Reflections on the Symbolism of Pi Day; or, A Various History of π and Pie

If I had really gotten it together, I would have posted this earlier, when it was actually Pi Day. But sometimes my thinking lags, and the results don’t get written down until later. In any case…

I love the symbolism of Pi Day. I love it as an example of how we can take something that is so utterly rational and mathematical — the ratio between the circumference and diameter of a circle — and turn it into something so whimsical, interpretive, and symbolic. I love how we can take something so basic as a number and use it as an occasion to post pictures of a baked good on social media. Pi Day can be an educational event, a way of helping us all appreciate the importance of mathematics; but it is also an affirmation of human beings’ ability to make meaning out of something that seems to be dry, abstract fact. And it is a glorious instance of the joy of puns.

I think it’s worth stepping back for a moment to observe carefully all the different layers of meaning that have gone into the symbolism of Pi Day.

• First, we have the fact that many ancient cultures discovered a constant value for the ratio between the circumference and diameter of circles.
• From that ratio is derived a number, often rounded to 3.14 in decimal representation even though the actual number continues beyond these first three digits in a non-repeating, non-terminating series.
• Then we have the custom, apparently adopted by European mathematicians during the eighteenth century, of using the Greek letter π as a symbol of this number. It may seem odd to use a letter from the Greek alphabet to represent a number, but in fact, the Greeks did this too; they actually used the letter π to represent the number 80, although they usually wrote it as π’ to distinguish it from the more common use of π as representing a “p” sound.
• Next, we have the custom of attributing symbolic significance to marking the fourteenth day of the third month of the year (according to the modern western calendar system, at least). In the American system of writing dates, where the month precedes the day, we therefore have 3/14. Strictly speaking, it has no mathematically significant relationship to the number π at all, but so what? The fact that the same pattern of digits or numbers can be applied both to a mathematical constant and to a given date on a calendar is completely random, but its randomness need not impair its significance. We can make meaning even where none existed before.
• In turn, we have the quirk whereby the letter π is pronounced in modern English in the same way that we also pronounce the word “pie.” In modern Greek, the letter iota, or ι, which is the equivalent of our Roman-derived “i,” is pronounced as “ee,” and this is probably how the ancient Greeks pronounced it as well. But many dialects of English pronounce the letter “i” as “aye” or ai. So π becomes “pie,” or  /paɪ/ in the International Phonetic Alphabet.
• Finally, and perhaps inevitably, a connection is made between the English pronunciation of pi and the baked dish known as “pie,” so that people bake pies for Pi Day and post pictures of them on the internet.

Now, I know some readers may be thinking, “well, duh, all of this is obvious. Why did you need to explain all of these steps?” But to me, it’s not obvious. Sure, anyone who sits down to think through all of the steps behind Pi Day can probably figure out the points I’ve listed above. It may also be that someone other than me can present a more detailed history of how some of these steps happened. (Take these two Slate articles by Joseph Mazur, for instance.) But what fascinates me is how we can make leaps of meaning between such incredibly divergent systems of signification — from a numerical ratio in geometry, to a letter in an alphabet, to a date on a calendar, to a conventionalized phonetic pronunciation, to a silly pun, to a familiar element of American (and European) culinary culture. I love how this entire process starts with something so logical and mathematical and then ends up being a series of almost-absurd connections of meaning that have no overall pattern or systematic coherence. The symbolism of Pi Day is a perfect example of a kind of phenomenon that I enjoy exploring on this blog — how, when you examine the history of something, you can find that its meaning sometimes emerges or evolves in varied and unpredictable ways.

In modern scientific society, we tend to pride ourselves on rationalism. We often look down on numerology and other forms of number-symbolism; we think that numbers are just numbers, that there’s no real significance to them other than mere quantity, and we often assume that people who believe in number-symbolism — fearing the number thirteen, for example — are superstitiously looking for meaning or significance where none exists. But why should we let our rationalism get in the way of appreciating the whimsical symbolism of Pi Day? (It’s worth noting, by the way, that π is an “irrational” number by mathematical standards. The mathematical meaning of the word “irrational” differs from its more common meaning, of course; but I think that’s all the more reason to consider it a great pun.) Even the blogger Vi Hart, who has argued that π isn’t as mathematically special as some believe, still has one of her satirical anti-Pi-Day videos feature the making of pies. Every year, when Pi Day comes along, we highlight the most famous irrational number in mathematics; but for me, it’s an opportunity to celebrate the not-always-rational process of how human beings make unexpectedly meaningful connections between vastly different domains of experience.

Pi Pie, created at Delft University of Technology, applied physics, seismics and acousticS, from EnGLish Wikipedia