Tau Day: Why You Should Eat Twice The Pie

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(CNN) — Earlier this year, the admissions office of the Massachusetts Institute of Technology related an odd tale of a conflict over, of all things, a number.

They described “two warring peoples: the people of Pi, and the people of Tau,” and proposed a compromise between the supporters of pi (the number 3.14…) and tau (the number 6.28…). As in previous years, MIT would announce its admissions decisions on 3/14, or “Pi Day,” but this year they would also acknowledge adherents of tau by sending out their decisions at 6:28, or “Tau Time.”

It was a noble attempt to broker a peace – and yet, the two tribes fight on. The truth is it’s mostly my fault. Here’s how it all happened.

A few years ago, I noticed that references to a delightful little paper called “Pi Is Wrong!” were popping up regularly on social news sites such as Hacker News and reddit.

In “Pi Is Wrong!”, mathematician Robert Palais makes the startling claim that there is something deeply wrong with π (pi), the ratio of a circle’s circumference to its diameter, a number whose importance is taught to every schoolchild and which has reached almost cult-like status in the world of mathematics. The more important number, Palais argues, is actually the ratio of the circumference to the radius, which he calls “one turn.” Because the diameter is twice the radius, this number is simply twice pi: 2 * 3.14… = 6.28…

Unfortunately, even almost a decade after the publication of Palais’ paper, the idea that pi is wrong didn’t seem to be going anywhere.

I perceived the opportunity to remedy the situation with a carefully designed social hack. All that was needed, I thought, was a convenient name and a compelling narrative, together with a new mathematical holiday to serve as a focus for the movement. Inspired by the root of the English word “turn” (τóρνoς), I chose the Greek letter τ (tau) for the number 6.28. The result, called “The Tau Manifesto,” launched on Tau Day (6/28), 2010, and immediately struck a chord (sometimes literally).

The manifesto and its companion holiday became one of those quirky stories that people of a certain mathematical bent just couldn’t help but share with their friends. The resulting “tauist movement” attracted international media attention, influenced MIT’s aforementioned admissions announcements, and inspired seventh-grader Ethan Brown to set a world record by memorizing and reciting 2,000 digits of this previously unsung mathematical constant. It even provoked a corresponding (and, in my view, unconvincing) “Pi Manifesto.”

As with so many ideas whose time has come, this one was not mine alone.

In the wake of the manifesto’s publication, I learned that physicist Peter Harremöes independently proposed using the letter tau to Bob Palais just around the same time that I notified Bob about the impending publication of “The Tau Manifesto.” We then found out that Joseph Lindenberg proposed using τ in an unpublished manuscript way back in 1992! Indeed, Peter Harremöes has discovered that Persian mathematician Jamshid al-Kashi used the number (but not the notation) as early as the 15th century, and thus proposes calling tau “al-Kashi’s constant.”

We’ve seen now how the battle between pi and tau began. How then might it end?

There are many who, although sympathetic to the cause, believe that tau can’t possibly succeed in defeating pi. I am cautiously optimistic: my work and the work of other prominent tauists (such as Vi Hart and Kevin Houston, in addition to the others mentioned above) have certainly laid the foundation for eventual victory.

In particular, the large number of enthusiastic young tauists (including a high-school robotics team named “The Tau Manifesto”) gives me hope. In addition, tau has the truth on its side: a circle is defined by its radius, not by its diameter, so dividing the circumference by twice the radius introduces an ugly factor of two into the equations of science and mathematics.

As G. H. Hardy wrote in A Mathematician’s Apology, “Beauty is the first test: there is no permanent place in the world for ugly mathematics.”

Nevertheless, I concede that the doubters may well be right. There is a powerful conspiracy, centuries old, dedicated to propagating pro-pi propaganda.

Official textbooks still use pi, and academic mathematicians, though sometimes confessing their support in private, have been apathetic or even hostile in public. But these considerations are ultimately beside the point.

The demise of pi would would be but the icing on the cake (so to speak), because “The Tau Manifesto” has already succeeded. Its principal goal was to hack geek culture, and there’s no denying that this goal has been achieved. Moreover, even if it had failed to find an audience, “The Tau Manifesto” would still have been worth writing, and not just because I would have learned from my failure. Simply put, it gave me joy to get tau out of my head and into the world. It has been my tremendous good fortune to discover that this joy is shared by so many.

So, to all the tauists of the world, I say: Thanks for your support. And Happy Tau Day!

By Michael Hartl – Special to CNN

Editor’s note: Michael Hartl is the founder of Tau Day and author of The Tau Manifesto. He is also the author of the Ruby on Rails Tutorial, the leading introduction to web development with Ruby on Rails. Previously, he taught theoretical and computational physics at the California Institute of Technology, where he received the Caltech Lifetime Achievement Award for Excellence in Teaching.

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