Mathematics, referred to as the “Queen of Sciences”, celebrates its day on 12 March. Dr. Łukasz Dawidowski from the Faculty of Science and Technology at the University of Silesia in Katowice, who specialises in differential equations, teaching and science communication, will tell us about numerous mathematical festivals, as well as about epidemiological modelling, which is useful e.g. in combating coronavirus.

|Olimpia Orządała|

**International Day of Mathematics is celebrated on 12 March.** **However, this is not the only mathematical festival in our calendar.** **What are the most interesting, but also the weirdest festivals related to mathematics?**

It’s hard to say which one is the most interesting and which one is the weirdest. We definitely have the Pi Number Day, although it actually takes place on different dates.

We celebrate Pi Number Day on 14 March, because the Americans write their dates in such a way that they put the number of the month first, and the day follows it, so we obtain 3.14, i.e. the first two digits of π expansion.

A special date is for example 3 March 2015, because the decimal expansion of π number contains 14 followed by 15, although this happens once per thousand years.

We have another date related to π number – 22 July. If we divide 22 by 7, the result is approximately 3.14. Due to this, the above-mentioned date is referred to as π approximation day. Therefore, we may choose among the proposed dates.

It is also worth mentioning other strange feasts, e.g. Phi Day, which is related to the so-called golden ratio. Its decimal expansion contains the sequence of 1.6, which is why the feast is on 6 January. So Phi Day in Poland competes with Epiphany.

There is also a day connected with the Fibonacci Sequence. If we arrange the sequence 1,1,2,3,5, … appropriately, we will also obtain a nice date – 23 November.

As you can see, we have a lot of “mathematically” inspired feasts. Mathematicians like playing with digits and numbers, so they very often come up with ideas of different weird feasts.

**Another interesting feast is Square Root Day, which falls only 9 times per century.**

You only have to square the numeric value of a date, taking into account the day and month. In this way, we obtain the value of the last digit in a year – e.g. 3 March 2009, 4 April 2016, 5 May 2025. This is one of the examples of playing with numbers or dates. A mathematician wouldn’t be a mathematician, if they wouldn’t play with digits.

**Our calendar also includes Sofia Kowalewska Day, to commemorate the woman who is referred to as the “First Lady of Mathematics” or “Princess of Mathematics”…**

Indeed, Sofia Kowalewska was one of the first female mathematicians. In a way, she feminised access to mathematics. Just like Maria Skłodowska-Curie, she was the one who entered the mainstream of science, receiving two Nobel prizes.

**Some numbers and terms have their mathematical feasts, whereas others are ignored.** **Where does this come from?**

We have an infinite number of numbers, and only 365 days in a year, so no more than 365 numbers can be honoured in this way. So, which ones are distinguished? Usually the most interesting ones, for example π, because we already come across it in the primary school. This is a number that we cannot do without. If we have something round, π will naturally appear in such context.

Another one that I haven’t mentioned yet is the e number. It’s also strange, untypical, often disliked, but has its feast on 7 February.

Do we celebrate zero? I don’t think so, because nobody likes to have zero PLN in a wallet, or zero success. One, on the other hand, is so standard, clichéd, that it did not gain popularity either. Similarly to other natural numbers, prime numbers, probably because we meet them on a daily basis. We pay PLN 1, 2, 3 in a shop, we have one car, two cars, three cars…

Going back to your question, I think that the most popular feast is Pi Number Day, because π seems to be the best known, or even the most liked number. It’s different in the case of e or phi numbers. A person who is not engaged in mathematics probably hasn’t encountered these numbers, although it is worth showing them, even out of curiosity.

**Such feasts are also important from the perspective of mathematics communication…**

Mathematics is one of the fields that probably have the worst PR in the universe (*laughs*). If you offer a popular science lecture in history to the youth or adults, it will be generally acclaimed. If you propose something related to chemistry, it will be a little worse, but you can still run a cool experiment. If you say that you will tell about psychology, sociology, etc., there is also some interest. But in the case of mathematics and perhaps also physics, it is much more difficult to encourage people to come and listen.

**What is Polish mathematics currently up to?**

Last year we celebrated one hundredth anniversary of Polish mathematics. Polish Mathematical Association, established in 1919, was the first Polish scientific society. Physical, chemical and historical associations were formed later.

What do mathematicians create these days? Different things. I think that Polish scientists fit into global mathematics. It is simpler in the case of mathematics, because it’s a universal language. There are no problems, for example, for an Indian to understand an American, because we use the mathematical language, which is a language of symbols and formulas.

Also, the attention of mathematicians is now focused on what grabs the attention of the whole world – coronavirus.

**What role can mathematics play in combating the epidemic?**

One of the subfields of mathematics is the so-called biomathematics, i.e. mathematics connected with biology, with certain processes that occur in a human body, but also with certain mechanisms that can be seen in the environment. Mathematicians also handle epidemiological models.

In this case, we need initial data about the spread of a certain disease – e.g. the number of people infected, resistant to disease or prone to disease. We can use these data e.g. to describe by means of mathematical formulas how interactions between these groups may occur. It is obviously important to know the type of disease, how it spreads, whether it is, for example, a flu-type virus or coronavirus. If we know the relations between these groups, we are able to create certain models which tell us how the epidemic may progress, that is to say, spread in a certain direction and rate, what is the condition for its fading and the likelihood of getting into an outbreak of epidemic, or even pandemic.

**And the final question:** **what should we wish to contemporary mathematics and mathematicians on the occasion of their feast?**

Please wish us health, as always. You can also wish us to write a good epidemiological model related to the coronavirus spread. And it would also be great if we were liked by a majority of the society. Mathematics may not be the easiest scientific discipline, but I don’t think it’s that terrible. I think that we can tell about mathematics in such a way that everyone can listen to it, whether they like mathematics or not. You can talk about mathematics that is present in our daily lives in a popular science way. Last but not least, you can wish mathematics not to have such black PR.

**Thank you for the interview.**