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Interview with Joost Hulshof

2 October 2023
This is our fifth interview in the interview series of the outreach committee conducted by Raffaella Mulas.

Joost Hulshof is a Professor of Mathematics at VU Amsterdam.

Raffaella Mulas interviewed him in September 2023.

Thank you for welcoming me in this wonderful office. You know, when I still didn't know you and you were on leave, I could see from outside your office that you had photos of the Beatles everywhere and various vinyl records, including a vinyl by Demis Roussos. I thought: "I cannot wait to meet this person!". I asked someone: "How will I recognize Joost Hulshof?" and they told me: "When you'll see him, you will know it's him!". This turned out to be true. And I'm very happy to have the chance to interview you now. Can you tell me something about your life and career?

I was born in 1959 in The Hague. In high school I liked mathematics and chemistry, and in the end, I chose mathematics. I studied in Leiden, and I also did my PhD there. Then I went to Minnesota for a postdoc, and I came back to the Netherlands to do another postdoc in Delft. In 1988, I became an Assistant Professor in Leiden, and I stayed there until 2000 or something, when I moved here as a Full Professor of Analysis. Then, I told myself that I was only going to hire people who are smarter than me. I was very happy when Rob Vandervorst and Jan Bouwe van den Berg joined the department, as I have learned a lot from them!

I really like your hiring philosophy! Can you also tell me something about the very interesting objects that surround you in your office?

Well, when the department had to move from the old building to this one, it was announced that we were only allowed to bring one box with things with us, and nothing else. But I took six blackboards from the old building and convinced them to take one of them here. Now there are more. I also have many books, some neckties —my favorite one is the one with Donald Duck, and nice furniture that I bought at a recycle shop. The cabinet next to you is ancient! Oh, and I was able to put a doll outside the window of my office, but I have already shown it to you, right?

Yes! The doll is amazing.

Then this is a copy of the Declaration of Independence, which was printed in the original fashion 200 years later. You know, sometimes my wife says that at home we need to clean up a little bit, and when I don't want to throw things away, I bring them to my office.

And why do you have an open umbrella?

I bought it at the Panorama Mesdag Museum, in The Hague. Mesdag was a great Dutch painter, and Panorama Mesdag is a cylindrical painting that he realized. It's really impressive, and it's huge. You can see a copy of the painting inside the umbrella! I used the umbrella only once, and then I decided to put it up there. Then, under the umbrella there is a pillow that I had to move from our couch because we have too many pillows, and under the pillow there is a wheel. I borrowed it from the physics department, where they used it for some outreach activity. On the pillow there is also a tube that one can use to shoot paper balls, and a drumstick from the last rock concert I went to just before the Corona pandemic. The drummer threw it to the audience at the end! Then, this is a doll that my sister made, and that's a bell that I bought in France. We use it for the Mathematics Colloquium. I also have a bottle of whiskey that Bob Planqué gave me with the idea of offering it to everyone whenever we want to celebrate new results—it's good whiskey!

Very nice! I have heard that you sometimes bring a blackboard with you when you go on vacation. Is this true

Yes, that happened twice. It’s this blackboard here.

Fantastic! How do your mathematical ideas take shape?

If I'm interested in a problem, I try to tackle it using different techniques. I also talk a lot to other people, in order to get inspiration, and to see different points of view. I always try not to be afraid, which is very important, and if a problem is too hard, then I take a break and I come back to it later on, after learning new things that might be helpful. I always keep a list of problems that I would like to return to at some point.

Your research spans so many different areas of mathematics. What are you working on now?

Now I'm mainly working on a system of nonlinear reaction-(degenerate) diffusion equations which arises in population dynamics. Linearising them, we ended up with very specific linear operators, and we need to understand their spectral properties first.

I see that you are using A3-papers to write mathematics—I do this when I visit my dad, because he is an artist and he only has big sketch paper around the house. What's your motivation?

I just like to have more room for writing. Writing on A3-paper is a bit like writing on the board!

What do you like the most about the mathematics department at VU?

I like the new building, I like the common room of our department, and I like this office, which feels like a room of my house to me. I am also very happy with my colleagues. There is a friendly atmosphere here. In recent years we had a boost, as we were able to have many new appointments, and it's nice that a lot of people were hired also from abroad. I also like the fact that there is more gender diversity now at the department!

I agree with you! What advice would you give young researchers?

This is a difficult question because today, for young mathematicians, life is much harder than how it was for me. For me, it wasn't too difficult to get the positions I got. My general advice would be, create a good network of collaborators, and don't be afraid when you do research!

This is good advice! Besides mathematics and music, what makes you happy?

I enjoy having fun! I like going out with friends and socializing. And spending time with my wife makes me happy! We share the passion for music, and we do many things together.

You love Rubik's cubes as well, right? What's the most interesting one that you have? 

Yes, right! My favorite one is this one, but actually it's not a Rubik's cube. It's called Megaminx, and it has 12 faces. The Rubik's Cube came on the market when I was a student. Look, there's a little booklet here. It's in Dutch, and as you can see it had the price of 7.50 Dutch Guilders. It was written in 1981 by Jan van der Craats. Here it is written "For Joost Hulshof ", by the author!

Wow! Your office is like Mary Poppins' magic bag, where anything can appear!

Haha, yes! When I read this booklet, I got fascinated. It has some serious algebra in it, and it really made me love algebra. And for my PhD thesis, I also proved some results on the Rubik's cube.

This is amazing! Thank you so much for sharing all of this. May I also take a picture of you in your amazing office, for the article?