Pi Day? Please. If social media is any indicator, it was pretty clear on 3/14/16 that Pi Day had jumped the shark. If you want to show your real mathematics bona fides, it's time to get hip to Square Root Day, the brainchild of Ron Gordon. It was way back in the fall of 1981 when Gordon’s life took a serendipitous turn.

"It was early September, I was writing a check," he said, "I write September whatever, and just looked at it and said, wait a minute we’re gonna have 9/9/81.”

As a guy who studied economics and taught a little math, the sequence caught Gordon's eye. Nine times itself is 81. Or, to put it another way, nine is the square root of 81. Gordon dubbed it “square root day” and ever since has been beating the square root drum each time one comes around. There are nine "square root days" a century. The last one was 3/3/09. The next one is Monday, 4/4/16.

"Big kids like it, little kids like it, professors like it. It’s just a little math, a little smile and a little fun," said Gordon.

Fun? OK, maybe. But it also turns out the square root is hiding in plain site all around us, touching our lives in all sorts of critical ways. So says Henry Cohn, who works for Microsoft research and teaches math at MIT.

"Basically all sorts of things that are underpinnings of modern life would fall apart completely without square roots," he said.

For starters, Cohn says, without square roots, there would be no geometry. That would make it tough to build a decent house. One architect told me that square roots allow her to take a client’s imagination and turn it into a workable floor plan. And Cohn points out that, these days, geometry is often what gets us from here to there. 

"Every time you ask for directions on your cell phone you’re implicitly asking it to start computing some square roots for you and comparing them," he said.

Without square roots, Cohn says you can say goodbye to probability theory.

"We all know that life is full of randomness but it all evens out on a large scale for the most part. And the way it evens out is governed by square roots," he said.

That’s thanks, chiefly, to something called the “Central Limit Theorem,” which might sound a bit abstract, but is actually quite practical. It’s how the state knows the Powerball will make money, and why the house, in aggregate, never really loses at a casino.  

"This is what makes insurance work," said Cohn. "When you get a large enough group of people together even though bad, random things happen to some of them the fluctuations are small enough that it’s predictable and controllable."

Then there is the Root Mean Square (RMS0. This is a method of getting an average by squaring a set of numbers, calculating the mean, and than taking its square root.

"It might sound more natural to dispense with the squaring and the square root and say I’m just going to create an ordinary arithmetic average of things," said Cohn. "But the root mean square turns out to be tractable in a way that ordinary averaging just isn’t."

Are you following the election? RMS is used to calculate the margin of error in many polls. RMS helps meteorologists spot discrepancies in computer models to make a better forecast. And then there’s electricity.

John Frank, WGBH's chief engineer explained that unless you want things blowing up left and right, you have to know exactly how much power you’re putting out. With a DC current, that’s pretty easy, it’s a steady stream. But in an AC current, the power is warbling, leaping and diving all over. To really know how much power the current is truly putting out, you need to average all those warbles. Voila! RMS.

"You will know what the value truly is," said Frank. "And everything has that RMS rating on it. It’s something you don’t think about but if it wasn’t there, nothing would work right."

So, now that you know just how crucial the square root is, perhaps you want to celebrate it this Monday. If you do, Ron Gordon has some ideas for you.

"They can make a big square root sign out of people, they can serve root beer in square glasses they can do a square dance kind of thing. Just any kind of fun way to participate in the day," he said.

And, hey, if the square root’s still not your thing. Gordon has spotted another date on the calendar that he’s pretty excited about.

"It’s years away, but Trumpet Day, which is 2/2/22. And we call it Trumpet Day because it sounds out as 'toot-toot-too-too.' Trumpet day’s gonna be a lot of fun."

We’ll take a deep dive into the importance of the trumpet at a later date.