Colloquium

The biweekly RCNP colloquium will resume in September. It takes place on Mondays at 16:00 and comprises talks by invited speakers as well as RCNP members. For questions, please contact Kian Salimkhani.

When: See schedule below
Where: Erasmus building 18.02 (if not indicated differently)

Schedule

Convener: Kian Salimkhani

24 November 2025
Sanne Vergouwen (U Utrecht): Modelling Black Hole Mass
What does it mean to say that black holes have mass? Within the framework of general relativity, where black holes are described by vacuum equations, the answer to this question is far from trivial. In this talk, based on joint work with Niels Martens, I will argue that the concept of Schwarzschild black hole mass is best understood by considering five possible interpretations of the mass of a black hole. We adopt an approach similar to that of multiple modelling in science, which aims to improve understanding of highly complex systems or phenomena. In our case, the goal is to conceptualize a notion of mass that remains sufficiently close to the Newtonian conception while also applying accurately to black holes in general relativity. I will show, in particular, how a global interpretation of mass (such as the ADM mass) succeeds in referring to black hole mass and therefore deserves a place in our modelling framework, despite its significant departure from the traditionally local Newtonian conception. I then explore the implications of these multiple interpretations for the dichotomy between spacetime and matter. Mass is a key characteristic of matter, yet as vacuum solutions, black holes are often considered spacetime objects. Can black holes be both spacetime and matter? I will argue that the different interpretations supports abandoning the spacetime–matter dichotomy, both on a conceptual and a metaphysical level.

8 December 2025
Lucy James (U Bonn): Einstein's Platonism and Epistemology
During the later parts of his career, Einstein expressed what he called `Platonist' sentiments when reflecting on the process of discovery of his general theory of relativity. Einstein's shift to `Platonism' (expressed in 1933) from his earlier, more empiricist, standpoint has been documented by Norton (2000). In the first part of this talk, I give a more detailed characterisation of Einstein's views about the role of mathematical simplicity in physical theorising in terms familiar from the philosophy of mathematics, referring in particular to the philosophies of Poincaré and Wittgenstein (O'Gorman, 2001 and Dantzig, 1955). Metaphysical and epistemic components of Einstein's view, so characterised, are distinguished from its merely heuristic parts. Norton (Norton, 2000; Norton, 2020) claims that Einstein supplemented formal mathematical techniques with physical approaches. This project aims to add more detail to what is meant by `physical approaches'. A key point is that the role of features (like generality) of the modelling problem to be solved must be understood, in addition to features (like simplicity) of the available mathematical techniques. Finally, I will connect these thoughts to more modern uses of symmetry groups (e.g. in gauge theory - see Gomes 2024), claiming that either implicit or explicit notions of mathematical simplicity and generality continue to be epistemically guiding.

12 January 2026
Ruward Mulder (U California, Irvine): tba

26 January 2026
Maren Bräutigam (U Cologne): tba

9 February 2026
Fleur Hubau (RCNP): tba

2 March 2026
Shelly Yiran Shi (UC San Diego/U Oxford): tba

16 March 2026
Robert van Leeuwen (UvA): tba

Past speakers

If available, recordings are linked in the title.

2025

Convener: Kian Salimkhani

3 November 2025
Guy Hetzroni (The Open U of Israel): The Projectability of Meta-Inductive Arguments: The Case of Invariance Considerations
Meta-inductive argumentation is a suggested way of motivating proposed theories and research programs and evaluating their epistemic status based on the similarity of the theoretical methods they apply to theoretical methods that have led to empirically established theories. Meta-induction, together with other suggested approaches to theory assessment in the absence of empirical input, has invoked controversy, reflecting on the compatibility of theoretical practices in certain approaches to fundamental physics with familiar empirical standards of science (see, e.g., Dawid, 2013; Dardashti, Dawid and Thébault, 2019). The presented research suggests a refined approach toward these issues by introducing the notion of projectability of meta-inductive arguments. The analysis is by analogy to the discourse on scientific induction, in particular in the context of suggested naturalist solutions (e.g. by Quine, 1970; Boyd, 1991) to Goodman’s new riddle of induction. The analogy would be used to suggest a naturalist account of meta-induction, in terms of a reflective inductive-like inference on the scientific process itself. A notion of projectability is required, as given theoretical methods can be described and classified in numerous ways. Like in the case of naturalist accounts of scientific induction, this notion should be based on scientific knowledge expressed in background theories. More specifically, it is argued that projectable meta-induction is based on a reconstruction of theoretical methods used in established theories, in a way that maximizes the weight of evidence and its direct theoretical representation. Thus, projectable meta-induction is based on similarity between patterns of inference and filling of explanatory gaps, rather than on similarity between theoretical or mathematical concepts.
The account would be demonstrated using two examples involving invariance argument: the construction of gauge theories of gravity, and gauge invariant approaches to particle physics (i.e., without spontaneous breaking of gauge symmetry, see, e.g. Berghofer et al., 2023). I will argue that in both cases it is possible to understand the relevant invariance arguments in the established theories in terms of extrapolation from local evidence. This reveals ways in which certain theories (gauge-invariant approaches and theories that can be constructed using certain dynamical, rather than geometrical, considerations) are based on more projectable considerations than their rival theories.

20 October 2025
Nicholas Rebol (Ruhr U Bochum): Maxwell's Philosophy of Science
The 19th century saw a shift beyond the Newtonian paradigm and the mechanical view of nature. Field theories replaced mechanical interactions between matter, energy emerged as a unifying concept, and probability entered physical explanations. The work of James Clerk Maxwell on electricity/magnetism and the kinetic theory of gases was essential for this transition. From a certain perspective, given the development of statistical physics in the theory of gases and the unification of electrical and magnetic phenomena through the notion of energy and fields, it seems like the mechanistic view of nature - as merely matter in motion - was fundamentally at odds and destined to be discarded.. Nevertheless, I will argue that Maxwell's method and philosophy of science maintained an essential continuity with Newton and mechanistic physics. One can find in his work a relatively coherent and consistent integration of new field and energy concepts with a privileged place for mechanistic physics.

13 October 2025
Carina Prunkl (U Utrecht/Inria/U Oxford): How Anthropocentric is Thermodynamics?
Thermodynamics “smells more of its human origin than other branches of physics”, Bridgman famously wrote in 1941. Taking a closer look at the history of thermodynamics and statistical mechanics, we find that this ‘human smell’ enters the subject as early as the writings of Maxwell, who makes use of concepts such as ‘knowledge’, ‘observation’ and ‘the mind’ in order to explain thermodynamic phenomena. E.T. Jaynes some decades later goes even further and distinguishes between the ‘physical’ nature of energy and the ‘anthropomorphic’ nature of entropy. Both authors seem to suggest that thermodynamic concepts are in some sense mind-dependent, that they in some sense rely on the presence of an external observer. In this talk, I will revisit the question of how and when the ‘human smell’ enters thermodynamics by taking a closer look at Maxwell’s means-relative approach to thermodynamics. I will show that, in fact, Maxwell’s approach does not commit us to an anthropocentric reading of thermodynamics, but that it instead provides us with a powerful conceptual framework that carries over into classical and quantum statistical mechanics.

22 September 2025
Matěj Krátký (U Geneva): Arrows of Time in the Dappled World
Nancy Cartwright’s The Dappled World (1999) challenges the view that science delivers a unified world-picture structured by neat inter-theoretical relations. In this talk, I explore what her position implies for the debate on the origin of the arrow of time. The problem of the arrow of time begins with an explanatory demand: how can we account for the temporal asymmetries of thermodynamic phenomena, given that they are underpinned by time-reversal invariant microdynamics? Yet Cartwright denies the universal applicability of scientific laws — including those of physics — beyond their specific nomological machines. This raises the question of whether the very assumptions behind the arrow-of-time problem are compatible with her philosophy of science. I will first offer my own reconstruction of the problem of the arrow of time, and then consider how a defender of Cartwright’s position should approach it.

Convener: Manus Visser

8 September 2025
Frans van Lunteren (U Leiden): Physics as Religion
As historian Paul Forman observed decades ago, physicists throughout much of the twentieth century have cultivated an image of their field that largely ignores or even denies the material – industrial, military – contexts that enabled the field to thrive. In the many historical reflections by physicists, such dimensions are usually filtered out. A related tendency can be seen in the recurring distinction between “pure” and “applied” science, with a clear privileging of the former. To better understand this pursuit of purity, and the concomitant rejection of the material, both at the level of social context and theoretical content, it may be helpful to turn to Durkheim’s social theory of religion. This theory can also shed light on other distinctive features of the modern physics community: its drive for unification, the frequent use of quasi-religious language, and a pronounced sense of vocation. More broadly, this theory offers insight into the nature and function of academic disciplines as social institutions.

3 September 2025
Maria Papageorgiou (IQOQI Vienna): The role of dynamics in the relativistic quantum measurement problem
Recent developments in measurement theory for relativistic QFT offer new perspectives on the long-standing Measurement Problem. The strict dichotomy between measurement and dynamics is absent in relativistic theories. This is because the representation of dynamics in such theories imposes crucial constraints on relativistic quantum measurements. Sorkin's "impossible measurements" scenario, and related work, demonstrates that microcausality alone is insufficient to prevent superluminal signalling in relativistic quantum theories employing Lüders' rule. This raises fundamental questions about local operations and their interpretation in QFT. In this talk, we will examine how recently developed measurement theories, particularly detector-based approaches and the Fewster-Verch framework in algebraic QFT, address these challenges. These approaches often model measurement as a local scattering process, where the field is suitably coupled to a probe system. The causal dynamical properties of the local scattering map play a crucial role in the analysis of signalling between the probes. We investigate the dynamical assumptions required to ensure no faster-than-light signalling or retrocausality. We argue that the resolution of "impossible measurements" necessitates a departure from the traditional operational interpretation of local algebras and a re-evaluation of state update rules.

24 June 2025
Presentation of RCNP bachelor theses
Ella van Dalen: The Free Will Theorem
Lucas Timmerman: Explaining the Arrow of Time

27 May 2025
Caspar Jacobs (U Leiden): Does Quantum Gravity Happen at the Planck Scale?
The claim that at the so-called Planck scale our current physics breaks down and a new theory of quantum gravity is required is ubiquitous, but the evidence is shakier than the confidence of those assertions warrants. In this paper, I survey five arguments in favour of this claim - based on dimensional analysis, quantum black holes, generalised uncertainty principles, the nonrenormalisability of quantum gravity, and theories beyond the standard model - but find that none of them succeeds. The argument from nonrenormalisability is the most convincing, yet it requires the unwarranted assumption that the same constant of action occurs in every quantum field theory. Therefore, our theories don't (yet) predict that quantum gravity happens at the Planck scale.

20 May 2025
Sean Gryb (RU Groningen): How ignoring scale leads to a new explanation of the arrow of time
Explaining the vast time asymmetries of everyday processes using the near time-reversal invariant laws of fundamental physics is an important open problem in the philosophy of physics. Current leading proposals involve either postulating a time-asymmetric initial condition, a Past Hypothesis, or a fundamental time-asymmetric law for explaining the arrow of time. But both these proposals face stiff criticism. In this talk, I will develop a new proposal based on a symmetry argument. I will show that if one takes seriously the claim that the cosmological scale factor is not observable, in the sense that no observations in cosmology depend on it, then the dynamics of the remaining degrees of freedom take on a very different character. In particular, the scale-free dynamics display a friction-like behaviour characterised by attractors. These new features, I claim, can explain some of the most significant empirical features of the arrow of time in our Universe.

6 May 2025
Richard Dawid (U Stockholm): Final but Incomplete?
String theory has not come close to a complete formulation after half a century of intense research. On the other hand, a number of features of the theory suggest that the theory in its complete form may be a final theory. The combination of conceptual incompleteness and allusions to finality seems difficult to grasp. Two main points are made in this talk. First, it is pointed out that finality claims in the context of string theory are motivated in a fundamentally different way than traditional claims of finality one finds in earlier physics. Second, it is argued that finality and chronic conceptual incompleteness may be related to each other in a string theory context in an interesting way. The talk ends with discussing possible implications of this situation for the long-term prospects of theory building in fundamental physics.

8 April 2025
Christoph Lüthy (U Radboud): The Late Origin and Mystery of the Timeline
This lecture has two objectives. The first is historical, the second is systematic. The historical part will be about the fact that contrary to what is generally assumed, the representation of time as a straight, forward-moving, horizontal line is a recent invention which only managed to impose itself from the late 18th century onwards. Why this is so, will be explained in some detail. The systematic objective is to engage the members of the Radboud Center for Natural Philosophy in a discussion about what an adequate representation of time might look like (and whether there can be an "adequate representation" at all, and whether time is something that needs, or deserves, representation). This discussion will depart from some of Carlo Rovelli's claims about this topic.

25 March 2025
Hans Maassen (U Radboud): Copying Quantum States
The "no-cloning" principle in quantum information says that an unknown quantum state cannot be copied. A refinement of this principle has it that pure quantum states can be copied if and only if their state vectors are known to lie in an orthogonal family. A further refinement extends the principle to mixed states under the name of "no-broadcasting", and says that mixed states can be "broadcast" if and only if their density matrices are known to lie in a commuting family. In this talk we discuss these versions of the "no-cloning" principle, and provide mathematical proofs. The standard proof of the pure state version, as found, for example, in Nielsen and Chuang's textbook, by oversimplification makes it look almost trivial. It then comes as a surprise that the ingenious 1996 proof of the mixed state version by Barnum et al., which is based on fidelities, is quite complicated. In our proofs we follow Lindblad's 1999 approach, based on *-algebras of observables. Classical copying is naturally included. We give the pure states a fair treatment, which must be slightly more complicated than is usual. The mixed state case hopefully becomes more transparant. The upshot will be that a set of states can be cloned if and only if they can be distinguished by measurement, and that they can be broadcast if and only if they lie in the convex hull of such a set of distinguishable states.

11 March 2025
Henk de Regt (RCNP): Models and mechanisms: Physical understanding in the nineteenth century
In my 2017 book Understanding Scientific Understanding I have presented an account of scientific understanding that explains how criteria for scientific understanding vary with the historical and disciplinary context. In my talk today I will illustrate this account with a case study from nineteenth-century physics, in which mechanical models were seen as ideals of intelligibility. In particular, I will discuss an episode in the development of the kinetic theory of gases that centered around the so-called specific heat anomaly, focusing on a controversy between Maxwell and Boltzmann about the validity of the latter’s solution for the anomaly.

25 February 2025
Enrico Maresca (U Pisa): Fundamentality and Disappearance of Spacetime: The Case of Quantum Gravity
Numerous theories of quantum gravity postulate non-spatiotemporal structures to describe physics at or beyond the Planck energy scale. This contrasts sharply with the spatiotemporal framework provided by general relativity, which has proven successful in many low-energy scenarios. This contrast gives rise to the so-called "problem of the disappearance of spacetime:" the challenge of reconciling a fundamental non-spatiotemporal description with relevant structures in the absence of a well-defined notion of spatiotemporality. In this paper, I argue that a precise formulation of the problem presupposes the specification of the relevant conception of spacetime fundamentality. I then provide a precise definition of the problem of the disappearance of spacetime, along with expectations for its resolution. To illustrate this, I distinguish between two forms of disappearance of spacetime, corresponding to intra-theoretic and inter-theoretic fundamentality relations. I argue that intra-theoretic analyses of fundamentality can offer valuable insight into the disappearance of spacetime in quantum gravity only if supported by additional independent arguments.

28 January 2025
Martin Voggenauer (RCNP): Explaining Objective Probabilities by Physical Symmetries
In this talk, I discuss the relationship between the method of arbitrary functions and single-case probabilities, and offer an interpretation of these probabilities by reference to physical symmetries of chance experiments. The method of arbitrary functions attempts to explain outcome frequencies through the underlying deterministic dynamics of chance experiments and the constant proportions of these dynamics that lead to different outcomes in repeated chance experiments. However, the method of arbitrary functions alone appears to provide no comprehensive interpretation of deterministic chance since it relies on distributions of initial conditions that, in turn, require interpretation. In the talk, I propose an explanation of the constant proportions of dynamics via the physical symmetries of single chance experiments. By doing so, I attempt to develop the method of arbitrary functions into a comprehensive interpretation of probability that does not rely on the distribution of initial conditions and, moreover, covers genuine single-case probabilities.

14 January 2025
Joseph Berkovitz (U Toronto): On the role of intuitive thinking in scientific reasoning
The common epistemic frameworks in the literature focus on propositional knowledge and conscious inferential reasoning and portray inductive reasoning in logical terms. The idea is that, ideally, the relation between the evidence and the conclusions of an inductive inference should be logical. It is thus common to call the system of rules that should govern rational inductive reasoning ‘inductive logic’. We argue that the common epistemic frameworks largely overlook or marginalize the central role that non-propositional epistemic resources and unconscious, non-inferential reasoning play in constituting the nature of scientific reasoning and knowledge. In particular, we argue that these frameworks severely restrict the scope of incorporating the role that non-propositional epistemic resources, such as instinctive and intuitive thinking and know-how, play in scientific reasoning. Although there is no denial that such non-propositional epistemic resources help developing and applying scientific knowledge, the common view is that they do not play a role in characterizing the nature of scientific reasoning and knowledge or their justification. Inspired by our reading of David Hume’s epistemology and Bruno de Finetti’s philosophy of probability, we propose a new epistemic framework that places instinctive and intuitive thinking and know-how at centre stage. In this framework, non-inferential reasoning – which is irreducible to propositional reasoning and largely unconscious – plays a fundamental role, and the foundations of scientific reasoning are psychological rather than logical. We conclude by considering the implications of this framework for scientific reasoning and knowledge.

2024

Convener: Manus Visser

16 December 2024
Klaas Landsman (RCNP): Is mathematics a game?
We (the speaker and former mathematics and philosophy student Kirti Singh) re-examine the old question to what extent mathematics can be seen as a game. Under the spell of Wittgenstein, we answer that mathematics is a "motley of language games". The nature of these games was largely clarified by Hilbert, whose formalism--properly understood--explains both the rigour and the applicability of mathematics, so to speak via different language games both based on axiomatization. Axioms are analogous to the starting position of a game of chess, whilst logical rules of deduction resemble possible moves. Sentences are like arbitrary positions, among which theorems are the legal positions, their proofs being the counterparts of games played according to the rules. Like positions in chess, mathematical sentences cannot be true or false by themselves; true statements in mathematics are _about_ sentences, namely that they are theorems (if they are). In principle, the potential certainty of mathematics resides in proofs, but to this end, in practice these must be “surveyable". Wittgenstein and Hilbert unfortunately proposed almost oppositie criteria for surveyability; we try to overcome their difference by invoking computer-verified proofs. We do not regard this view as a philosophy of mathematics by itself, but rather as a coat rack onto which various (traditional and new) philosophies of mathematics (such as formalism, intuitionism, structuralism, and the philosophy of mathematical practice) may be attached and may even support each other.

9 December 2024
Jos Uffink (U Minnesota/Utrecht): Irreversibility in the Quantum Boltzmann Equation
I will review Boltzmann’s (1872) derivation of the Boltzmann equation in classical gas theory, and its problems. I will then discuss a more recent approach to derive a quantum Boltzmann equation in the quantum theory of condensed matter by David Snoke (2020). I will argue that the problems encountered in the quantum version of the Boltzmann equation are even worse than for its classical counterpart.

11 November 2024
Research introduction session: everyone briefly introduced the research they are currently working on or the topics they would be interested in doing research on. Students briefly presented their thesis projects.

28 October 2024
Jeremy Butterfield (U Cambridge): Emergent ontology and structural realism: quantities as objects and objects as quantities
I argue that physics' endemic practice of solving problems by defining appropriate quantities suggests a natural formulation of two philosophical doctrines, viz. (i) the claim that the objects of the special sciences (and of everyday life) are patterns, and (ii) ontic structural realism. For physics' focus on its appropriate quantities suggests treating quantities as objects: which gives a formulation of the idea of objects as patterns. And it also suggests treating objects as quantities: which gives a formulation of ontic structural realism. I develop these proposals and give some examples from physics. My discussion owes much to work by David Wallace.

24 September 2024
Silvester Borsboom (RCNP): Global gauge symmetry breaking in the Abelian Higgs mechanism
In this talk I present the work of my master thesis (see here) about the Higgs mechanism, in which I aimed to resolve the apparent contradiction between two gauge-invariant accounts of the Abelian Higgs mechanism that are widespread in the philosophical literature: the first uses global gauge symmetry breaking, and the second eliminates spontaneous symmetry breaking entirely. I attempt to reconcile these two approaches by using the constrained Hamiltonian formalism and symplectic geometry. First I demonstrate that, unlike their local counterparts, global gauge symmetries are physical, and explain how the dressing field method produces the Coulomb gauge as a preferred gauge for a gauge-invariant account of the Abelian Higgs mechanism. I then extend this analysis to quantum field theory, where the Abelian Higgs mechanism can be understood as spontaneous global U(1) symmetry breaking in the C*-algebraic sense.

9 September 2024
Annica Vieser (U Geneva): Functional reduction: implications downstream
If a concept is best understood through functional reduction (along the lines of Lewis 1970, 1972), what does that imply for a second concept that depends on the first? I sketch different ways of approaching this question on a general level in view of the kind of dependence at play. I then turn to a specific instance of dependence on a functionally reduced concept: Suppose a functionalist account of spacetime emergence in quantum gravity is correct, what does that imply for the concept of causation? I discuss different possible answers to this question, with a special focus on whether there is a route from a functionalist account of spacetime to a functionalist account of causation.

3 September 2024
Jay Armas (U Amsterdam/Copenhagen): Conversations on Quantum Gravity: a teaser
I will speak moderately loosely and freely about my book “Conversations on Quantum Gravity” published August 26th 2021 in Cambridge University Press. I will provide a kind of catalogue of ideas that people consider useful and important in a theory of quantum gravity and how those ideas relate to different approaches to quantum gravity. I will then focus on specific debates, in particular in Loop Quantum Gravity, in an attempt to highlight some of the shortcomings of given approaches to quantum gravity.

21 May 2024
Michel Janssen (U Minnesota): Constructing the Cathedral of Quantum Mechanics
I give a brief overview of the development of quantum theory from Planck's work on black-body radiation around 1900 to von Neumann's introduction of Hilbert space in 1927. This overview is based on Constructing Quantum Mechanics (Oxford, 2019/2023), a book in two volumes, co-authored with Tony Duncan, on the genesis of quantum mechanics. The subtitles of these volumes are The Scaffold: 1900–1923 and The Arch: 1923–1927. As these subtitles suggest, we see the transition from the old quantum theory of Bohr, Sommerfeld and others to the new quantum theory of Heisenberg, Schrödinger and others not as demolishing the old building and erecting a new one on its ruins but as using parts of the old building as the scaffold to build the arch of the new one.