Math Enthusiasts Find Pi Pops Up In The Most Unexpected Places

RENEE MONTAGNE, HOST:

Today is 3/14, also known as Pi Day. NPR's Eyder Peralta reports on why pi still matters. EYDER PERALTA, BYLINE: Here's how mathematician Carlos Castillo-Chavez describes pi. CARLOS CASTILLO-CHAVEZ: It brings you into the world of mathematics, which is magic, mysterious and exciting.

PERALTA: Pi represents the ratio of a circle's circumference to its diameter. But Castillo-Chavez, who studies epidemics at Arizona State University, says pi is used to study everything that cycles. In his own work, he uses pi to try to understand why certain strains of influenza seem to reappear every 20 years. In math, he says, pi pops up in the most unexpected places.

CASTILLO-CHAVEZ: Pi, with its infinite number of digits, is an introduction to the kinds of mathematics that we do, which often involve a study of infinite processes.

VI HART: Pi is not special. Yeah, pi can be fun, and I'd never deny you your desserts. PERALTA: Math geek and YouTube star Vi Hart - Hart, a recreational mathematician, has made a habit of posting anti-pi videos. Her beef? There are plenty of other mathematical constants that are just as infinite. And pi doesn't make sense, she says. The circumference of a circle is 2-pi-R. Wouldn't it be simpler, she says, if we created a new constant that makes equations easier? But I remind Vi that her name rhymes with pi, and maybe she's really a fan. HART: Some people might think there's a conspiracy there that all along I've only been pretending to hate pi, but really I'm just trying to rally people behind the cause of pi through manufactured outrage. PERALTA: That's just a theory, she says. But she also did collaborate with math artist John Sims on what they call the, "Pi Day Anthem." (SOUNDBITE OF SONG, "PI DAY ANTHEM") JOHN SIMS: (Singing) 3.1415...

PERALTA: Eyder Peralta, NPR News.