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# Tau Day

Tau day is here and I’m in The Times.

The article behind a paywall but is currently (9:30am BST) on the top page:

http://www.thetimes.co.uk/tto/news/

There is also a leading article which claims I am the leader of the movement! Sorry Bob and Michael!

UPDATE: 10:23BST. BBC Online article has appeared: http://www.bbc.co.uk/news/science-environment-13906169

UPDATE: 11:48BST. Daily Mail.

UPDATE: 20:11BST Fox News

You can see my new video about Tau in my previous post.

I felt I had to comment as I’ve heard this argument before and have not heard anyone come up with this counter argument.

The radius does not define a circle entirely. If I were to give you a radius on a piece of paper and said draw the corresponding circle, you would have a choice between two different circles.

radius

centre———–circumference

circumference———–centre

This means there 3 pieces of information required, the two end points of the radius, and which one is the centre.

With a diameter, there is no ambiguity and having no ambiguity is one of the cornerstone features of mathematics.

diameter

circumference———–circumference

This only requires 2 pieces of information, the two end points. The centre can be calculated by simply working out the midpoint. I currently study maths and computer science at the University of Bristol so reducing amount of information required is an important topic.

Another counter argument is the fact that because of the way pi sounds like pie, many students when first learning it think of a pie, which is very helpful when learning as is gives them something circular to visualise. I know this has nothing to do with pure mathematics but it terms of aiding students it really helps.

I know from personal experience that neither I nor any of my fellow students from GCSE up to Uni have ever complained about pi or gotten a question wrong because they forgot about the 2 in front of it.

One final point, that example in your video with the 50p doesn’t make sense to me. If you define a diameter, place a pin in the middle and spin it around, it would make a circle, not a septagon.

I am open to other ways of thinking so feel free to e-mail me with any other arguments for the use of tau.

Just read the tau manifesto fully and after much consideration I retract my opinion that we should stick we pi.

I also realised a counter point to my reducing information argument. You could simply define a circle with a centre and a length, which is a radius. This is also less information than a diameter because a diameter requires 4 numbers, two sets of coordinates, whereas this would only require 3 numbers, 1 set of coordinates and a length.

Only thing left is the pi sounding like pie argument which really isn’t much to go on. If I ever invent a popular circular dish I’ll call it tau.

In summary, lead on with tau.

P.S Still don’t understand the 50p analogy from your video.

A convert! Fantastic news.

Unfortunately, though it would make a great post, I don’t have time to do a post on curves of constant width (because I need to get back to work after all the media attention). Try these:

http://en.wikipedia.org/wiki/Curve_of_constant_width

Chris Sangwin’s page on applications

Hi, I know it’s been a while but thought you might find this interesting.

http://www.thepimanifesto.com/

It’s convincing and I’m now on the fence of the argument. If pushed I’d say pi simply because we already use it.

Hope you enjoy the read.

Some people were really upset by this tau thing! Can you believe someone is paying money (presumably their own) for the domain name thepimanifesto.com?

The real circular constant is kappa (pi/4). It’s the ratio of circumferences and areas of circle and circumscribing square, i.e. comparing like with like. So there!

Hi George! Thanks for your comment.

I’m not convinced that the circle constant should be defined by comparing a circle to a square. For me the circle constant should be defined using as naturally and with as few definitions as possible. Tau satisfies that requirement: A circle is defined using a radius and so the simplest constant is circumference/radius.