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NPR

The Salt

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Mar 14, 2015

by:

L. Carol Ritchie

We bring you this story in case you want to get baking.

That's because Saturday is Pi Day — but it's not just any pi day.

It's March 14***** of the year '15, or 3-14-15 — the first five digits of the number pi. It's a confluence that won't happen again for a hundred years. Math geeks are excited.

"Pi has certain fascination, due to the fact that its digits appear to be unpredictable," says Po-Shen Loh, a math professor at Carnegie Melon University and U.S. coach for the International Mathematical Olympiad. "It's usually the first irrational number that students encounter."

Pi is not just irrational — meaning it can't be written as a simple fraction. It's transcendental. In math, transcendental means it's properties are not algebraic, but the adjective is just as true in the non-math meaning. Pi is transcendent, fantastic and otherworldly. It's the circumference of a circle — a shape of infinite perfection — divided by its diameter, and it's true no matter what size the circle is.

"It's magical," says Loh, getting a little carried away. "No, no. It's not magical. It's mathematics. ... It's beautiful that you have a transcendental number that's also extremely useful."

To get excited about math this week, students around the country have been reciting pi, eating pie, throwing pies, enjoying pi played on the piano and listening to pi rap by artist Pi Diddy.

At the San Francisco Exploratorium, where Pi Day originated in 1988, visitors will be admitted free for a pizza-pi-dough-tossing contest, a pi parade and special pie serving on Saturday.

Enthusiasts will also mark pi down to the second on Saturday. At 9:26 and 53 seconds, both a.m. and p.m., pi will be represented to 10 digits: 3.141592653.

Purists will argue that pi second comes at 9:26.54 — the next digit in the line is 5, and they will say we should round up.

That argument will likely never be resolved — kind of like pi itself. The ancient civilizations of Egypt and Babylonia knew about it — some say they used it in building the Great Pyramid at Giza — although they only came close to exactly pi. In 2013, mathematicians calculated the number to a mind-boggling 12.1 trillion digits.

And they could keep going. Forever.

Loh, who feels no need to memorize those digits, will spend Pi Day at a math conference. He is developing an interactive Wikipedia of math to help students of all levels. He's so devoted to getting people excited about math that even his phone number is a version of pi.

******By complete coincidence and to the delight of physicists, March 14 is also Albert Einstein's 136th birthday. The town of Princeton, N.J., where Einstein lived for 20 years, will hold its annual Einstein lookalike and pie eating contests.*

Copyright 2015 NPR. To see more, visit http://www.npr.org/.

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