagen’s original picture. We thus propose a compositional pluralism claiming that composition arises if and only if bonding or life occurs.

Leonhard, Gordon, Paul M. Näger and Andreas Schäfers (2016). Causation, Constitution and Existence. In A. Bahr & M. Seidl (ed.), Ernest Sosa: Targeting his Philosophy, Springer, 85–99.

Contemporary debates about mechanisms in the philosophy of science raise the question about the relation between constitutive and causal relations. These discussions so far have not received Ernest Sosa’s “Varieties of Causation” (1980), which addresses similar questions from a metaphysical point of view. The present paper reconstructs and evaluates Sosa’s arguments from the perspective of the contemporary debates. We argue that while Sosa’s arguments are probably not suited to advance the current debate, his claim that there are different varieties of causation might be an interesting idea to consider for those who assume that there are inter-level causal relations

Näger, Paul M., and Manfred Stöckler (2015). Verschränkung und Nicht-Lokalität: EPR, Bell und die Folgen. In C. Friebe et al., Philosophie der Quantenphysik, Springer Spektrum.
2015: 1st German edition, 113–176.
2018: 2nd German edition (revised and enlarged version), 107–185.

Verschränkte Zustände sind einer der charakteristischen Züge der Quantenphysik, für die es weder eine Entsprechung in der klassischen Physik noch in der alltäglichen Erfahrungswelt gibt. In diesem Kapitel umreißen wir historisch und systematisch die Debatte um diese besonderen Zustände. Wir stellen ihren Ursprung in einem Argument von Einstein, Podolsky und Rosen für die Unvollständigkeit der Quantenmechanik dar und zeigen, warum dieses Argument einerseits heute nicht mehr als überzeugend betrachtet wird, andererseits dennoch bis in aktuelle Debatten hinein nachwirkt. In einem zweiten Teil geben wir einen systematischen überblick über die zeitgenössischen Debatten zu Verschränkung, die sich um Bells Theorem und dessen Konsequenzen drehen. Einer klaren Darstellung des Theorems und seiner Voraussetzungen auf verschiedenen Ebenen folgt eine Diskussion der möglichen Konsequenzen. Detailliert wird die meist angeführte Konsequenz einer Nicht-Lokalität analysiert und in Beziehung zu Begriffen wie „Nicht-Separabilität“ und „Holismus“ gesetzt. Besonderes Augenmerk liegt auf der Frage, ob die Phänomene verschränkter Zustände kausal erklärt werden können und ob der zentrale Konflikt einer Nicht-Lokalität mit der Relativitätstheorie gelöst werden kann.

English version: Näger, Paul M., and Manfred Stöckler (2018). Entanglement and Non-Locality: EPR, Bell and the Consequences. In C. Friebe et al., Philosophy of Quantum Physics, Springer. (Translation of the 2nd German ed., trans. W. D. Brewer)

Entangled states are a specific feature of quantum physics that neither have a counterpart in classical physics nor in the realm of our ordinary experiences. In this chapter we outline the debate about these particular states both historically and systematically. We delineate how the debate originated in an argument for the incompleteness of quantum mechanics by Einstein, Podolsky and Rosen, and we show why, on the one hand, the argument is not considered convincing today, on the other hand, however, still affects present discussions. In a second part we give a systematic overview over the contemporary debate on entanglement which focusses on Bell’s theorem and its consequences. Discerning different levels, we reconstruct the theorem and its premises in a clear way and discuss possible consequences. We analyze in detail the received view that Bell’s theorem implies non-locality and relate it to concepts such as “non-separability” and “holism”. Especially we examine the question whether the phenomena involving entangled systems can be explained causally and whether the central conflict between a non-locality and the theory of relativity can be solved.


Reviews and Reports

Näger, Paul M. (2012). Review of C. A. Fuchs, Coming of Age with Quantum Information. Physik Journal 11 (3).
Kuhlmann, Meinard, Paul M. Näger, and Werner Stelzner (2011).  Report: GAP.7: Reflections and Projections: Challenges to Philosophy. Journal for General Philosophy of Science 42(1), 177–183.


Jansen, Ludger, and Paul M. Näger [in preparation]. Interview with Peter van Inwagen.