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It鈥檚 time to kill off pi, says physicist Michael Hartl, who believes that an alternative mathematical constant will do its job better

What鈥檚 wrong with pi?听听听听听听听听

Of course, pi is not 鈥渨rong鈥� in the sense of being incorrect, it鈥檚 just a confusing and unnatural choice for the circle constant. Pi is the circumference of a circle divided by its diameter, and this definition leads to annoying factors of 2. Try explaining to a 12-year-old why the angle for an eighth of a pizza 鈥� one slice 鈥� is pi/4 instead of pi/8.

So what should replace pi?

In , which I published last year, I suggest using the Greek letter tau which is equal to 2 pi, or 6.28318鈥� instead. Tau is the ratio of a circle鈥檚 circumference to its radius, and this number occurs with astonishing frequency throughout mathematics.

If this idea is so fundamental, why haven鈥檛 we made the change before?

The paper that got the ball rolling on this, by mathematician , traces the history of pi. It鈥檚 only in the last 300 years that this convention was adopted, and I think it鈥檚 just a mistake. It鈥檚 one of those times in history when we chose the wrong convention.

And you are here to correct that mistake?

Yes. The aim of The Tau Manifesto was first and foremost to be fun, but it鈥檚 true that I would like pi to be replaced by something more sensible.

Have you had much success?

It鈥檚 definitely getting some traction among geeks. Eventually I think there is going to be a groundswell of support for it.

You are up against a formidable enemy, because pi is a popular constant鈥�

It is: there are books written about it, and people care enough to memorise tens of thousands of its digits. Google even changed its logo to honour pi on 14 March 2010 鈥� Pi Day.

Doesn鈥檛 using tau ruin equations like the formula for circular area and Euler鈥檚 identity?

Quite the opposite. As I show in The Tau Manifesto, using tau reveals underlying mathematical relationships that are obscured by using pi. In particular, the famous formula for circular area is the manifesto鈥檚 coup de gr芒ce.

Could tau exist alongside pi?

Yes. There is no need to rewrite the textbooks.

Has anyone successfully changed notation like this in the past?

In physics, there is an important quantity known as Planck鈥檚 constant, h. As quantum mechanics developed, it became clear that h-bar was more important, which is equal to h/2 pi 鈥� that鈥檚 the factor of 2 that pops up everywhere! h-bar is now the standard notation, though both are used.

People celebrate pi by eating pies on Pi Day. How can people celebrate tau?

I鈥檓 planning a Tau Day party for 28 June, and if you think that the circular baked goods on Pi Day are tasty, just wait 鈥� Tau Day has twice as much pie!