Happy Pi Day!

Today is 3·14·15, corresponding to the first five digits of pi (3.1415) … a once-in-a-century coincidence! Albert Einstein would have celebrated his 136th birthday on March 14, too. It’s a great day to eat pie! Let’s all celebrate in appreciation of how important the number π is to math and science.

Pi is a non-repeating irrational, decimal number which has been calculated to 1.241 trillion positions, with no end in sight.

Pi became useful early on in designing spherical or conical shapes. The number is determined by dividing a circumference of a circle by the diameter, which gives us a constant value for all circles.

Pi is a very old number. We know that the Egyptians and the Babylonians knew about the existence of the constant ratio pi, although they didn’t know its value nearly as well as we do today. They had figured out that it was a little bigger than 3; the Babylonians had an approximation of 3 1/8 (3.125), and the Egyptians had a somewhat worse approximation of 4*(8/9)^2 (about 3.160484), which is slightly less accurate and much harder to work with. For more, see A History of Pi by Petr Beckman (Dorset Press).

The modern symbol for pi [π] was first contemporaneously used in 1706 by William Jones, who wrote:

There are various other ways of finding the Lengths or Areas of particular Curve Lines, or Planes, which may very much facilitate the Practice; as for instance, in the Circle, the Diameter is to the Circumference as 1 to (16/5 – 4/239) – 1/3(16/5^3 – 4/239^3) + … = 3.14159… = (see A History of Mathematical Notation by Florian Cajori).

Pi (rather than some other Greek letter like Alpha or Omega) was chosen as the letter to represent the number 3.141592… because the letter [π] in Greek, pronounced like our letter ‘p’, stands for ‘perimeter’.

Since it’s infinitely long, eventually, every piece of literature that’s ever been written and every sentence that can possibly be constructed in every language that has an alphabet (if we associate some binary sequences with that alphabet) can be read from decoding the digits of Pi.