I have very diverse research interests. The following is a broad overview of them that gives you an impression of my main philosophical ideas and preferences.
I try to make sense of quantum theory. In this video for "University of the Netherlands", I explain why this is such a challenge and outline the types of reactions to it that have been proposed:
These days, the dominant focus on my work is on an exciting programme to solve the quantum measurement problem by ultimately understanding quantum theory as conceptually similar to classical statistical mechanics, roughly along the lines envisaged by Einstein. The first ideas are presented here. Some newer results, relating to contextuality and non-locality have appeared more recently. All that work is part of the research project "Saving Reality with Exotic Causality", funded by an NWO Vidi grant. The programme was originally inspired by the idea of postulating retrocausality to account for quantum non-locality, see here for a review article that I wrote with Pete Evans on such approaches and their motivation for the Stanford Encyclopedia of Philosophy.
The reason why I started to develop that programme a couple of years ago is that I became increasinly dissatisfied with my earlier work on quantum theory. An excellent short review of that work can be found in Richard Healey's SEP-entry "Quantum-Bayesian and Pragmatist Views of Quantum Theory", Section 5.1. My papers concerning the prospects for epistemic accounts of quantum states can be found here, here, here, here, and a paper concerning the compatibility of (so-called) non-local quantum correlations with relativity theory here. My monograph "Interpreting Quantum Theory -- A Therapeutic Approach" brings together all the different threads of my earlier work on quantum theory. It was reviewed for Erkenntnis by Florian Boge.
I have also worked on the significance of symmetries and symmetry breaking in physics, in particular how symmetries connect to questions of identity among physical states (here) and what it actually means for different types of symmetries to be spontaneously broken (here, here). I was guest editor of a special section on philosophical perspectives on particle physics after the Higgs discovery in Studies in History and Philosophy of Modern Physics, together with Dennis Lehmkuhl, see here.
I am very concerned about what the transition to a world with advanced AI systems will be like for us. I have collaborated with Maarten Boudry on the question of whether advanced AI will be shaped by natural selection, with Jonathan Symons on how academic norms can be further developed if and when AI systems become superhuman in even more respects, and I have reflected on the challenge of developing advanced AI in ways compatible with liberal democracy. Together with Jonathan Symons I have developed an argument as to why sustainability is at best of limited help as an investment criterion for safeguarding the future. Elsewhere we point out a tension between global energy justice and local democracy. Together with Maarten Boudry I have developed a new argument as to why nuclear energy use can be ethically mandated in the light of climate change. At my own university and at LMU Munich I have given courses and talks (e.g. here) on "existential risks", i.e. risks that threaten the extinction of humanity itself. Together with Emilie Aebischer I reviewed Toby Ord's book "The Precipice" on existential risks.
Between 2016 and 2019 I was working on a research project "Epistemology of the Multiverse", funded by the Netherlands Organization for Scientific Research (NWO) through a Veni grant. The project explored the prospects for empirically testing theories according to which the laws of nature and the constants vary across space-time or even across universes that together form a "multiverse." A systematic overview of my thoughts and reflections on these topics can be found in my book "Multiverse Theories: A Philosophical Perspective", see here for an associated blog post. Easily accessible introductions to the themes of the projects can be found here and here. Often a "fine-tuning" for life of the laws and constants of nature is claimed to provide evidence that we live in a multiverse. I give an overview of that debate in my article on "Fine-tuning" for the Stanford Encyclopedia of Philosophy. Together with Sylvia Wenmackers I have recently applied some of the lessons of those discussions in a call for humility regarding the future of life in our universe.
Some of my work on quantum theory has a direct bearing on questions with a general relevance to philosophy of science, in particular concerning the nature of objective probabiliy and causation (here). Together with Koray Karaca and theoretical physicist Robert Harlander I wrote a paper on the notion "ad hoc hypothesis" and its application to methodological issues concerning the Higgs mechanism, in particular the violation of "naturalness" (here).
My work in epistemology focuses on problems of rational self-locating belief, a topic that has a bearing on diverse issues, from everyday contexts to the evaluation of cosmological theories. Two papers of mine in this field (here and here) explore the relevance of an epistemic agent's causal context and the appearance of anomalous causal powers according to some suggested accounts of self-locating belief.
To understand mathematics and mathematical activity, it is crucial to have a clear view of the functioning of mathematical language. I am tempted by Wittgenstein's idea that mathematical language has an essentially normative, rather than descriptive, mode of use. Whereas Wittgenstein applied this perspective on mathematics predominantly with an eye on applications of mathematics, I argue that it fits surprisingly well with the modern axiomatic approach to pure mathematics (here). As I see it, such a Wittgensteinian approach to mathematical language supports deflationary perspectives on mathematical truth and mathematical objects (in German). Inasmuch as a structuralist view of mathematical objects is compatible with such perspectives, I think that it can and should be extended to meta-mathematics (here).
When I was a PhD student in physics I co-authored three papers on high-temperature superconductivity and its relation to anti-ferromagnetism in a simple model of fermions on a lattice, the so-called Hubbard model (see here for the final installment of the series). This work is based on a renormalization group approach to the development of which my physics PhD supervisor Christof Wetterich made decisive contributions.