"Epistemology of the Multiverse"

Until summer 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". 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. A systematic overview of all my thoughts and reflection on these topics will be found in my forthoming book "Multiverse Theories: A Philosophical Perspective", which will appear in 2020 with Cambridge University Press.

Philosophy of physics

I am intrigued by the challenge to make sense of quantum theory. I have recently become interested in accounts that postulate retrocausality to solve the foundational problems of quantum theory and related strategies, see here for a review article that I wrote with Pete Evans on such approaches and their motivation for the Stanford Encyclopedia of Philosophy. An excellent brief account of my earlier work on quantum theory has been writtenis by Richard Healey's in his 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.

In addition, the significance of symmetries and symmetry breaking in physics have intrigued me, 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.

General philosophy of science

Some of my work on quantum theory has a direct bearing on questions with a general relevance for 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).

Epistemology

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.

Energy, ethics, sustainability and global risks

I have recently started to work on energy, ethics, sustainability, and global risks. At my own university and at LMU Munich I give courses and talks (e.g. here) on "existential risks", i.e. risks that threaten the extinction of humanity itself. I am currently working on an article on the ethics of nuclear energy deployment (see also my "Further Interests") together with Maarten Boudry, and on an article on dynamical accounts of sustainability with Jonathan Symons.

Philosophy of Mathematics

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).

Physics

As 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.

Further Interests

You can find information about my further interests and activities here on my personal webpage.