Today is “Pi Day,” the 14th day of the 3rd month (3.14). Not only that, it is “Super Pi Day,” with the rest of the date giving the next two numbers: 3.14.15. Pi is the ratio of the circumference of a circle to its diameter. Though circles are everywhere, their numeric ratios can never be exact. The mysterious number represented by the Greek letter π has been proven to be an “irrational number,” one which has an infinite number of non-repeating decimals. And, yet, the ratio has to be used in all kinds of common calculations, from figuring the area of a circle to analyzing subatomic and astronomical phenomena.
After the jump, an excerpt and a link to an essay on π and pi day by Cornell mathematicisn Tara S. Holm. Do go to the link for an account of the history of our knowledge of the concept, including a government attempt to regularize it at 3.2 by passing a law. My favorite part is how Prof. Holm is celebrating the day: Getting her family together at 9:26 and 53 seconds (the next five numbers) and eating a piece of pie.
From Tara S. Holm, Sweet, endless pi – The Washington Post:
Today is the day when the circle gets squared — or at least gets expressed with as much clarity as the calendar can provide. This day comes along once in a century. It’s 3/14/15, and those five digits signify one of the most mystical numbers in the universe.That number, of course, is the infinite sequence of pi, which is a deceptively simple idea: the ratio of a circle’s circumference to its diameter. This is the numeric expression of a perfect curve — a line endlessly looping. And as the nation pauses (or not) to celebrate Pi Day, it’s worth reflecting on the importance of this eternally hiccuping number usually expressed in a shape that looks like an end table: π. . . .
The quest to compute evermore digits of pi continues. The current record of more than 12 trillion is held by Alexander Yee and Shigeru Kondo; they had to stop in 2013 because they ran out of disk space. On the other hand, NASA assures us that 16 digits are enough to ensure that the International Space Station stays in its correct orbit. Just 39 digits allow us to compute the volume of the observable universe to the nearest atom. . . .
So stop today — a once-in-a-century Super Pi Day, as it happens — and pay tribute to this weird number so intertwined with the workings of our universe. You’ll have plenty of company. Thousands of published articles and books have pi in the title. It is a number with its own 324-page biography and 797-page source book. As for me, today at 9:26 a.m. and 53 seconds (the next five numbers in the sequence), my children will be tucking into a piece of pie.