## Historical Entry—Monday, June 28, 2010

In 2010, Michael Hartl published his paper, *The Tau Manifesto*, which proposed that the scientific community completely replace the current circle constant with tau (τ) instead of pi (π). The currently used circle constant is π ≡ C/D=3.14159265…(1).

However, the article “π Is Wrong!” (Bob Palais, *The Mathematical Intelligencer*, Volume 23, Number 3, 2001), suggested that π isn’t a rational for the circle constant. The current circle constant, he stated, uses diameter for the measurement. But when the area of the circle (A=πr^2) is measured, the radius is the measurement. He asked if the circle's diameter is important, shouldn’t the area equation be A=(πD^2)/4. Palais suggested instead using a different constant, τ ≡ C/r=6.283…. This would match mathematically with the area formula, relying on the radius as the primary measurement within both equations.

A new constant, after all this time? Mathematicians weren’t sure of the need.

Hartl expanded further on this concept in his manifesto. In the illustration above, he shows how the angles are easily notated in a manner consistent with how many people think of portions of a circle. Instead of the 90° point, or one-quarter of the circle, being rendered as π/2, with τ it becomes τ/4. This is nearly the same as using 1/4 to notate a quarter. With τ, the same is true of the half mark (τ/2), three-quarters mark (3τ/4) or even one-eighth (τ/8). This stems from the mathematical fact that a full circumference equals τ.

Though it has not been fully embraced by the scientific community as the replacement for π, it is making inroads. One of the most notable was that in 2012, MIT changed the time of their regular action admissions announcement, which occurs on __14 March (π Day)__ from 3:14 pm EDT to 6:28 pm EDT to embrace τ. In computers, the constant has been introduced in programming since it simplifies many input/output algorithms by using a less irrational mathematical notation.

The tradition of using π to describe the circle constant will be hard to overcome. It took nearly 40 years from its introduction for π to be accepted. That was over 400 years ago. In this, τ faces an uphill battle.

No matter, we can still celebrate the day. Because if one slice of π is tasty, two slices of π, or a single τ of pie, must be better.

(1) ≡ mathematical symbol for “defined as”

Tau Day

Historical Event

2010

This Day in Science Fiction History* examines notable events, real and fictional, concerning fantasy and science fiction in various media.*

Two typos need fixing here... "the area of the circle (A=π^2)" should be "the area of the circle (A=πr^2)" and

"shouldn’t the area equation be A=(πD^2)/." should be "shouldn’t the area equation be A=(πD^2)/4?"

Thank you for your kind attention....