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Happy Tau Day, everyone! Every June 28, a rogue fleet of math nerds makes its case for the abolition of arguably the most important irrational number in the world: pi. These men and women of the "tau" are adamant that pi, the ratio of circumference to diameter of a circle, should be replaced by tau, the circumference of a circle divided by the radius. They contend not that 3.14159265, the value of pi, is wrong, but that it's the wrong number to associate with a circle because "circles are more naturally defined by their radius than diameter," Michael Hartl, author of the Tau Manifesto, told CNN. So who are these math nerds and what's the intellectual underpinning of their movement? A brief review of the key players.

**Bob Palais, the godfather** By now, Tau Day has been celebrated for at least 10 years. The underpinnings of the movement came from Bob Palais, a research professor of mathematics at the University of Utah. In 2001, he wrote an essay called 'Pi Is Wrong' [pdf]. In his opening salvo against Pi, he wrote "I am not questioning its irrationality, transcendence, or numerical calculation, but the choice of the number on which we bestow a symbol conveying deep geometric significant. The proper value, which does deserve all the reverence and adulation bestowed upon the current imposter, is the number now unfortunately known as 2π."

**Michael Hartl, the leader** Physicist and entrepreneur Michael Hartl credits Palais with giving him the idea for his own treatise, the Tau Manifesto, which spawned this obsession into a movement with t-shirts and a testimonial page. Hartl told CNN that "Radians, a unit to measure angles of a circle, are confusing to new learners because of all the factors of 2. With tau, things become simpler: a half-turn of a circle is naturally ½ tau radians (it's also pi radians)."

**Michael John Blake, the meme master** With the Internet, everyone can have a movement and everyone can have holiday but that doesn't mean it's popular. Bringing some much-needed flavor to the movement (and high production value), Michael John Blake a multi-instrumentalist who famously wrote a pi song using the digits of the value, has also written an adaptation for tau.

**Kevin Houston, the convert** For any movement to thrive, it needs to persuade some members of the ancien regime to come to its side. Over in Britain, Kevin Houston, a mathematician at the University of Leeds "counts himself as a convert," reports the BBC:

"It was one of the weirdest things I'd come across, but it makes sense," he told BBC News.

"It's surprising people haven't changed before. Almost anything you can do in maths with pi you can do with tau anyway, but when it comes to using pi versus tau, tau wins - it's much more natural."

This article is from the archive of our partner *The Wire*.

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