# In conversation with Matt Parker

Matt Parker is a nerd, and proud of it. So nerdy that, in a list of the nerdiest things he’s ever done, hiking for three days through the Australian outback to document a ‘confluence point’—an integer intersection of a line of latitude and a line of longitude— “might not even make the top ten”. A quick scroll through his YouTube channel (standupmaths) shows videos with titles like Back to the fax machine, Speed Rubik’s cubing for drunk people and Stand-up comedy about equations that correspond to vortex motion. In the latter, he makes jokes about integration and pokes fun at physicists for calling a torus a doughnut. The video also has over 300,000 views, so clearly there is a huge audience for his brand of nerdiness. When we met Matt, on a grey evening in late January, he was about to embark on a week of talks around the country where he would share his enthusiasm for maths at festivals and in schools. “I want people to learn stuff, sure, but I’m also trying to do a bit of maths PR. I want to make the nerdy kids cool for the day.”

## An unexpected journey

Although Matt has a clear mission now, he admits this wasn’t always the case. “Basically, I didn’t have a career plan. I’d done a bit of tutoring at university and loved that, so I got my teaching qualification and moved to the UK.” He had always been interested in making videos and writing comedy, and while working as a teacher he realised he was missing that creative outlet. So, the stand-up mathematician was born. At first, his comedy routine played off the fact that he was a mathematician “who expects life to be logical.” Being a teacher also helped: “When you say you’re a maths teacher then, for better or for worse, people have an image of that. And you can play with it.” Gradually the comedy became nerdier, he started being more involved with university engagement programmes, and eventually in 2012 he left teaching and made the transition to being a full-time outreach mathematician.

Matt grew up in Australia, which famously celebrates Christmas at the wrong time of year.

These days, Matt gives talks to nerds and non-nerds alike. “If I can make a room full of nerds laugh at a joke about spreadsheets, that’s great. But in some sense, that’s the audience.” Working with kids, on the other hand, is much more challenging and requires careful judgement. “The moment they think you’re trying to impress them, it’s all over.” You have to pick your jokes wisely, and make sure that the educational content still comes through. If it works though, and you can get teenagers who don’t want to be there accidentally enjoying themselves while they learn about mathematics, then it’s a “much bigger achievement.”

It is really important for maths outreach people to keep in touch with teachers…to check what we’re doing is useful.

It’s clear that Matt’s time in teaching has had an effect on the work he does today. His goal is to keep his sessions relevant to what teachers are doing at school, and make them a part of the experience, which “keeps the excitement going” once the day is over. “I don’t want to do shock and awe mathematics, where they go back to the classroom and say, why aren’t our lessons like that guy’s?” This is also the reason that he started MathsJam, the monthly meet-up series that brings together mathematicians of all stripes in pubs around the world. “It is really important for maths outreach people to keep in touch with teachers, to find out what they need and whether what we’re doing is useful.” It’s a great approach to outreach: something that fits within the system and complements the everyday job of educators, rather than creating a division between ‘fun maths’ and ‘school maths’.

In recent years, a lot of Matt’s most well-known output has been through YouTube videos, either from his own account or as a guest on the mathematics channel Numberphile. Here again we find him carefully balancing his different audiences. “I would be disappointed if my videos were only watched by maths people, but likewise I would be disappointed if I don’t occasionally put out videos for that demographic.” Sometimes Matt can tell that a topic is going to provoke interest among non-mathematicians. One example of this is a video with Hannah Fry titled The mathematics of winning Monopoly, where they crunch the numbers to work out which squares are worth buying. At other times, the internet doesn’t react the way you would expect and a video that took a lot of effort to produce barely makes a splash.

So some videos land well and others don’t, but being mathematicians we felt the best way to understand Matt’s career as a YouTuber was to take an average. Specifically, to watch his median video, according to quality. “I made a video once about ordinal and cardinal numbers. And it was fine. Just, fine.” Cardinal numbers are used to count how many of something there are (you can have zero apples, one orange, three pineapples, etc) and ordinal numbers order items into first, second, third. Matt wanted the video finished in time so that he could show it at a talk, where he would test his audience’s powers of self-organisation. Everybody who came to the talk was given a slip of paper with a number written on, and the challenge was for them to comment on the video online in the correct order. “It got to over a hundred, before I released the video to the public and they broke it.”

“Cardinal numbers are so-called because they are holy. As in, they are whole numbers.”

Over the course of more than one hundred videos, Matt’s YouTube channel has covered all sorts of mathematical and mathematically-related topics in an entertaining, accessible way. But there are some topics that he won’t ever make a video on. The Riemann hypothesis is a classic example of a popular, famous topic that he feels just won’t work on YouTube. “First of all, you’re going to have to do plotting a complex function… and the Basel problem, and what the zeta function is generalising. Suddenly you realise there’s so much background stuff, that a video is just not the right format.” This desire to tell a story all the way through is what led to Matt’s first book: Things to Make and Do in the Fourth Dimension, which was published in 2014. Although the book deals with lots of different mathematical topics, ranging from knots to different size infinities, Matt was “setting up everything he needed to do the Riemann hypothesis properly.”

## Making mistakes

Image: Penguin books

Matt’s new book, released in March 2019, is called Humble Pi. The book is framed as a collection of errors in mathematics: times when people made a mistake and faced real-world consequences. But actually, Matt says, the real aim was to show people how maths is “incredibly useful and underpins society.” By telling stories and anecdotes about these mistakes, he hopes to reach people who “wouldn’t normally pick up a maths book” and show them that maths is everywhere… just you might only notice it when it goes wrong.

The stories contained in the book range from the serious to the sublime. For example, in 1997 the cruiser USS Yorktown was left powerless during training manoeuvres after a crew member tried to divide by zero and crashed all the computer systems that controlled the engines. Another chapter tells of a flight in Canada that had to make an emergency landing after ground crew twice used the wrong amount of fuel. Their mistake? To calculate the amount needed in kilograms, and then load the tank with that many pounds. But Matt was cautious not to fill the book with disaster tales. “Nobody dies in any of the [aviation] stories. It’s safe to read if you’re scared of flying.” Some of them—like the tale of Steve Null, whose unfortunate name was incompatible with the company database—are just there to tickle you.

“A metaphor for something that is almost right, but a little off.”

And yes, the book does include a mistake that Matt himself has made. The ‘Parker square‘ is an attempt at making a 3-by-3 magic square using only square numbers. He suspected that his methods weren’t perfect, but he thought it would be fun so he gave it a go. And, lo and behold, his answer included a mistake (check the diagonal sums in the image on the right). Matt uses the Parker square to teach us another important lesson: mathematics is often about making mistakes. “Mathematicians are not people who find maths easy, they’re people who enjoy that it’s difficult… we make mistakes all the time. People wear T-shirts that confirm this.”

Another part of Matt’s life these days is that he regularly signs calculators. What began as a light-hearted joke now sees hundreds of school children around the country with their names Sharpie-d in the encoding standard Ascii on their devices. Matt takes great pleasure in doing this; not only is it an ironic celebration of nerdiness, and gives the students some maths to do if they want to read his message, it serves as a reminder of their experience that will last for months or years afterwards. “If they get so involved that they want to get their calculators signed, then I think that’s hilarious.”

As a mathematician and comedian, Matt seems to be in the middle of two very different worlds. But he’s happy there, describing it as a “stable equilibrium”. He has many outlets for his creative side, and says that he could “probably find something else to scratch that itch if he wasn’t doing comedy.” But as for maths, there’s nothing that can replace it. “It’s much more pervasive in your life. It’s something that you’re always thinking about.” Even when you make mistakes, “it’s worth putting the effort in, because when you get it right it’s just so useful. And so fun.”

Would you like to win a signed copy of Humble Pi? Tell us about a time when you’ve made a mistake in mathematics by sending us an email before 9 September 2019, and Matt will pick a winner!

# In conversation with Eugenia Cheng

We meet Eugenia Cheng a couple of hours before she’s scheduled to give a talk at City University, where she’ll make another stop on her journey to “make abstract mathematics palatable” in the public consciousness. With over 10 million views on YouTube, three best-selling books in How to Bake Pi (2015), Beyond Infinity (2016) and The Art of Logic in an Illogical World (2018), and interviews ranging from the BBC to late night US television, it’s safe to say Cheng has made incredible progress on her mission.

## Not ‘just’ a mathematician

In talking to Cheng, you quickly realise that she is always trying new activities, pursuing further study and pushing herself to understand more of the world around her. She read voraciously growing up, but describes mathematics as “the only subject to stand up to [her] desire for rigour”. In attempting to satisfy her “curiosity for asking why things are true”, Cheng learned of category theory, the study of relationships between similar themes and concepts in different branches of mathematics. She describes this field as particularly abstract, but remarks that it could be viewed as a prerequisite to most undergraduate courses in the way it identifies links in areas of mathematical study. In her view, category theory does for mathematics what mathematics does for the world. This concept takes a little bit of mental gymnastics, and Cheng takes it a step further in her current research in higher-dimensional category theory. She studies the relationships between the relationships themselves, adding  “an extra layer of subtlety” to her understanding of mathematics.

Mille-feuille is a type of pastry made with hundreds of layers. Image: Eugenia Cheng

It’s clear that Cheng’s research has influenced the way she approaches her other passions, which include food, music, and teaching. An avid baker, Cheng’s first book, How to Bake Pi, begins each chapter with a recipe for the reader to try. This method mirrors the conversations that introduce chapters in Douglas Hofstadter’s seminal work Gödel, Escher, Bach: An Eternal Golden Braid, which she credits as a “very influential book” for her approach to writing about mathematics. Cheng believes that the general public is suffering from a severe case of “maths phobia”, and that introducing mathematics in recognisable, accessible ways is far more effective than teaching times tables and long division. On her appearance on The Late Show with Stephen Colbert in 2015, Cheng introduced the concepts of exponentials through making mille-feuille live with the host. Children as young as seven have, through How to Bake Pi, gained an understanding of complicated abstract mathematics, and she recounts a story of a five-year-old calling out to her “I’m your biggest fan!” at one of her outreach talks. By giving younger and younger children an appreciation of what mathematics can do and how it is expressed in the world around us, Cheng believes that the fear of mathematics so many schoolchildren feel will erode and disappear over time.

Cheng modelling the new Chalkdust T-shirt

Cheng is the founder of the Liederstube, an environment for classical musicians to come together and enjoy performances in a relaxed setting, based in the Fine Arts building in Chicago. A talented pianist, Cheng performs alongside her busy schedule writing books and giving talks. When asked about whether performing in concert halls is more nerve-wracking than giving talks at the Royal Institution, Cheng doesn’t hesitate: “Compared with playing the piano, public speaking is easy! You can say whatever you want, and you don’t have to say particular things in a particular order.”

Cheng was a featured speaker at Stem-con 2017. COD Newsroom, CC BY 2.0

As the scientist in residence at the Art Institute of Chicago, Cheng teaches abstract mathematics to undergraduate art majors. She enjoys teaching mathematical ways of thinking to socially conscious students, giving them the ability to “frame social issues in a mathematical sense”. Perhaps these students represent the ultimate cases of maths phobia, but according to Cheng, there is a lot more in common between those that study mathematics and the students she sees weekly. Through her courses, Cheng is learning as much from her students as the other way around. She had not realised the applications of mathematical thinking as a “framework to agreeing on the world, something badly needed in today’s public discourse”. The parallels between Cheng’s passions and her research are immediately apparent. She finds the mathematical similarities between music, food, and teaching in the same way she identifies connections between areas of mathematics in category theory.

## Women in mathematics

Eugenia Cheng is a role model for many young women interested in maths. COD Newsroom, CC BY 2.0

As a prominent woman in mathematics, especially in popular culture, the question of the gender gap inevitably came up. By Cheng’s own admission, she “was initially reluctant to address the issue” at the beginning of her career. A firm believer in the meritocracy of academia, she is certain she’s “able to achieve anything a man could in mathematics”. Cheng says that “when women in academia are young and not treated with much respect, they think it’s because they are young and junior. But as they progress, they continue to notice the lack of respect, making it clearly a feminist issue.” Cheng has also realised how important it is to act as a role model, and has embraced the challenge of becoming more visible to young women in mathematics. For Cheng, the most important message to communicate to these students is that “they are good enough”. Students that are struggling are “not finding it difficult because they don’t understand. They are seeking a deeper level of understanding-exactly the kind of person needed in higher level mathematics.” Cheng sees a marked difference in how the average female student approaches applying to PhD courses compared to their male counterparts. She admits that if she had not been offered the opportunity to study for her doctorate at her first choice (Cambridge), she would have given up pursuing a career in higher level mathematics, taking the rejection as a comment on her ability. She believes that in applying for mathematical postgraduate positions, women have to take the same persistent approach that men do, applying for any opportunity that allows them to follow their passions.

Cheng also feels that too much self-confidence in one’s own abilities doesn’t make the best students. “Most people think that self-confidence is the most important part of being a mathematician, whereas I believe that self-criticism is far more important. I’d much rather work with a student that underestimated their own abilities, than the other way around.

Most people think that self-confidence is the most important part of being a mathematician… I believe that self-criticism is far more important.

In fact, Cheng believes there needs to be a reframing of the whole argument, proposing new words to replace masculine and feminine, as “we shouldn’t prescribe behaviours to genders”. For masculine, Cheng suggests ingressive’. “Ingressive-it’s all about getting the right answer, being competitive, being first, exactly the way we teach mathematics at a young age.” Even the way we test is ingressive: “Exams are an ingressive thing too,” Cheng says. “You have to get as much done as you can, as right as you can, as quick as you can.” But research isn’t like that at all. “Research is congressive,” Cheng explains, using her replacement word for feminine. “You’re trying to discover deeper insight, you have to work collaboratively. It takes time and it takes patience.” And therein lies the problem, according to Cheng. “We’re selecting ingressively for a subject that should be very congressive in nature,” she concludes. “I suspect we’re losing a lot of talent this way.

## The art of logic

Cheng’s new book tells us how mathematical thinking can be applied to questions about social issues such as LGBT rights

Just before Cheng has to nip off for her talk, we move onto the subject of her new book, The Art of Logic in an Illogical World. “This really grew out of teaching art students because the ones I teach are so socially conscious, and want to change the world,” Cheng says. “It was a bit like when I used baking to perk up my mathematics undergraduates. If I talked about a social issue from a mathematical point of view, then they were all completely alert.” The book is a summary on the “insights mathematical thinking gives me on social and political issues.” In summary, the book is about “the nature of disagreement.”

Mathematics is a way of being clear and unambiguous, and we need that today.

We later attend one of Cheng’s talks at the Royal Institution, based on her book, and it’s fascinating to see how mathematical thinking could be applied to questions of LGBT rights, racial privilege and political disagreement. “I always read the comments below news articles,” Cheng said, prompting a sympathetic laugh from the audience, “You have to! You have to know how people see the world so you know how to talk to them.” Cheng’s belief that mathematical principles allow us to cut through overly complicated debate is infectious and so clear, you wonder how anyone could possibly disagree.

“Mathematics is a way of being clear and unambiguous, and we need that today,” Cheng concludes. Through her writing, talks and outreach work, there’s no debating the important work she’s doing for the subject, curing cases of maths phobia every day.

# In conversation with Chris Budd

“Let’s chat any time, I’m fairly free.” Coming from Chris Budd, a professor of mathematics at both the University of Bath and the Royal Institution, as well as a board member of several of the most influential mathematics organisations in the UK, this is somewhat of a surprise. But he is true to his word, and one Friday afternoon we sat down for a conversation with one of the UK’s most experienced voices in mathematics communication.

The University of Bath. Wikimedia commons, CC BY-SA 3.0

A quick glance at Budd’s website reveals, through a CV that runs to 25 pages, the diversity of his interests and professional experiences. At various times, he has advised on setting A-level examinations, held high-ranking positions in professional societies like the Institute of Mathematics and its Applications, directed the Bath Taps into Science festival and been part of the Vorderman Committee, which produced a report in 2011 about recommendations for mathematics education.

# In conversation with Vernon Morris

Meet Vernon Morris; a chemist, a mathematician and an active contributor to making everyone aware of the race gap in academia and industry.

Given the successes of his academic career, it is surprising to hear that Vernon Morris “never planned to go to college. A lot of folks where I was growing up, they didn’t really go to college. They went into the air force or they tried to find a job.” He was good at boxing when he was at high school and thus was given two options: either join the air force (“because they had a good boxing programme”) or become a professional boxer right away.

Vernon working on his project; Image reproduced with his permission

But fate intervened, and Vernon started at college in Atlanta. “I left for college, but I didn’t know what I wanted to major in.” He was on his way to his part-time job when, cutting through the Department of Chemistry, he bumped into a professor who was so intrigued by him that he offered him a scholarship. “But there was a catch. You have to major in chemistry and you have to major in maths, because you can’t do chemistry without maths. I accepted his offer.” This professor was Henry McBay, a man who is responsible for more African-American PhD students (over 50) than any other single person. It doesn’t come as a surprise, then, that Vernon considers him as a role model: “Henry McBay got me on the right path”.

# In conversation with Talitha Washington

Talitha Washington is a professor of mathematics at Howard University who is passionate about improving ethnic minority access to STEM subjects in the USA. Talitha, whose name comes from the Biblical verse “Talitha cumi”, literally meaning “little girl, get up!”, introduces herself as an activist, a mathematician, and a professor.

## Talitha, the activist

Talitha Washington’s work on Elbert Frank Cox, the first black person in the world to earn a PhD in mathematics, has been shared on radio and television stations, as well as in the Notices of the American Mathematical Society. They both grew up in Evansville, Indiana and both went on to teach at Howard University. Image reproduced with her permission.

The lack of diversity in sciences and mathematics is a sensitive topic, and how different generations interact with racism has drastically changed over the past few decades. “Typically, older generations, like our parents, used to say you should ‘act like a duck and shake off the water’, meaning if you encounter racially charged situations you just grit your teeth and persevere through it: you try not to let it affect you.” Talitha says that for people of her generation this was also the norm, even though it did not seem fair. However, for the younger generations, the situation is a little different. They have grown up with a black president in the United States and the promise that if you work hard you will be rewarded, independent of the colour of your skin. So if they “encounter racially charged situations they may or may not know what to do, or how to handle it. Instead they will say, ‘this is not for me — I am going somewhere else where I am already accepted, because this is not how it should be’. And we don’t want to lose the younger generations in STEM because of that.”

# In conversation with Jonathan Farley

Jonathan Farley is a mathematician from New York who completed his bachelor’s degree at Harvard and graduated with a DPhil from Oxford in 1995, after winning Oxford University’s highest awards for mathematics graduate students, the senior mathematical prize and Johnson university prize. His research interests include lattice theory, the theory of ordered sets and discrete mathematics. Whilst this may sound quite pure, there have also been some interesting applications. For example, Jonathan published a paper in 2003 called ‘Breaking Al Qaeda Cells: A Mathematical Analysis of Counterterrorism Operations’ analysing when a terrorist network becomes disrupted and dysfunctional using order theory. This attracted some media and military attention, including the Ministry of National Security in Jamaica implementing some of Jonathan’s ideas in smuggling networks.

## Lattice theory

When Jonathan was in high school, his class completed a questionnaire which would tell them their ideal vocation and his result was a mathematician/statistician. “That was the first time I really thought of becoming a mathematician, and since my parents are both professors, I only ever thought of becoming a mathematics professor”. Jonathan’s mother is Jamaican and has a PhD in American history, his father is from Guyana and has a PhD in economics which he completed at the LSE.

Simple example: lattice of subsets of {x, y, z}, ordered by “is subset of”. Wikimedia Commons user KSmrq, CC BY-SA 3.0

Jonathan’s passion for lattice theory started during his undergraduate degree where his advisor was Garrett Birkhoff – who was one of the leading figures in 20th century lattice theory. “I had a lot of interesting conversations with him. I wish now that I had known more math then, to more fully appreciate those conversations.” Although Jonathan admits lattice theory is a bit of a dying field, he recently visited someone in New York City who has used lattice theory in cancer research. “A lot of mathematicians will say, ‘Oh, this work can be applied to x or y’, and if you go to the people in those fields, they don’t know anything about it. However, this does seem to be a real application; they’re working with people who are actual medical doctors”.

## Black mathematicians

There is a large drop in the number of black students continuing to study mathematics after high school, and Jonathan believes this is due to them not knowing any mathematicians or not being aware that it is a possible career. “In America, you do have many middle class African-Americans, but you also have a lot of ones who are poor, so they’re going to do whatever is most lucrative and becoming a mathematics professor or a mathematician probably is not what they’re thinking about.” Despite Jonathan not knowing many black mathematicians himself at the time, he never felt isolated due to his knowledge of antiquity and his parents coming from a community of scholars. “I didn’t need to see it directly, or work directly with black mathematicians. Although when I was in Oxford, I did try to do my part with the Oxford Access Scheme, the purpose of which was to bring non-traditional students to Oxford, or at least expose them to the university, so they would consider applying.” Jonathan believes it is particularly important for schools to highlight scientists from other parts of the world and the long history of mathematicians working in Africa, because they certainly do exist!

At the very top level, Jonathan hasn’t yet seen any black mathematicians as great as David H Blackwell and J Ernest Wilkins Jr (who completed their PhDs in the 1940s), however he is optimistic and thinks the time will come. In terms of academia, the number of black mathematicians does seem to be increasing. For more information on this, Scott Williams runs the website ‘Mathematicians of the African diaspora”.

Image: Jonathan Farley, by permission

Jonathan has seen first-hand the extent of racist attitudes to black mathematicians in the USA, having once been detained by police at MIT for ‘looking like a bank robber’ and being forced to move and resign his job at Vanderbilt University because of death threats and other threats by supporters of the Ku Klux Klan. He shared several of his experiences, and those of other black mathematicians, in an essay here.

# In conversation with Tanniemola Liverpool

Tanniemola Liverpool is a professor of theoretical physics in the School of Mathematics at the University of Bristol. As one of the few black mathematics professors in the UK, and as somebody who helped set up the first access scheme to focus specifically on ethnic minorities, his is an authoritative voice on diversity in academia. We spoke with him in September about his experiences, both as a student and as a professor, and about what he thinks are the most important factors in creating a more representative mathematical community.

# In conversation with Cédric Villani

Early on a February morning, we’re standing outside one of the many trendy cafes in Fitzrovia. Down the street we spot a man striding our way, wearing a full suit, a hat, a giant spider brooch and hastily tying a cravat. It could only be superstar mathematician Cédric Villani.

Cédric is passing through London on his way back from the US, but this is no holiday. In his two days here, he is attending a scientific conference, giving a public lecture, and taking part in a political meeting. His packed schedule leaves the increasingly-busy Fields medallist just enough time to join us for breakfast.

## Fields medal

One afternoon in early 2010, Cédric was in his office at the Henri Poincaré Institute in Paris, getting ready to pose for publicity photographs. The photographer, from a popular science magazine, was setting up his tripod when the office phone rang. Cedric leant over and picked it up. It was Lázló Lovász, president of the International Mathematical Union.

Fields medal ceremonies are held every four years, and six months before each ceremony, the winners are alerted by telephone about their success. During these six months, they are sworn to secrecy, but with the photographer in the room, Cédric suddenly realised that he might be in possession of the shortest-kept secret ever. By some miracle, the tripod had proved sufficiently interesting for the photographer, or perhaps he didn’t follow the English conversation, and the secret remained safe.

If you try too hard to win a Fields medal, you will fail.

Cédric had first realised that winning the Fields medal was a possibility at some point in 2004, when he was 31. Fields medals are only awarded to mathematicians under the age of 40, and until the phone call arrived, Cédric only placed his chances of winning at around 40%. “The prospect of winning the medal does put some pressure on you during your 30s. But everybody knows—it’s part of the common mythology—that if you try too hard to win it, you will fail.”

In August 2010, Cédric was officially awarded the medal at the International Congress of Mathematicians in front of 4000 mathematicians and journalists. Finally, he was allowed to celebrate: he did so by taking a dozen colleagues to a fancy restaurant in Germany, thereby relieving himself of half the CAN\$15,000 prize money.

## The Boltzmann equation and Landau damping

The Boltzmann equation can be applied up where the air is clear less dense. Image: public domain

While enjoying a hearty breakfast, Cédric explains his research to us. “In this room, we are surrounded by air. You can use the Navier–Stokes equations to describe this air. But at higher altitutes, where the atmosphere is more dilute, these equations do not work so well. Here, it is better to use the Boltzmann equation.” The Boltzmann equation describes the statistical behaviour of a gas, and Cédric has worked on two areas related to this equation: the influence of grazing collisions, where two particles pass very close to each other; and on the increase in entropy as time passes.

Cédric’s other work, completed with Clément Mouhot, looked at the mechanics of plasmas: high-energy soups of electrons and positively-charged ions which are formed by superheating gases. Roughly speaking, if a plasma is exposed to a brief electric field, then the electric field will become very small as time goes by. This decay effect is called Landau damping. In the 1940s, Lev Landau proved that this damping occurs for a linearised approximation of a plasma. Cédric and Clément proved this result for the full non-linear system of equations.

It was the work in these two areas that led to Cédric being awarded the Fields medal, although he has worked in other areas as well. Imagine you have a large pile of sand and a hole to fill (with the same volume as the sand). How should you go about moving the sand to fill the hole, while minimising the total work you have to do? This is an example of an optimal transport problem.

He used the ideas of entropy from his study of the Boltzmann equation and applied them to this problem, and used this to establish a link between the non-Euclidean curvature of a manifold and properties of the entropy. This led to a “whole bunch of research related to non-Euclidean geometry”.

## Career choices

Academia is where my heart belongs.

If the young Cédric had had his way, his research life would be very different. “When I was a kid, I wanted to go into palaeontology. I recently had a great discussion with Jack Horner, the world’s most famous expert on the subject—‘Mr Dinosaur’, and it was like reconnecting with my youth.”

So is he happy in mathematics academia? “Academia is where my heart belongs. I like industry, and I sit on the advisory boards of several companies, but I’m an academic guy. My research has not had an application so far that I am aware of. But, with applications, when they come it will be much later.”

Traces of Cédric’s early passion can still be spotted though. He owns a cuddly toy dinosaur called Philibert, and leaves maths books open to keep him entertained. Years later, he found that Alan Turing, one of his greatest heroes, used to do the same with his teddy bear at university.

Grumpy Gauss, oil on canvas. Christian Albrecht Jensen (1840)

In fact, Turing is the hero in his recently-penned graphic novel,  Les Rêveurs Lunaires. Excited readers will be disappointed, however, as “even though England is everywhere in the book, English publishers have not yet been interested in making an translation.” This is a double-shame, as you will remember from Chalkdust issue 04 that comic books about maths are hot’.

He is, however, less sure whether he would like to travel back in time to work with Turing or other mathematicians. “People like Gauss—so fascinating, so superhuman. But he was known for being rather grumpy; maybe it would not be so pleasant! Then take Riemann—a genius! But a bit depressive; maybe he was not so fun to work with. I’m not sure if he would want to see me.”

## A day in the life of a Fields medallist

Life is rarely routine for Cédric. In a usual year he travels to 20–25 countries, and has roughly 30 different appointments each week. When he can, he enjoys a quiet family breakfast at home. The contents of this breakfast have not changed since he was a child, and include bread, jam and hot unpasteurised milk. For today, however, he makes do with a full English with scrambled eggs.

I never give fashion advice. I always tell people: “find your own way”, as I did find my own way.

Dairy products seem to feature heavily in Cédric’s day-to-day life. Impressively, he is able to visualise every shelf in his favourite cheese shop and name, in turn, every item on sale. This is very important to him, as otherwise he could return home from grocery shopping to find himself without one of his many favourite cheeses.

He is in London to give a lecture to the public, something that he spends a large amount of time doing these days, “much more so than to mathematicians. But both are good: different feelings, different preparations.” Overall, since winning the Fields medal and gaining fame, Cédric claims that his time for research has been “divided by hundreds”.

Indeed, the public lecture is not his only commitment in London. He is currently attending a meeting at the Royal Society about the numerical abilities of animals. This meeting included great revelations about the mathematical abilities of frogs—evidenced through their calls involving sounds of varying number and length—as well as fish, bees and chimpanzees. “One of the crazy things that emerged from this conference is that the tendency to put small numbers on the left and large numbers on the right is not merely a side effect of how we write numbers. You can also find this—in some sense—in newborn chicks and fish.”

When in France, Cédric is recognised everywhere he goes, and is (still) posing for photographs. He is regularly featured on the covers of science magazines, and is often confronted by giant billboards of his face. If you are planning on winning a Fields medal, do not panic: he assures us that you will quickly get used to this.

## Politics

Cédric enjoying a popular maths magazine. Image: Chalkdust

When we meet Cédric, the French election is in full flow. As part of his stay in London, he is attending a meeting for the candidate he describes as the “young, centrist guy”. He is one of seven scientists on a board that provides scientific policy advice to the European Commission. However, he doesn’t recommend becoming too involved in politics, as he thinks there is no way to find time to pursue both a serious research career and a serious political career.

“The current political climate is far from science in general. Science, as a field, is much more respected by society than politics. So there is reputation to be lost by going into politics. But the most popular politician in French history is Napoleon, and he was keen on mathematics, and a big protector of mathematicians and scientists. He was elected to the academy of sciences, attending when he could, and enjoyed discussions with many of the best mathematicians of his time. But he was always late…”

Keen not to be late himself, Cédric finishes his eggs and heads off to his next commitment. It would seem, however, that Cédric does not always listen to his own advice: in June he became an elected member of the French parliament, as a member of the young, centrist guy’s party.

TD, Scroggs and Yiannis The Undergrad enjoy Cédric’s company. Image: Chalkdust

# In conversation with Olubunmi Abidemi Fadipe-Joseph

Olubunmi is a Nigerian mathematician who gained her BSc Mathematics (first class honours) in 1995 and MSc in mathematics in 1999 from the University of Ibadan (the first university in Nigeria). She gained her PhD from the University of Ilorin, Nigeria in 2005, where she is currently a lecturer in the Department of Mathematics. She decided to study maths because “I loved doing calculations and everything related to mathematics right from my primary school. I always wanted to be a teacher, but then I discovered that as a lecturer I could do some research and so I carried on with my academic career. My father, a teacher, was my role model”. Continue reading

# In conversation with Nazar Miheisi

Dr Nazar Miheisi is a teaching fellow at King’s College in the Mathematics Department, currently doing research in the field of Analysis (specifically, Operator theory and Complex function theory). Naz, as he likes to be called, is a black researcher in an environment where most of his colleagues and peers are rarely from any ethnic minorities. Naz, who has several academic publications and completed his PhD thesis on convolution operators and function algebras, shared his experiences with us;  from the time he was just a kid in a state school in Wembley, to his Engineering degree at King’s College and his academic career. Continue reading