University of Rochester

Academic Minute: Pi Day

March 14, 2011

Essay by C. Douglas Haessig
Assistant Professor of Mathematics

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In many academic circles, today's date is cause for celebration. Yes, March 14th is Pi day, named after the mathematical constant Pi, and defined as the ratio of a circle's circumference to its diameter. 3.14159 and so on, the digits continue on forever with no known pattern.

So why is pi, among all the mathematical constants, important enough to be celebrated? Gastronomically speaking, we all know what dessert to bring to the party. Mathematically speaking, it has to do with geometry. Geometry has two fundamental shapes, lines and circles. This ubiquity places pi in many equations which describe reality. In physics for instance, pi appears in the equations used to describe a static universe. In geology, pi appears in the evolution of meandering rivers, an observation first pointed out by Albert Einstein, whose birthday happens to be today.

Pi is like a Hollywood star, appearing in numerous movies and admired by many. And like stars, pi has its critics and groupies. Bob Palais, a mathematician at the University of Utah, wrote an article titled "Pi is Wrong!". Its thesis focuses on a particular pi groupie, the number two. See, if you look at many of the equations where pi appears you'll see the number two sitting next to it. This frequency suggests defining pi as the circumference divided by the radius, a number equaling two times pi. Of course, this would mean celebrating Pi Day instead on June 28th, with probably twice as many desserts. Not a bad deal.




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