Question: When did you discover what field of science you wanted to work in?

Lucien Heurtier answered on 7 Mar 2023:

Great question, as it did change for me quite a lot of times.

When I was in primary school, I wanted to become a maths teacher. Then during my time in high school I was under the impression that maths teacher were very depressed since students always thought maths are boring, so I thought I’d become a researcher in maths afterall.

At the time, I thought physics was just boring. I thought it is just chemistry, where you only need to remember stuff by heart rather than understanding, and I really didn’t see the point unless you could make gold yourself.

During the first year at the university, I was among the last students of the class in physics, and among the best in maths. But then, I had an awful maths teacher and a great physics teacher. The year after, I was in the top 5 in physics, and started being interested. But I still loved maths, and still wanted to do research with it.

A few years after I got a lecture on general relativity where the professor explained us how Einstein, by using a lot of maths, understood how gravitation was working. That was a big bang in my head: I finally understood how much maths can be hidden behind physics, and powerful maths can be when it tries to explain things like the big bang.

From that point on, I wanted to do physics, and I started working with several people on black holes and gravitation.

But then, when I applied for my PhD, I met a very nice professor, and he took me as a PhD student. But this professor was doing mostly particle physics, not so much relativity or gravitation. With him, I learned a lot about dark matter, supersymmetry, and other exciting theories of particle physics. But I was a little frustrated because all the things I had learnt about gravitation didn’t help so much for my PhD and I could not use them anymore.

Then I worked more and more on cosmology and astroparticle physics, trying to understand dark matter was produced in the early Universe. And 5 years after the end of my PhD, I discovered that very small black holes (called primordial black holes) can form in cosmology, at very early time, shortly after the big bang. I started working on primordial black holes a lot, and now it has become one of my fields of expertise, which is great, because I can now study both black holes and particle physics together.

Overall, as you see from this answer, I changed of interests and disciplines a lot throughout my career. I followed my heart, but also opportunities, which sometimes are important to take at the right moment. If I had pursued from the beginning my idea of doing gravitation, I would have obtained funding for my PhD and would have needed to stop research. And after many years I could finally find a field where I feel comfortable to do things I like and which make my career successful. What you need is motivation, and a lot of advice from your family, friends, and of course, professors.