Colloquium

The biweekly RCNP colloquium usually takes place on Tuesdays at 15:30 and comprises talks by invited speakers as well as RCNP members. For questions, please contact Manus Visser.

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

Schedule

3 June 2025
Frans van Lunteren (Leiden): t.b.a.
t.b.a.

27 May 2025
Caspar Jacobs (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 (Groningen): t.b.a.
t.b.a.

6 May 2025
Richard Dawid (Stockholm): t.b.a.
t.b.a.

8 April 2025
Christoph Lüthy (Radboud): t.b.a.
t.b.a.

25 March 2025
Hans Maassen (Radboud): t.b.a.
t.b.a.

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.

Past speakers

25 February 2025
Enrico Maresca (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 (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.

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 (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.

28 October 2024
Jeremy Butterfield (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 (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 (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 (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.