March 14th is known as Pi Day because the date 3/14 includes the first three digits of the constant represented by the Greek letter π (pi):
3.1415926535897932384626433832795028841971693993751…
For people who prefer food (and puns) to math, it’s also known as Pie Day, for obvious reasons. Unfortunately for those people, I’m gonna focus on the math first. (Sorry, guys: All things come to those who wait. You’ll get over it!)
In plain English, π (pi) represents the ratio of a circle’s circumference (c) to its diameter. And since a circle’s diameter is twice the radius (r), the formula is:
c = 2 π r
Simple, see?
For the area (a) inside a circle, it gets more complicated, but only by a little:
a = π r2
Which brings us to our first π joke/pun, because in English, that’s pronounced “Pi – r – squared” … but of course, as everyone knows, “Pie(s) are round.”
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Another thing noteworthy about March 14th – nothing to do with math – is that it’s the birthday for several great people. One is my mother-in-law (Happy Day, Dede!). Another 3/14 notable is Albert Einstein, born in 1879. I’ll let you figure out which of the two bakes better pies, and which has wilder hair.
Which brings us back to math. (Sorry, pie-lovers: Patience is a virtue!)
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The really cool thing about Einstein’s work is that – just based on the math – he predicted a whole bunch of stuff that actually turned out to be true in real life. For instance, his hypothesis that light behaves simultaneously as both wave and particle was an important step in the development of quantum theory. And the photoelectric effect, a phenomenon in which certain solids emit electrically charged particles when struck by light, helped prove his point. It also earned him the 1921 Nobel Prize in Physics.
Even cooler was his prediction that light passing through the vacuum of space actually could be bent by gravity. History.com summarizes it this way:
According to Einstein, gravitation is not a force, as Newton had argued, but a curved field in the space-time continuum, created by the presence of mass. An object of very large gravitational mass, such as the sun, would therefore appear to warp space and time around it, which could be demonstrated by observing starlight as it skirted the sun on its way to earth. In 1919, astronomers studying a solar eclipse verified earlier predictions Einstein made in the general theory of relativity. As a result, he became an overnight celebrity. Later, other predictions of general relativity, such as the probable existence of black holes, were confirmed by scientists.
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Just as the best pies are often the simplest – mine’s apple, what’s yours? – so too, the best scientific insights often can be expressed with utmost simplicity. Einstein said that matter and energy are actually just two forms of the same thing, related by the following elegant formula:
E = m c2
where “E” is energy, “m” is mass, and “c” is a constant representing the speed of light (approximately 186,000 miles per second) squared.
All this, and black holes too? How cool is THAT!
As for apple pie recipes, there are probably as many of those in the world as there are Pi-Day memes on the Internet. I leave it to you to bake one yourself.
Happy Pie Day, y’all!
As your local General Relativist, I’d like to note that Newton also considered whether light would be deflected by gravity. Both GR and Classical Mechanics predict that gravity bends light, they differ by a factor of two. The derivation of the CM prediction is less straightforward than the GR, oddly enough.
I guess I also favor apple. Or maybe strawberry-rhubarb. Or chocolate mousse. Or maybe just the one in front of me.