No, really, pi is wrong: The Tau Manifesto (Tau Day, 2010)

This is not a trolling proposal, and in fact aside from centuries of convention in using pi, it is in fact very well motivated to propose this alternatively. For those without the math background to grasp the examples, the tl;du (to long, didn't understand) is that many classical mathematical objects (the ones that will be seen in any very very advanced hs level or intermediate level college math course ) would become MUCH MUCH more uniform with respect to the values that the coefficients take.

Now, ignoring pedagogical considerations, theres no reason for having this tau value, but thats being completely dishonest about how people learn and how the brain best works. Our minds are really really really sophisticated but at times silly pattern recognition engines, and any notation that makes related topics, problems and patterns look more uniform makes it just that much easier to have insight, understanding and improved problem solving skills.

the examples to pay attention to if you're rusty beyond the hs level are the ones involving:

the notation for radians with tau instead of pi (excellent because every calculation can be thought of as a fraction of the circle), and the extended example at the end involving how using tau rather than pi leads to a natural symmetry with a whole slew of formulae is also quite good.

If you don't care about pedagogical simplicity or the overhead of having a needless notational special case, this article is not important to you, but otherwise its a very good idea or at least one worth considering.

The claim that pi is wrong is a claim about pi's inconsistency and inefficiency as a matter of mathematical language design. These guys aren't dumb enough to confuse this as a claim about formal correctness. Instead, they're playfully co-opting the rhetoric of formal correctness.

It makes all sense that tau should be the number used INSTEAD of pi: It simplifies things even more. (I hope I'm not the only one tired of writing 2*pi in papers.)

But that doesn't make pi WRONG: It's defined by C/D, and the formulas make perfectly sense, even though you have to multiply by 2. Besides, it would mean a total rewrite of a lot of papers, including a lot of mathematical books.