# The man who calculates the future

Under which conditions can mathematics be used to calculate how many and which animals will live where, how viruses will spread, and how strong our economic performance will be tomorrow? Christian Aarset has developed mathematical models that allow us to calculate the future. He recently completed his doctoral thesis under the supervision of Christian Pötzsche.

“Imagine an island that is inhabited by a few animals. You wish to know how many animals will be living there next year, and the year after that, or even at an undetermined point of time in the future”, Christian Aarset sets out to explain the fundamental issue he explored in his doctoral thesis. Over the past four years he has been working at the University of Klagenfurt as a predoc scientist. This “simple” problem can be calculated by hand using relatively straightforward formulas. Nature, however, is not quite so simple: If one not only wants to pay attention to the number of animals, but also to their population distribution and their spatial spread, things become more complicated. For instance, does it make a difference to the future population if the animals live in the interior of the island or along the coasts? What is the effect of more or less food, or of a warmer or colder climate? For his PhD thesis, Christian Aarset developed a theoretical mathematical model that allows him to calculate dynamic systems of this kind. The aim was to grasp the complexity in such a way that a view into the future is ultimately possible via a mathematical crystal ball, offering plausible statements on the problem. While his work as a mathematician is theoretical, he always keeps potential applications in mind: This allows him to use his findings for the calculation of ecological and economic problems.

If mathematical methods can be used to look into the future of animal populations, can this also be applied to the spread of viruses? We ask Christian Aarset and learn that he has repeatedly tried to calculate the future of the Corona pandemic in recent months. He describes the problem he faces: “You can calculate anything on the computer, and then look out of the window and realize: The real world is quite different.” It is difficult to predict human behaviour in times like these, and all attempts to use mathematics to cope with the uncertain pandemic situation are correspondingly problematic. Thus, the simulations that have already been successfully carried out by mathematicians are of immense value, and despite the complex challenges they still produce precise results. Another problem is the lack of a precise database, as Aarset explains: “ Most calculations regarding the spread of the pandemic depend heavily on the quality of the data. If we knew precisely how many people are currently infected, we could perform more accurate calculations. However, our knowledge is extremely limited, and the mistakes that are made are all the greater.”

Christian Aarset has had his own future firmly in his sights since his days at primary school: Having always preferred to play with a calculator rather than a football, he decided at an early age that he wanted to make it as a mathematician in the academic world. He will leave Klagenfurt this summer with a completed doctorate and will go on to take up a postdoctoral position at the University of Bergen. “I was extremely lucky, even though – as a mathematician – I do not believe in luck”, he tells us. In his new position he will continue to work on similar mathematical problems: “Our focus is on how genes spread in the population of all living organisms. In other words: How many living creatures have red hair, how many have black hair? How many have wings, how many have fins? These are the problems we hope to model, and I really look forward to contributing something with my existing techniques, but I also hope to learn a lot of new things.”

Over the four years he has spent in Austria, Christian Aarset has “not only learned a lot about mathematics”. At first he found the friendliness and geniality at the Department of Mathematics somewhat baffling, but in the meantime he has become accustomed to the “Austrian closeness”. Still, there are advantages and disadvantages to everything: “We Norwegians we are better at social distancing, purely because of our cultural background”, he tells us with a smile.

### A few words with … Christian Aarset

What would you be doing now, if you had not become a scientist?

My relatives always tell me that I could have worked in a kindergarten, since I always volunteer to play with their kids… and sometimes they say I’m quite childish, too.

Do your parents have an understanding of what you are working on?

I think they understand the motivation behind my work, but the theoretical details are probably a bit too technical to discuss over the breakfast table.

What is the first thing you do when you arrive at the office in the morning?

Nothing! I’m a night owl, so I often arrive at my office around lunch, and leave at some time during the night.

Rarely, although I have been practicing. Relaxing is important, so you can work better afterward!

What makes you furious?

Nothing. I prefer staying calm and solving problems peacefully.

And what calms you down?

Walks along the Lendkanal.

Who do you regard as the greatest scientist in history, and why?

When I was young, I always admired Niels Henrik Abel (one of the few famous Norwegian mathematicians) for showing that fifth order polynomials cannot generally be solved. Showing that something is possible can be easy, but showing that something is impossible is extremely hard!

What embarrasses you?

After four years in Austria, I still tend to mix up sie/er/es!

What are you afraid of?

The heat death of the universe. On a shorter timescale, the sun’s expansion and eventual explosion presents a very real threat to all life in our solar system.

What are you looking forward to?

The smell of the ocean! Bergen is a coastal city, which means salty sea breezes and fresh fish.

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