Pi Day has been celebrated every year on 14th March, ever since physicist Larry Show hosted the first large-scale celebration at San Francisco's Exploratorium in 1988. However, it wasn't until March 2009 that the House of Representatives passed a resolution that officially recognised the designation of Pi Day.
As you might recall from your early school days, the mathematical constant pi is defined by the ratio of a circle's circumference to its diameter. Although pi is often shortened to 3.14, hence its celebration today, it is infinite — mathematicians have calculated it to over one trillion decimal places. As Cornell mathematics professor Steven Strogatz explained in a New Yorker essay, these digits don't show any pattern, making pi seem random. But because it always relates to a perfect circle, we see pi everywhere, including in pie itself.
For today's Doodle, Ansel baked a salted caramel apple pie, using the raw ingredients — butter, apple, cinnamon, and so on — to spell out the Google letters and depict the pi formula. Ansel also decorated his sweet creation with concentric circles to get the point across.
The French baker, who is best known for creating the cronut, a viral doughtnut-croissant hybrid, in 2013, pays homage to baking's mathematical roots in a YouTube video accompanying today's Doodle. If you've ever mistaken a teaspoon for a tablespoon, and had less than sweet results, you'll be able to relate.