03/12/2015 11:14 am ET Updated Dec 06, 2017

Why You Need to Eat Pie This Saturday

Give me 3.14 minutes to explain.

This Saturday is March 14, 2015. Every March 14 the entire world comes together to celebrate Pi Day. (Yeah, right, we're lucky to get, like, five people.) The "pi" referenced here is that magic number that you may remember from math class. This picture should jog your memory:


OK, OK, ignore that tasty pie on the left and focus instead on the pi on the right -- the ratio of a circle's circumference (distance all the way around) to its diameter (width of the circle).

A reasonable approximation of pi is 3.14. But don't take my word for it; find any circular object and measure C and d and you'll get your own approximation of pi. But that's not the only way. Since about 2,000 B.C. all sorts of people -- not just mathematicians -- have found other ways to approximate pi.

Part of the allure is that pi is irrational. According to Merriam-Webster, that means pi is "not thinking clearly; not able to use reason or good judgment." No wonder we can't have just one slice of pie!

But to us mathematicians, "irrational" means not rational, meaning the number can't be expressed as the ratio of two "whole" numbers. For example, 0.1111... is rational; it's equal to 1/9. But not so for pi; it can never be written as p/q for any combination of whole numbers p and q.

Actually, it gets even worse. Unlike 0.1111..., which has a repeating pattern, the decimal expansion for pi, 3.14159265358..., doesn't contain any patterns. The numbers just keep jumpin' around senselessly. (Maybe pi is irrational in the dictionary sense of the word!)

But we humans are pattern seekers. So here's how this all comes back to this Saturday:


Yup, 3/14/15 at 9:26:53 a.m. is "pi time." (Actually, it's the start of "pi time," since the next two digits are 59.) So get those pies ready, because on Saturday morning you'll have a once-in-a-lifetime chance to live through pi.

Oscar Fernandez is an assistant professor of mathematics at Wellesley College. He is the author of Everyday Calculus: Discovering the Hidden Math All Around Us, and also writes about mathematics on his website You can follow him on Twitter @EverydayCalc.