SCIENCEThe Irrational Number That Somehow Became the World’s Most Beloved Holiday4 min read

The Number That Never Stops

Pi has been messing with human minds for roughly 4,000 years. The ancient Babylonians were fussing over it. Egyptian mathematicians were wrestling with it. And here we are, still at it — no closer to the end.

What makes pi so captivating isn’t what it is. It’s what it refuses to do. As the ratio of any circle’s circumference to its diameter, pi begins at 3.14159 and keeps going. Forever. No repeating pattern. No tidy endpoint. It’s an irrational number in every sense of the word, and it shows up everywhere — from the orbits of planets to the equations behind MRI machines.

One Physicist and Some Fruit Pies

The official Pi Day origin story starts at San Francisco’s Exploratorium in 1988. Physicist and museum curator Larry Shaw — known to colleagues as the Prince of Pi — pitched the concept at a staff retreat. The first celebration was charmingly low-key: fruit pies and tea, served at exactly 1:59 p.m., those three digits being what follows 3.14 in the sequence.

What grew from that afternoon was something nobody planned. Shaw started staging “pi-rades” — staff and visitors marching around the museum building, each person representing a successive digit of pi, Shaw out front leading the procession. He kept the tradition going until his death in 2017. The Exploratorium still holds Pi Day events every year: lectures, concerts, pi processions, and dessert.