Why should we care about pi? The number 3.14… may be irrational, but it can be found all over the natural world. It appears everywhere there's a circle, such as the disk of the sun, planets, and even the earth. Pi is in the physics that describes waves, such as light and sound. Pi even appears in the spiral of the DNA double helix!

On Pi Day you’ll see a lot about pie-eating contests, and hear about competitions over who can memorize and recite pi to the furthest digit (the mathematician’s equivalent of a spelling bee), but taking a day to honor this number is about much more than this. Perhaps the most poetic description of why we celebrate pi comes from Steven Strogatz in The New Yorker:

“The beauty of pi, in part, is that it puts infinity within reach. Even young children get this. The digits of pi never end and never show a pattern. They go on forever, seemingly at random—except that they can’t possibly be random, because they embody the order inherent in a perfect circle. This tension between order and randomness is one of the most tantalizing aspects of pi.”

The truth is that pi appears where you would least expect it. For example, who would have guessed that pi plays a part in the meandering shapes of rivers? Check out what Natalie Wolchover of LiveScience has to say about it:

“A river's windiness is determined by its "meandering ratio," or the ratio of the river's actual length to the distance from its source to its mouth as the crow flies. Rivers that flow straight from source to mouth have small meandering ratios, while ones that lollygag along the way have high ones. Turns out, the average meandering ratio of rivers approaches — you guessed it — pi.”

Perhaps what people find so alluring about pi is the fact that it is both ubiquitous and unknowable all at the same time. As mentioned above, pi shows up frequently in nature, and can be found with surprising regularity in supposedly random numbers. According to Feifei Sun of TIME, this makes pi an irresistible mathematical mystery for many people.

“What’s interesting about it is that it’s technically irrational and transcendental. The exact digits of Pi cannot ever truly be known. There’s no way for us to figure out what Pi is and that’s kind of an odd and curious thing for science. At its simplest, Pi is the measurement around the circle, divided by the measurement across the circle. The idea that something so simple should unfold in something that is unknowable is baffling.”

Pi is infinitely useful and also, apparently, infinitely unknowable. A number with this kind of contradiction begs to be remembered and respected. Does the fact that it can be found in the spiral of our DNA—in the very foundation of our genetic makeup—make us infinitely useful and unknowable as well?

This is why we care about pi, and why we think you should too. We invite you to appreciate and honor this exceptional number with us today!