I was interviewed by Pieter Thyssen for a publication of the Institute of Philosophy (HIW) at KU Leuven, where I started working in October 2014 as an assistant professor (TT) in Philosophy of Science.

A longer version of this interview appeared in Dutch in a publication of the Institute of Philosophy (HIW) at KU Leuven. (Also on my blog: part 1, part 2, part 3.) I translated and slightly shortened the Dutch text to this version. A slightly edited version appeared in the 2014-2015 edition of the alumni newsletter of the HIW (pp. 10 – 14).


Good morning Sylvia. While many students nowadays choose for law, industrial engineering or commercial sciences, you opted for physics. What attracted you to this discipline?

Good morning Pieter. Well, my original plan was to become an astrophysicist and to start writing science fiction afterwards. I was about fifteen years old when I thought this up, so it was just a naïve idea. Still, in secondary school it motivated me to choose consistently for the program with the highest number of mathematics classes, even though the language courses required less effort. The whole plan was inspired by Isaac Asimov, my favorite science fiction writer at the time. I knew that he was a scientist and that, besides fiction, he also wrote popularizing books, for instance on astrophysics. Ironically, I discovered only much later that Asimov himself was not a physicist, but a chemist. (Laughs)

Were you already interested in philosophy at that time?

Yes, most certainly! Besides science fiction and popularizing books on science, I also read philosophy. In particular, I remember from that period Sartre’s “Les jeux sont faits” (for French class) and Kant’s Kritik (a Dutch translation, parts of which I read during an episode of severe tooth ache, while I was continuously walking around the table). I did not understand all of it, but it fascinated me. The big questions of philosophy attracted me, but I had the impression that science was in a better position to actually answer at least part of those questions. Probably I even believed that a theory of everything – already sought after by the Greek natural philosophers – was now within reach in physics. (Sighs) Still, I realized that there remained many exciting open questions, in cosmology for instance, a field in which physics and philosophy remain equally relevant.

In any case, when I chose to study physics, I did so in the hope of studying philosophy afterwards. To me, it only seemed feasible in that order: physics first, while the preparatory mathematics was still ready knowledge. Although the physics program has a high number of contact hours and a heavy study load, I did try to keep reading on other topics. Someone told me that, if I was so interested in philosophy, I should read Wittgenstein. According to him, this would end my interest. That was a strange claim, so out of curiosity I started reading Wittgenstein: first the Tractatus, then the investigations, and then his remarks on the foundations of mathematics. I wasn’t ‘cured’ at all.

In the second year of physics, philosophy of science was an elective subject. I was the only one that year to select it. It was taught by Werner Callebaut, a Belgian philosopher of biology, who has meanwhile passed away. During my last year of physics, I wrote a thesis on the interpretations of quantum mechanics.

What was the topic of your first Ph.D. research in physics?

It was a topic in material physics. The goal of the project was to develop biosensors based on synthetic diamond. Let me say first that I landed up in this line of research more or less by accident. Actually, I wanted to start an advanced master in philosophy of science in Ghent. I had already done an entrance exam for this program. However, my father thought it was time I should earn my own income and he showed me a vacancy in the newspaper for an assistantship in physics. I had some idea of the teaching duties, but the lab research did not appeal to me – a dreamy theoretician – very much. Fortunately, optical techniques played an important role in the research and it turned out that I had a knack for that: I spent many hours at the confocal fluorescence microscope, often cursing because the protocol once again had not worked as hoped. Still, I wouldn’t have wanted to miss them for the world. When I had graduated I did not feel like a real physicist, but by the time I finished my Ph.D. project I did.

Why did you start a second Ph.D. project in philosophy? Did your background as a physicist help you in this philosophical adventure?

Well, during my first Ph.D., I discovered that I really enjoy doing research, just not on this topic. In spite of this, my career in physics did go well at that moment: I held a postdoctoral mandate of the FWO and I had positive perspectives for afterwards. Unfortunately, it is difficult to reorient your research gradually. In the end, I realized that I would have to make a clean break if I ever wanted to start doing foundational research.

I took a week of holidays to attend a conference on philosophy of science. In that way, I wanted to test out my ideals before resigning from my postdoc position. Somewhere along the road, I must have acquired an empirical reflex. (Laughs)

Whereas only few of my former colleagues in the lab are interested in philosophy, most analytical philosophers do hold physicists in high esteem. Many well-known philosophers have a background in mathematics or the natural sciences. For instance, one of the speakers on the conference that I attended was John Norton; he is a chemist by training. After the conference, a switchover to philosophy of science did not only seem feasible, I was also more enthusiastic about it than ever before.

In 2011, you defended your dissertation in philosophy on the foundations of probability theory. Can you briefly tell us something about this research?

My dissertation was a collection of articles that I wrote in the course of one year. The result of which I am the most proud is related to a fair lottery on natural numbers. Classical probability theory does not have any probability distribution for this situation. This is due to the additivity property that the theory assumes. My idea was to assign infinitesimal probabilities to the individual tickets. This is a solution that is intuitively appealing to many people, but which leads to technical complications with infinite sums of infinitely small numbers. I have been stuck for weeks on a crucial step in the proof and I remember very clearly the moment at which I saw the solution. It was a personal victory. The sort of satisfaction that you can only achieve when you work on a research project out of pure curiosity, detached of any strategic considerations or questions concerning applicability. Exactly that what I had missed before.

Besides this result, there is a chapter in the dissertation about the lottery paradox of Kyburg: that is a problem from formal epistemology; but there is also a chapter with computer simulations about yet another question on epistemology.

Which themes are you researching now? Which topics do you hope to address later on?

Currently, I work on topics from the philosophy of physics in which questions concerning small probabilities and determinism play a large role. Newtonian mechanics is often presented as the textbook case of a deterministic theory. Yet, Poisson and, more recently, Norton have drawn attention to indeterministic systems within Newtonian mechanics. Moreover, in these cases it is not clear what the probabilities are that correspond to the different solutions. I model these situations using difference equations and infinitesimal time steps. In this way, I can assign probabilities to the various solutions. The infinitesimal probabilities that I worked on during my second Ph.D. are very helpful for this purpose, too. Since it turns out to be possible to give both a deterministic and an indeterministic description of the same system, the question arises whether it is ever possible to say of reality itself that it is deterministic or indeterminstic. Or is this distinction not applicable to reality and, if so, how should we understand this?

In statistical physics, there are a number of thorny issues involving small probabilities that I would like to address in the next years. Of course, I hope to return to the foundational questions of quantum mechanics, too. It has been over ten years since I wrote a thesis on that topic and meanwhile I have required many relevant insights. In addition, there have been new experiments that can shed new light on some of the old conundrums, but that is what your research is about, too, so I don’t have to explain this to you.

In October 2014, you were appointed as BOF-ZAP research professor (tenure track) at the Institute of Philosophy (HIW) of KU Leuven. Why did you choose to start working in Leuven?

Previously, I worked as a postdoc at the department of Theoretic Philosophy in Groningen (The Netherlands). Although I did like to work there as well, after years of short-term contracts, I was craving for the prospect of a permanent position. An important benefit of the BOF-ZAP system in Leuven is that it offers a good protection of the research time: I like to teach, but I only have to organize two courses per year, such that my research does not suffer from it. In addition, the Centre for Logic and Analytic Philosophy at the Institute is currently undergoing a period of expansion and rejuvenation. It has many advantages to belong to such a dynamic center: for instance, there is at least one lecture by an internal or external speaker each week. Of course, it is nice to help giving a boost to philosophy of science in Leuven.

What are your dreams or goals as a young professor? Would you like to start a research group? Are there certain courses you would like to teach?

I have more research projects in my head than I can execute myself, so I would like to build a group, indeed. With the help of a Starting Grant of KU Leuven, I could start looking for a first Ph.D. student right away and this allowed me to hire you. It is very inspiring to work in a team and, fortunately, our current center offers a good context for this. I am already teaching philosophy of science to Master students of Philosophy. Besides this, there is our reading group on the philosophy of quantum mechanics. I would like to continue these during the next years. For the near future, I hope to be teaching philosophy on the science campus. Confusing these students with questions like ‘What is a number?’ or ‘Do electrons really exist?’, now that would allow me to flourish.

Many scientists are skeptical towards research in philosophy of science. What is the reason for this according to you? And do you as a young professor hope to change this?

To an extent, I do understand this attitude and, on the one hand, it is fine that not all scientists want to lose themselves in philosophical thinking: otherwise, they would no longer manage to make progress with their own work. On the other hand, it just goes to show that science, not only by scientists, is regarded as indubitable too easily. Ironically, this attitude is itself a philosophy.

You blog regularly on your own website and you also write for EOS magazine. You are also active on Twitter. Why do you find it important to communicate with a wider audience?

Popularizing books played a key role in my own choice for science and philosophy. I think it is now my turn to pass on some of my knowledge and experiences in this way: to pay it forward. Although I publish about my research almost exclusively in English, I write my blog posts in Dutch. This is a deliberate choice: I want to open up a part of the information that is already available online to people – young or old – who are not comfortable with searching in English sources. Of course, I also simply enjoy talking about my research. On my blog, I can do just that without having to hold back out of fear of boring someone: only those who are actively looking may stumble upon it.

Science and philosophy are clearly two major passions for you. Do you have any other hobbies? For instance, I heard from a reliable source that you are interested in art, travels, graffiti, nature, games, (street) theater, and even dragons (!).

I have long aimed for the ideal of the universal human, so I have spent quite some time in the drawing academy. I hope to find more time for that once, but I notice that drawing has changed permanently my way of looking. Whether it’s the clouds, a tiny insect, or an imaginative theater costume: I always look at it in a searching manner, with at the back of my mind the question of how I could draw it. Due to lack of time, I currently have to stick to taking pictures – for instance on the topics on the list – and blogging. My interest in dragons is related to my collection of fairy tales. Since I have been to China, I am also fascinated by the more positive role that dragons play in Eastern stories. My son was born in the Chinese year of the dragon, so drawing the illustration for the birth announcement card came easy.

As a final question, suppose you could hold a dinner with four people of all times (scientists, philosophers, artists …). Who would you invite and why?

My initial idea was to invite Leibniz and Newton, because they never spoke in reality. However, because of their well-known dispute on who invented the calculus, it probably would not lead to a pleasant conversation. In fact, I doubt that Newton would accept the invitation at all. Hence, I place all my hope in Leibniz. Can I invite four copies of Leibniz? Then I can talk with the first copy about his infinitesimal calculus, with the second one about probability and jurisdiction, with the third about his Sokal hoax avant la lettre in alchemy, and with the fourth about our ongoing fascination with reckoners (computers).

No, we have to be strict: that is not possible.

Okay, then I would send the second invitation to the eighteenth century Émilie du Chatelet to converse about determinism and the mechanics of Newton and her criticism of Locke. My third invitee would be Leonardo Da Vinci, because of his affinity with both science and art. Since he invented an adding machine, I foresee an animated conversation with Leibniz as well. The fourth invitation goes to Anne Tyng. She was an American achitect who died in 2011. She was greatly inspired by Platonic solids and other geometric forms. She was a professor in morphology at the University of Pennsylvania. For instance, she designed a house for her parents, which was based on an unusual cross section of a tetrahedron. I discovered her work by accident after such a partition of the tetrahedron had emerged in one of my computer simulations.

Well, if you continue your work on your project on time travel, then maybe you can tell me if it would be possible in principle to organize this dinner.

I will keep you informed! Thank you for the interview.

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