"Bonn is a cycling city," says the mathematician calmly. Something like that can't shock her. But she takes great care of the borrowed bike, chaining it extra-securely to a pole with a massive lock. A community, a personal network that steps in when things aren't going so well is one of the things the Cologne native particularly appreciates. "That is actually more of a characteristic of many African societies," says Hoffmann.

She has been to Ghana, Kenya, Ethiopia, Rwanda, Cameroon, Benin, Tanzania and Togo countless times to teach in workshops, summer schools and at universities what she herself has in abundance: enthusiasm for mathematics.

She also got something in return: a new world view. "I learned that I had a very selective image of Africa," Hoffmann says. This was mainly shaped by the stories that make it into the news here - for example about disasters, famine and Ebola. You hardly ever hear about the many good things about Africa in this country.

Of course there are, but: "You don't read or hear so much about the positive things," she says. For her, these include the welcome culture she often experiences on the continent, a different understanding of society in which the community plays a greater role, and that appreciating a person is less tied to their job and income. The latter makes a big difference in Germany.

Franca Hoffmann is 31 years old, eleven of which she has spent abroad. Since September 2020, she has held a junior professorship at the Hausdorff Centre for Mathematics at the University of Bonn. There she researches, teaches, organises conferences and supervises students and doctoral candidates.

In the evenings she likes to dance salsa, and she doesn't usually immediately talk about what she does for a living. Because the responses are often the same: "Really?" "I never liked maths," or "I’d never have guessed."

And when she then raves about her favourite mathematical topic, which has fascinated her since her studies at the elite university École Normale Supérieure de Lyon, the layperson is quickly lost. But she explains it anyway: she is particularly fond of partial differential equations. One of the things they can be used for is to calculate under which variable circumstances (air pressure, solar radiation) certain variables (wind speeds, temperatures) will change in the future at different locations.

That's what fascinates her about her profession: "Being able to express complicated things in a compact formula, that's the inner beauty of the world." Although she admits that as a mathematician she is stuck with a problem about 90 percent of the time without being able to solve it. "Then when you've done it, it's all the more beautiful."

Hoffmann became a sought-after mediator between various disciplines early on in her career. As the only woman in her year at Lyon ("Wasn't a problem," she says) and with a Master's degree from Imperial College London, she went to the University of Cambridge for her PhD.

First she helped a colleague with a maths problem - then she helped a whole lot of colleagues.In the UK, a PhD is usually designed to take three years. "But I wanted four, just to be able to do more," she says. And that's what she did, starting many collaborations with other subjects - at first quite by chance. While she was working on her doctoral thesis, an email from a materials scientist landed in her inbox. He had been trying in vain for months to find help with a mathematical problem for the development of battery cells.

He had written to countless of Hoffmann's colleagues, but no one replied - except the PhD student from Germany. "It turned out that the solution was not that difficult, so I helped him turn the problem into the right equation," she says.

Word of her talent as a go-between spread to other departments. She received more and more emails with questions and used her friendships from the "social networks" to find and bring together colleagues from different disciplines.

The openness with which she goes through life also got her her first trip to Ghana. At the beginning of her studies in London, she had made it onto the website of Imperial College, where she gave prospective students an insight into everyday life at the university.

At the same time, a Ghanaian NGO was looking for cooperation partners from Europe to help with maths camps for young people in Africa. The organisers came across Hoffmann via the university's website and wrote to her: "Would you like to teach some maths in Ghana?" Yes, she would like. A few emails and months later, the then 20-year-old flew to Ghana for her first visit.

Since then, work on the African continent has simply been added to Hoffmann's changing main jobs, even when she moved to the California Institute of Technology in the USA (known to fans of the series "Bing Bang Theory" as "Caltech") as a postdoc for three years.

While there, she was offered a chair in Rwanda: she now looks after it with a 20 percent position in addition to her full-time job in Bonn. As a sideline, she is also working on expanding research structures in Africa and is coordinating the establishment of a doctoral school in data science at the "African Institute for Mathematical Sciences" in Rwanda.

Hoffmann came from California to Bonn in the middle of the pandemic. There was no way she could go out and get around. The Old Customs House with its view of the Rhine helped her at least a little to get a feeling for her new city. She especially enjoys being able to do everything here by bike. "It's very different from the US, where many cities are car-centric. It’s really difficult there," she says.

For the next six months or so, she can cycle about as much as she wants. Then, at the end of the year, she’ll be heading back to Caltech in California. Besides a seven-year contract with the prospect of a permanent professorship, what particularly appeals to her there is that "it's a small institute where the work is very interdisciplinary," she says.

She wants to keep in touch with Bonn University and the Hausdorff Centre. Thanks to her distinct talent for networking, that seems to be a realistic goal.

Original text: Margit Warken-Dieke

Translation: Jean Lennox