# Q&A: Why Do We Celebrate Pi Day?

March 14 marks the annual celebration of Pi Day, a holiday that pays tribute to the mathematical constant most of us were introduced to in middle school geometry.

These days, scientists and mathematicians have calculated Pi to more than a trillion digits, but its exact nature remains a mystery that will never be solved. In mathematics, Pi is the ratio of a circle’s circumference to its diameter, but in pop culture, the Greek symbol has come to represent the unknown in its broadest terms. In honor of Pi Day, NewsFeed spoke to David Blatner, author of The Joy of Pi, to discuss the history, allure and evolution of the famous number.

(More on TIME.com: See the top 10 “troubled genius” movies)

What exactly does Pi Day celebrate?
It’s primarily a chance to have fun with the topic of math and science. And while it celebrates Pi officially, it’s more of an excuse to get excited and show the fun side of math and science.

Why does Pi remain such a fascinating topic hundreds of years after mathematicians first began using the symbol?
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.

So the mystery is part of the allure?
Yeah, we’ve gotten used to this idea that if we just calculate hard enough, we’ll be able to find an answer. And I think a lot of the 20th century was all about finding answers. We’ve forgotten to some degree that in early centuries, there was the idea of a true mystery —something that is not possible to know. And Pi reminds us that there are still mysteries out there. There are truly unknowable things.

But we’ve made quite a bit of progress in being able to define Pi.
We’re getting closer and closer but there will never be an answer. A thousand years ago, we knew a few digits of Pi. Somewhere in the 20th century, we started getting into the thousands of digits. In the past hundred years, we’ve gone from thousands to millions of digits, and now the world record is in the trillions. That’s kind of amazing.

What are the main questions scientists and mathematicians are asking about Pi these days?
We’re trying to pinpoint why Pi is like it is. Why do the digits of Pi unravel the way they do? One of the key questions is, is there a pattern to the digits? Are there more 7s than 4s? If there were some kind of pattern in Pi, it might give us a peek into some underlying nature of the universe. And that’s what a lot of mathematicians are trying to figure out right now. Is there some way of looking at Pi that gives us a better sense of the universe? Because everything is based on circles in the universe, so if we could understand those circles and Pi better, we could understand the universe better.

It’s pretty amazing that a mathematical symbol has become so prevalent in pop culture. Why is that?
In my research, I was just amazed at how many places Pi shows up from cartoons to movies. It just kept popping up. I don’t think people care so much about 3.14 and whatever—what people really care about is what Pi means. And the fascination and lure of Pi really is this sense of mystery that it points to. This idea that everybody knows about it, but nobody knows what it is. When you’re faced with the unknowable and it’s right at the heart of math and science, it just kind of tickles people.

(More on TIME.com: See the best pictures of the week)