Apologies for the hyperbole in the title, but if we are to believe this BBC article on National Tau Day, pi has provoked violent anger in people

“They feel like they’ve been lied to their whole lives, so it’s amazing how many people express their displeasure with pi in the strongest possible terms – often involving profanity.

“I don’t condone any actual violence…”

So I’m nailing my colours to the mast, with suitable hyperbole, but I’m sticking with pi. I think we should save it.

The tau-ists movement is purely a notational one, something its leader, Dr Michael Hartl, openly admits.

“When I say pi is wrong, it doesn’t have any flaws in its definition – it is what you think it is, a ratio of circumference to diameter. But circles are not about diameters, they’re about radii.”

I’m not just unimpressed by the fact this is purely a nit-pick with convention, however. My concern extends to the fact that this is a somewhat limited view of pi, and it ignores the fact that using pi produces far more elegant mathematical presentation.

Hartl seems to be deeply wedded to his circumference based definition of pi.

“What you’re really doing is defining it as the ratio of the circumference to twice the radius, and that factor of two haunts you throughout mathematics.”

Well, no. How about if you use pi to find the area of a circle. Slice your circle up into sectors and place them top to tail so they approximate a rectangle, the more sectors, the better the approximation. Taken to its limit, this rectangle will be a radius in width, and half the circumference in length. The length is pi*r, in fact. But with tau that would be tau*r/2. Eww.

The factor of 1/2 you do not want to be haunted by.

Worse is to come. Pi goes beyond just measuring circles. Euler’s identity combines so beautifully five fundamental constants:

Tau, haunted by that ugly factor 1/2, ruins it.

Don’t get fooled. Say no to tau, and save pi.

Before passing judgment, I recommend reading the sections called “Euler’s identity” and “Circular area: the coup de grce” in The Tau Manifesto. (The subtitle of that second section alone should be enough to give you pause.) I urge you to keep an open mind when reading the manifesto—by the end, you might just find yourself converted to tauism…

I confess this was a knee-jerk reaction, I didn’t read your manifesto! And I am almost persuaded by the circular area coupe de grce. Almost. I can see that being very appealing to physicists 😉

I want to think a bit more about “Euler’s Identity”. Writing 1 = 1 + 0 feels a bit desperate, but you’re right, we did cheat a bit by moving the 1 over already…

Oh, the terrible dread allure of pull of tauism…

As you might have guessed from the tone of my post I really secretly love that we are having a debate about this, and that tau day has caught the media’s eye. Nice one!

I’m glad you feel the pull of the Dark Side. Sith mathematics really is where it’s at. 🙂

By the way, the whole “five most important numbers” business is numerology, not mathematics. The deeper meaning of Euler’s identity (in its tau or tau/2 form) only becomes clear through the connection to rotations in the complex plane. Seen this way, the geometric meaning of $e^{itau/2} = -1$ is perfectly clear, as is $e^{itau} = 1$.

Oh, the pull is strong.

Well, the “five most important” numbers (most

important? hmmm) is indeed a felicitous result of a deeper truth that is not destroyed by tau. But doesn’t relying on that argument undermine the whole purpose of tau-ism – that is, that tau somehow represents a neater and more pleasing notation? It seems a bit like the argument for the UK switching to drive on the right… it’s logical to standardise with the rest of the world but the in this case the rest of the world aren’t tauists, so why bother? (Yes, I know you’re going to say tau and pi can co-exists during the transition, where by contrast allowing people to drive on either side of the road would be… inadvisable.) It is fascinating to see how you can make what might seem to be a radical change from pi to tau (at least, it’s radical given how wedded we are to pi) and observe the underlying mathematics unaffected by it. A nice little experiment, but having seen that, do we still need to go through with it?On reading in more detail your manifesto the one truly persuasive argument for me is the “pi is a pedagogical disaster” line in 2.1. Though actually 2.2 is quite convincing too. And if that weren’t enough, there’s a proof by association with Matt Groening (okay, that’s a very cool video).

It’s almost midnight here in the UK, tau day is nearly over. I did my best to #savepi, but you can’t lie in the path of progress.

I am converted.

Oh, the pull is strong.

Well, the “five most important” numbers (most

important? hmmm) is indeed a felicitous result of a deeper truth that is not destroyed by tau. But doesn’t relying on that argument undermine the whole purpose of tau-ism – that is, that tau somehow represents a neater and more pleasing notation? It seems a bit like the argument for the UK switching to drive on the right… it’s logical to standardise with the rest of the world but the in this case the rest of the world aren’t tauists, so why bother? (Yes, I know you’re going to say tau and pi can co-exists during the transition, where by contrast allowing people to drive on either side of the road would be… inadvisable.) It is fascinating to see how you can make what might seem to be a radical change from pi to tau (at least, it’s radical given how wedded we are to pi) and observe the underlying mathematics unaffected by it. A nice little experiment, but having seen that, do we still need to go through with it?On reading in more detail your manifesto the one truly persuasive argument for me is the “pi is a pedagogical disaster” line in 2.1. Though actually 2.2 is quite convincing too. And if that weren’t enough, there’s a proof by association with Matt Groening (okay, that’s a very cool video).

It’s almost midnight here in the UK, tau day is nearly over. I did my best to #savepi, but you can’t lie in the path of progress.

I am converted.

Oh, the pull is strong.

Well, the “five most important” numbers (most

important? hmmm) is indeed a felicitous result of a deeper truth that is not destroyed by tau. But doesn’t relying on that argument undermine the whole purpose of tau-ism – that is, that tau somehow represents a neater and more pleasing notation? It seems a bit like the argument for the UK switching to drive on the right… it’s logical to standardise with the rest of the world but the in this case the rest of the world aren’t tauists, so why bother? (Yes, I know you’re going to say tau and pi can co-exists during the transition, where by contrast allowing people to drive on either side of the road would be… inadvisable.) It is fascinating to see how you can make what might seem to be a radical change from pi to tau (at least, it’s radical given how wedded we are to pi) and observe the underlying mathematics unaffected by it. A nice little experiment, but having seen that, do we still need to go through with it?On reading in more detail your manifesto the one truly persuasive argument for me is the “pi is a pedagogical disaster” line in 2.1. Though actually 2.2 is quite convincing too. And if that weren’t enough, there’s a proof by association with Matt Groening (okay, that’s a very cool video).

It’s almost midnight here in the UK, tau day is nearly over. I did my best to #savepi, but you can’t lie in the path of progress.

I am converted.

Oh, the pull is strong.

important? hmmm) is indeed a felicitous result of a deeper truth that is not destroyed by tau. But doesn’t relying on that argument undermine the whole purpose of tau-ism – that is, that tau somehow represents a neater and more pleasing notation? It seems a bit like the argument for the UK switching to drive on the right… it’s logical to standardise with the rest of the world but the in this case the rest of the world aren’t tauists, so why bother? (Yes, I know you’re going to say tau and pi can co-exists during the transition, where by contrast allowing people to drive on either side of the road would be… inadvisable.) It is fascinating to see how you can make what might seem to be a radical change from pi to tau (at least, it’s radical given how wedded we are to pi) and observe the underlying mathematics unaffected by it. A nice little experiment, but having seen that, do we still need to go through with it?I am converted.

Oh, the pull is strong.

important? hmmm) is indeed a felicitous result of a deeper truth that is not destroyed by tau. But doesn’t relying on that argument undermine the whole purpose of tau-ism – that is, that tau somehow represents a neater and more pleasing notation? It seems a bit like the argument for the UK switching to drive on the right… it’s logical to standardise with the rest of the world but the in this case the rest of the world aren’t tauists, so why bother? (Yes, I know you’re going to say tau and pi can co-exists during the transition, where by contrast allowing people to drive on either side of the road would be… inadvisable.) It is fascinating to see how you can make what might seem to be a radical change from pi to tau (at least, it’s radical given how wedded we are to pi) and observe the underlying mathematics unaffected by it. A nice little experiment, but having seen that, do we still need to go through with it?I am converted.

Oh, the pull is strong.

important? hmmm) is indeed a felicitous result of a deeper truth that is not destroyed by tau. But doesn’t relying on that argument undermine the whole purpose of tau-ism – that is, that tau somehow represents a neater and more pleasing notation? It seems a bit like the argument for the UK switching to drive on the right… it’s logical to standardise with the rest of the world but the in this case the rest of the world aren’t tauists, so why bother? (Yes, I know you’re going to say tau and pi can co-exists during the transition, where by contrast allowing people to drive on either side of the road would be… inadvisable.) It is fascinating to see how you can make what might seem to be a radical change from pi to tau (at least, it’s radical given how wedded we are to pi) and observe the underlying mathematics unaffected by it. A nice little experiment, but having seen that, do we still need to go through with it?I am converted.

Oh, the pull is strong.

important? hmmm) is indeed a felicitous result of a deeper truth that is not destroyed by tau. But doesn’t relying on that argument undermine the whole purpose of tau-ism – that is, that tau somehow represents a neater and more pleasing notation? It seems a bit like the argument for the UK switching to drive on the right… it’s logical to standardise with the rest of the world but the in this case the rest of the world aren’t tauists, so why bother? (Yes, I know you’re going to say tau and pi can co-exists during the transition, where by contrast allowing people to drive on either side of the road would be… inadvisable.) It is fascinating to see how you can make what might seem to be a radical change from pi to tau (at least, it’s radical given how wedded we are to pi) and observe the underlying mathematics unaffected by it. A nice little experiment, but having seen that, do we still need to go through with it?I am converted.

I have just astonished myself by agreeing. Tau is best.

Are you going to introduce tau to your students? “Let ?=2?”. It

isa great learning opportunity.We’ve started by putting the “What tau sounds like” video on our Facebook page to see what they make of it.

That is brilliant. As is the “top comment” http://t.co/g0CTyMC about the non-bijective relationship between the musical scale and counting in base 10.

I think your next step should be raising ? at exam board meetings, and asking that it be used in future papers 😉