6 JANUARY 2007, Page 4

DIARY

MARCUS DU SAUTOY Iwas ready for the depression but it still doesn't stop it hitting. Doing the Royal Institution Christmas Lectures was such an exhilarating, exhausting six-month roller-coaster ride. The climax was a two-week adrenaline-charged loop-the-loop staging what felt like five wild maths pantos. Then the last lecture is given, filmed and delivered and bang, the ride comes to an end and I'm spat out the other side on my own again. The camaraderie of staging a show is a very temporary thing. I remember as a student the feeling of isolation after the last night of putting on a play. You promise to see each other soon. Take phone numbers. Swear to have them round for dinner. But then everyone goes their different ways. For me the contrast is probably starker than for the rest of crew. Doing maths is by its very nature a lonely pursuit. You have to hide away, trying to achieve that level of Buddhist meditation that lets you escape into the mathematical world. Many mathematicians hanker after that escapism, but the isolation can be hard. My fantasy when the mathematical going gets tough has always been to chuck it all in and join the Lecoq Mime Theatre in Paris. The Christmas Lectures were a way of fulfilling both my fantasies: doing maths and theatre.

what is it about mathematics that brings out the nutters? The first emails I get after the broadcast of the lectures are filled with mad theories about cabbalistic primes or how the Koran already holds the answer to the mathematical shape of the universe. I even have a crazy person on the phone harassing me with some new logic called Je Suis which he thinks will help my research. 'If you take the "I" out of this logic you'll see the message the universe is trying to communicate to us.' New Year's resolution: must go ex-directory. Ever since I started interacting with the media, I've been inundated with crazy theories. My first ever article for the Times prompted an abusive letter from a Miss Quick in Croydon attacking the arrogance and ignorance of academics like me sitting in their ivory towers. I was so taken aback by the abuse I decided never again to raise my head above the parapet. At lunch in All Souls that day I bumped into one of the history fellows who also wrote regularly for the Times: 'Nice article yesterday. Got a letter from Miss Quick yet?' My skin thickened a little bit that day.

whenever I get the fixture list in August for Arsenal, the first question is: are we home or away on Boxing Day? Alas, this year we were away at Watford. So post-Christmas football was replaced by a trip to the dogs at Walthamstow. My tenyear-old son, having attended my Christmas Lecture on the maths of betting, was, I think, expecting me to have some winning strategy for raking in the cash. I explained that with 12 races and six dogs in each race, if we randomly chose dogs we should get two wins. Tomer was not impressed. He was all for choosing dogs based on form and spent the afternoon engrossed in the Racing Post. My three-year-old girls were more interested in choosing dogs based on the colours they were racing in. Thanks to Not So Jolly coming in at 6:1 in a nice shade of orange, we left the track only £2 down.

I'm a big fan of Channel 4's Faking It. I've always had this idea of taking one of the bookies standing on their boxes at Walthamstow and seeing if in four weeks I could train them to give a convincing maths seminar at a conference. My wife has heard my spiel on my research so many times that she can do quite an uncanny impression of a mathematician: 'Well, the p-adic representation of the Lie algebra whose zeta function encodes an elliptic curve. . . . 'But I think it's the questions that would rumble the faker. Although I do love that story of Einstein's driver, who said that he had heard Einstein's talk so many times that he thought he could give it. So that evening Einstein agreed to let his driver give the talk. At the end of the presentation a rather penetrating question was fired at the speaker. He coolly replied, 'That's so straightforward even my driver could answer that one.'

Result. The man at the till next to me in Sainsbury's did a double take, clearly making a desperate attempt to recall where he knew me from, then blurted out, 'You're on the telly.' I hugged him in my moment of excitement, then had to explain that mathematicians don't get out much. Shame I don't get the same recognition for the hard slog I've put in proving theorems over the years: 'Hey, aren't you the guy who proved the rationality of zeta functions of p-adic analytic groups?' Dream on.

Acouple of Spectator readers have pointed out with varying degrees of civility that I can't add up. The Travelling Salesman Problem that I set in my puzzles for Christmas has a shorter route (234m) round the penguins than the one I drew in my answers (238m). It only goes to confirm the point of the puzzle, that mathematicians don't have a clever way to find the shortest path. Anyway, well done to all those who spotted the shorter path.