People across the world are eating pies and celebrating the circle this Saturday — and this year's Pi Day is particularly special. The full date, 3/14/15, is pi to the first four places. At 9:26 a.m. and 53 seconds, you can even celebrate pi to nine places: 3.141592653.
NPR's Math Guy, Keith Devlin of Stanford University, joined Weekend Edition Saturday host Scott Simon to share a few facts about the number behind the celebrations. First, he reminds us that it's equal to a circle's circumference divided by its diameter. Then he shares some more esoteric facts:
It took millennia to prove that pi is irrational
Pi first was discovered by ancient mathematicians, but it took until the 18th century for scientists to finally prove that pi is irrational. That means it can't be expressed exactly in decimals — if you try to calculate it, you get an infinite series of digits that are random, not predictable.
The 18th-century proof, Devlin says, was related to a problem posed by the ancient Greeks: whether it was possible to draw a square with the same area as a given circle.
"The answer is no," Devlin says, "and it has to do with the degree to which the digits in the decimal expansion of pi are random."
Pi has been calculated to more than a trillion digits...