Tomorrow, March 14 (3/14) is Pi Day. I blog about Pi Day every year because I like Pi Day. I know a lot of people use it as an excuse to eat pie and lately I notice most of the Pizza places run Pi Day specials on their “pies.” But of course everyone knows by now that Pi Day isn’t about pies.
Like all days that repeat every year, I’ll probably repeat some details about Pi again this year, but hopefully I’ll touch on some new stuff. There wasn’t always a Pi Day. In 1988, physicist Larry Shaw launched the pi-partying day at the Exploration Science Museum in San Francisco. Every year, on March 14 (2/14) staff and visitors walk a circular parade (the diameter of the circle is like Pi times its circumference) each holding one of the infinite numbers of Pi. It didn’t become a national event until 2009, when the House of Representatives passed Resolution 224 with the goal being to increase interest in math and science.
The ancient Babylonians knew of pi’s existence nearly 4,000 years ago. A Babylonian tablet from between 1900 B.C and 1680 B.C calculates pi as 3.125, and the Rhind Mathematical Papyrus of 1650 B.C, a famous Egyptian mathematical document, lists a value of 3.1605. The King James Bible (I Kings 7:23) gives an approximation of pi in cubits — a unit of length, corresponding to the length of the forearm from the elbow to the middle finger tip (estimated at about 18 inches or 46 centimeters.)
The Greek mathematician Archimedes (287-212 B.C.) approximated pi using the Pythagorean theorem — a geometric relationship between the length of a triangle’s sides and the area of the polygons inside and outside circles.
To back up a bit, Pi (π) is the ratio of a circle’s circumference to its diameter. Because it is irrational, it can’t be written as a fraction — it is an infinitely long, non repeating number. The record for the most digits of pi memorized belongs to Rajveer Meena of India, who recited 70,000 decimal places in 2015.
Because pi is an infinite number, humans will, by definition, never determine every single digit of pi. However, the number of decimal places calculated has grown exponentially since pi’s first use. The Babylonians thought the fraction 3 ⅛ was good enough in 2000 B.C., the ancient Chinese and the writers of the Old Testament seemed perfectly happy to use the integer 3. By 1665, Sir Issac Newton had calculated pi to 16 decimal places. The advent of computers radically improved humans’ knowledge of pi. Between 1949 and 1967, the number of known decimal places of pi skyrocketed from 2,037 on the ENiAC computer to 500,000 on the CDC 6600 computer in Paris. Late last year, a Swiss company used a multithreaded computer program to calculate 22,459,157,718,361 digits of pi over the course of 105 days.
I mentioned last year that there is a resistance movement growing…. some argue that pi is a derived quantity, and that the value tau (equal to twice pi) is a more intuitive irrational number. Tau directly relates the circumference to the radius, which is a more mathematically consequential value. Tau also works better in trigonometric calculations — tau/4 radians corresponds to an angle that sweeps a quarter of a circle, for instance.
So if you’re interested in joining the resistance movement, or you’re just looking for another day to celebrate, meet me back here on Tau day — June 28.
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