IT'S PI DAY!!!

Pi is the famously irrational number that represents the ratio between a circle's circumference to its diameter. Fractionally it is 22/7, but it's far more commonly represented as the string of literally endless digits: 3.14159.... Today, Pi has been calculated out to 31.4 trillion digits. The digits are countably infinite, meaning they go on forever in no repeatable pattern, but we can calculate them. Frankly I'm glad computers can do that for us.

Pi as a concept is ancient, though its value has varied over time. Ancient Babylonians approximated the value as 3, and there is one tablet that puts it at 3.125. Ancient Egypt had a slightly different value for pi at 3.16 (more precisely as 256/81). This value comes from an ancient papyrus scroll called the Rhind Mathematical Papyrus (1650 BCE).

The Egyptian Rhind Mathematical Papyrus.
Photo credit: The BBC

The famous Greek mathematician Archimedes of Syracuse (287–212 BCE) even tried his hand at calculating pi, but was only able to place limits on its values and did not calculate an exact number. He bounded it between 3 1/7 and 3 10/71, or between 3.140845... and 3.142857.... He wasn't wrong, but he wasn't as precise as later mathematicians were. 700 years later, Chinese astronomer and mathematician Zu Chongzhi calculated the ratio between circumference and diameter to be 355/113, or 3.1415929.... The details of his work are unknown because his book has been lost to time, but historians believe it was computationally complex, "involving hundreds of square roots carried out to 9 decimal places."

It wasn't until 1706 that the Greek letter "pi" was used to represent this intractable but necessary number. While initially introduced by William Jones, mathematician, Fellow of the Royal Society, and friend of Sir Isaac Newton, it was Swiss mathematician Leonhard Euler who popularized it in 1737.

Leonhard Euler, painted by Jakob Emanuel
Handmann, 1753.

In honor of the 3.14 basic number, on the fourteenth day of every March (3/14 in the MM/DD format), we celebrate PI DAY. It is by far the most glorious of all March holidays (in the opinion of this author, at least). I'm far from the only one who thinks this though! In true mathematical style, MIT releases the decisions of its undergraduate freshman class on this date every year, and the emails are sent out at precisely 1:59 PM eastern time. In 2009, a non-binding resolution in the House of Representatives declared March 14, 2009 as National Pi Day in an effort to engage students in mathematics. Also, it's an excuse to bring pie into work and share it with your coworkers. What could be more fun?

Honestly, the answer to that question could be having participated in the very first Pi Day celebrations. Pi Day as a fun holiday isn't an old idea; the first known, large-scale celebration of the arithmetical anomaly was in 1988 at the Exploratorium in San Francisco. Dr. Larry Shaw was a physicist who worked there, and it seems like he used the day as an excuse to get the staff and public together in the building to eat cake. After walking around one of its circular spaces, everyone stopped and began to devour the many fruit pies around the room. The Exploratorium still holds Pi Day celebrations to this day, though they are more extensive and engaging now, with games, talks, activities, and even a band! Fortunately, pie eating is still involved.

Pi actually has a rival for best circular approximation number. Tau is a ratio that relates a circle's circumference to its radius rather than its diameter. Effectively, Tau is just 2*Pi, or 6.283185.... Tau also has a holiday celebrated on June 28th (6/28), but it is less well-known, probably because it doesn't have delicious baked goods associated with it. Supporters of Tau argue that it removes confusion when switching from radians to degrees when describing angles, and that trigonometric functions would have a period of Tau instead of 2 Pi, which is easier to understand conceptually. Pi is winning the popularity contests now, but that could change in the future.

Regardless, Pi Day is a fun time to celebrate the math in your life and learn about the history of the number we all know by name.

I brought an apple pie into work today to celebrate
Pi Day. It was delicious!