Opinion – Marcelo Viana: Who cares about the math of card tricks?

Stanford University researcher Persi Diaconis interrupted his presentation at the event commemorating the 70th anniversary of Impa (Institute of Pure and Applied Mathematics) last week with a question rarely heard at a research conference: “Who do you care about this?”

Diaconis is a unique character in the world of mathematics, with an unusual personal and professional trajectory. I first met him in 1998, when we both gave plenary lectures at the International Congress of Mathematicians in Berlin.

We met again in person 15 years later, when he gave a popularization lecture on the mathematics of coincidences at the 1st Congress of Mathematics of the Americas, which I helped organize in the Mexican city of Guanajuato.

Born in 1945, at the age of 14 Diaconis left home to travel with the magician and conjuror Dai Vernon, alongside whom he performed in circus shows. At the time, he dropped out of school, of course. But he returned ten years later, determined to learn the math behind the card tricks he’d discovered in his wanderings.

He graduated from the City University of New York in 1971 and received a PhD in mathematical statistics from Harvard University three years later. They say that during this period he supported himself and paid for his studies by playing poker on the ships that connected New York to the south of the United States.

Today he is an almost legendary leader in the world of statistical research, in addition to continuing to be an expert juggler.

In some of his most famous works, published in the 1990s, Diaconis proved several rigorous mathematical rules about shuffling, and what it takes to make the order of the cards genuinely random.

“I’m sure the rule that you only need to shuffle seven times will be written on my grave!” he commented jokingly in conversation. That was precisely the topic of his lecture at Impa, by the way. And he even answered his own question about who cares about it.

“Well, a lot of people play cards, and people who shuffle the deck care how many times they shuffle the cards. Basically, they changed the rules in Vegas because of a theorem we proved!” This story deserves to be told, but it will have to wait for next week.