## Happy Pi Day!

Posted on Saturday 14 March 2009 at 11:50 am by Jacob Aron
In Mathematics

Yes, today is Pi Day, a day for people all around the world to get together and celebrate the number π.

A pi pie, of course.

As I’ve discussed before π is an irrational number, meaning that when expressed as a decimal it goes on forever. I normally stick to 3.14 as the value for π. This explains why March 14th is designated Pi Day, as in the American date system it is 3/14. For those of us elsewhere August 22nd is perhaps a more suitable Pi Day, since 22/7 is a commonly used approximation for π.

If you think about it, π is a pretty strange concept. Why should the circumference of a circle divided by its diameter be this ethereal number that we can’t even write down? The symbol “π” is the only true way of expressing π, because any decimal representations – even this file of 1.25 million digits of π isn’t really correct – although the level of approximation is far beyond what you would ever need for practical calculations!

When I first found out about π, I wondered why we couldn’t just say it was 3. Surely, I thought, something could be done to tame this beast of a number. Indeed, in 1897 an effort was made in Indiana to legislate π in to submission, decreeing it equal to 3.2!

Such efforts are in vain. It is a truism to say “π = π” of course, but it’s a fact that we can never change. Perhaps in some strange parallel universe π = 3, but it’s hard for me to even wrap my mind around.

I guess then we’re stuck with π. It’s no bad thing really, as π can be an incredibly useful number in all sorts of calculations. It even has a starring role in my favourite, Euler’s equation. So, have a piece of pie on Pi Day, but be sure to measure the ratio of the circumference to the diameter before you tuck in. If it’s not π, something has gone wrong…

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