Happy Pi Day!

Pi Day is one of my favorite unofficial holidays! (May the 4th is a really close second)

March 14. Or 3/14 as we commonly write it in the US is the shorthand for the number pi. Pi is the ratio of a circle’s radius to its circumference. For those of you who haven’t taken or thought about geometry in a long time the formula for the Circumference of a circle is

C = 2πr

I know that since you learned this in 7th grade you assume it’s unremarkable. But π really IS remarkable. For every circle – from the iris of your eye, the wheel of your tire, to the moon – you can calculate the distance around it if you know the distance from the center to the edge. And it’s always multiplied by 2π. This is very handy if you’re trying to make four wheels that are the same size. But, there’s a catch π isn’t a number or a quantity that exists. It just goes on and on. We can approximate it, but we can’t really know where it ends.

Isn’t that mysterious? Obviously, the distance around a circle is finite. But that little number π, which can be approximated as 3.14 just goes on and on and on (for more than 22 trillion known digits. Thanks Emma Haruka and Google.)

If you know a little bit of number theory, you’ll know that there are a few (actually there’s an infinite number of them, but most of them don’t come up in our daily life regularly and none of them as often as π) of these “irrational numbers” which is to say numbers that goes on to an infinite number of digits and on and can’t be approximated by a fraction. It’s just this ratio that appears (frequently) in nature.

For people who love math, π is a mystery (kind of like Stone Henge). The ratio puzzled the ancient Babylonians, Egyptians, Archimedes, it’s even mentioned in the Hebrew bible a couple of times. People have tried to approximate it, to rationalize it, to formalize it, and know it with certainty – only to find with certainty that it just goes on and on irrationally (which was proven by Mathematician John Hambert in the 1760s). It’s used in our modern world to encrypt our communications and internet transactions and to build our buildings. It’s everywhere!

What I love about π (and math) is that it gives you this glimpse of the infinite in our finite world hidden in plain site every time you eat off a plate, open a jar of play dough, or drive a car.

If you’d like to learn more about π here are some recommendations I have. Also, I hope you enjoy a piece of pie in celebration of this crazy number!

Here’s Looking at Euclid by Alex Bellos (I love Alex Bellos’s writing about math. It’s very accessible whether you’re into calculations or not, the story of numbers is fascinating!)

The History of Pi by David Wilson


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