Some sad news for pi enthusiasts on Pi Day. Apparently, something called "tau" is becoming the hot new circle-based infinite mathematical constant:

Tau, technically, is just pi multiplied by 2, so about 6.28. But Michael Hartl, a physicist by training who's now an educational entrepreneur, considers this number a more elegant and appropriate circle constant than pi and thinks pi should be replaced by tau across the field of mathematics (with the proper factors of 2, of course)....

Hartl gets e-mails almost every day from people who are excited about his ideas and say they're "converting to tauism." But, of course, there are a lot of pi loyalists out there, too.

Why are people so passionate about whether we use tau or pi? Because the difference between them is so vast, and so consequential, that the outcome of this great mathematical battle *could change everything*:

In mathematics, diameter is rarely used, meaning the number 2 is often used in formulas involving pi. When you think of dividing a circle, you probably know that a quarter-turn is 90 degrees and a half-turn is 180 degrees. But trigonometry uses a unit called "radians," where a quarter-turn of a circle is pi/2 and a half-turn of a circle is pi, and so on -- which is confusing for new learners. Tau makes this more intuitive, says Hartl: A quarter turn of a circle is tau/4, and a half turn is tau/2.

Okay, it wouldn't change anything.