**Just two more days until Tau Day 2011! **

If the Tau movement and its central tenet, that it should be tau and not pi which is foregrounded in our math curriculum, our discourse, our literature, our mathophile culture, are at all new to you, then you may be filled with doubts and objections.

Is this really worth caring about? Isn’t changing such a well-established notation totally infeasible? Won’t this just be more confusing for the children? And so on. Every objection and problem I can think of is addressed in Michael Hartl’s Tau Manifesto.

Every problem except one.

*The real unsolved problem is one of dessert.*

Vi Hart lays the problem out with mouthwatering clarity in this video. It seems like 1/2 pi radians should cover half a pie, but it doesn’t. It only covers a quarter of a pie. This captures the nonintuitive nature of pi very well (and *a fortiori* a reason why tau should be in the classroom).

But there’s a problem. No one is suggesting that we change pi to mean 6.28and-so-on. That would be horribly confusing. And I doubt we can change the meaning of the word “pie”. One solution might be to change units to double radians, or dradians. Then a pie would contain pi dradians. But remember, we have already seen that radians are the “right” units to use.

It’s a tricky problem. Here is my solution.

I propose the *taue*, a double-decker pie. (Just remember that a taue is like 2 pie, or if you’re really into this that a pie is like half a taue.) Pi radians of a taue is the rough equivalent of a whole ordinary pie (on the basis of filling, of course; valuing the crust is subtler and ignored here). Pi/4 radians (one eighth of a circle) contains a quarter of a pie in yummy fruit goodness.

It’s not obvious* a priori* that this will actually work. Will the bottom layer of filling vent properly? What will you actually bake the thing in, if you don’t have some kind of double-deep pie pan (which should be called a taue pan if it exists).

Well, I did my first official test of my proposed solutions to those problems yesterday (Saturday), and I’m here to tell you that progress tastes delicious.

- Solution to Problem #1: Use lattice crusts for the top and middle.
- Solution to Problem #2: I baked my concoction in a 10″ springform pan, because they have nice high walls.
- For the test run I used canned fillings. One can of cherry on top, one can of apple on the bottom. (Each layer had the amount of filling I’d ordinarily use in an 8″ or 9″ pie.)
- My crust was made from 3 3/4 cups of flour (I’m partial to King Arthur whole wheat), 3/4 C of ice water, 3/4 tsp salt, and 1 1/2 cups of organic salted butter, in the “usual” way. Mix the dry, dice and cut in the butter, and add the water a little at a time
- I divided the dough into three balls (proportioned roughly 2:1:1 or maybe 5:2:2) and let chill a little less than 4 hours.
- I rolled out the large ball of dough and used that to cover the bottom and sides of the pan. Then the apple layer. Then rolled out one of the small balls and made a lattice (three strips each way and two diagonals). Then the cherry layer. Then rolled out the other ball for the top lattice (five strips each way).

I wish I’d used less flour when rolling out the dough, and I could have been more careful making my lattice strips prettier, but I brought the taue to my parents’ house for tasting by myself, my wife, my parents, and my children. Success.

With the test out of the way and successful, I’ll be making at least two “official” taues this Tau Day season: one on Tau Eve and another on Tau Day proper. I’ll post pictures and recipes of those here.

P.S.

Do you have an objection or doubt not addressed in the Tau manifesto? By all means raise it here. I’ll address it if I can and forward it if I cannot.

Minor criticism: if we’re going to be using things as vague as real-life pies to argue the point, critics will no doubt say: “pi has twice as many ‘legs’ as tau, and thus, if either is going to be twice the other, pi should be twice tau, and not the other way around.” What you need is a “pi” symbol with 4 “legs”.

Ah, but no. Read the legs as Roman numerals. Then pi reads as “squiggle over 2” and tau reads as “squiggle over 1”. Quite consistent.

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