What the Number Pi Actually Means

This morning on the way to school my son asked me what the number pi equals.

I said: 3.14.

Then he asked another question:

“Why is it called pi?”

I joked that mathematicians were probably just very angry and decided to hide inappropriate words behind a Greek letter.

But then we actually looked it up.

The symbol pi comes from the Greek word perimetros, meaning perimeter.

So I tried to explain what pi really is.

What pi is

Pi is the ratio of the circumference of a circle to its diameter.

We were already running late for school, but I wanted to show it visually.

I found a long dry vine on the way and wrapped it around a pole. That was our circumference.

Then I roughly measured the pole’s diameter.

Now we were almost running to school, and I started laying the diameter along the vine:

“This little piece,” I told him, “is basically the digits after the decimal point.”

We tried to imagine how scientists calculated pi centuries ago, before computers.

My first guess was that they simply built very large circles and measured them more and more precisely.

And that every new digit might increase the chance of error.

Later I checked how mathematicians actually did it.

Of course, it turned out they used clever formulas and long calculations instead.

But the moment stayed with me.

Sometimes we confidently explain things based on how we imagine the world works and later discover that reality is much more interesting.

The world is a fascinating place.

And I am pretty sure my son will remember what pi is after that walk to school.