Why is Pi 3.1415…? What if it was just 3? -anonymous

Dear Curious Readers,

It’s almost March 14. You know what that means: Pi Day, as in 3/14, or 3.14159265359 and so on.

I met up with my friend Nathan Hamlin, a mathematician and instructor here at Washington State University, to explore your question about this never-ending number.

We calculated Pi with some of my favorite items: yarn and a tuna can. You can try it at home, too.

We cut a piece of yarn that was just long enough to go around the circumference of the tuna can. Next, we straightened the yarn out and measured it with a ruler.

Then, we took a piece of yarn and laid it across the top of the tuna can. That gave us its diameter.

Then we did some division. If you try this at home and are still working on your long division, you can use a calculator.

We took the circumference and divided it by the diameter. We tried our yarn measurements again with a plate and a clock. We had to be very precise, but every time we divided the numbers, we got the same answer: about 3.14.

“Pi is part of the nature of the circle,” Hamlin said. “If the ratio was different, it wouldn’t be a circle.”

So, that makes your second question a bit tricky. If Pi wasn’t 3.1415 and so on, circles wouldn’t exist as we know them today.

I also found out there was a mathematician in Indiana who was convinced Pi was actually 3.2. He even tried to make it a law so all the students in the state would have to use that number in their math classes. Of course, it didn’t pass.

Hamlin said if Pi really were 3.2 or 3, it would mean Pi was a rational number.

Rational numbers include fractions, counting numbers, negative numbers, numbers with decimals that end (ex: 3.0374), and numbers with decimals that repeat (ex: 0.33333).

“This kind of goes back to one of the things in the ancient world, which was when math was first developed,” Hamlin said. “People thought that the world was a more rational place than it was.”

People thought the universe—and math—would be more orderly or logical than it turned out.

“There’s a story that’s told by math teachers that when the Pythagoreans discovered there was an irrational number, they were all on a ship together,” Hamlin said. “The person who figured it out, well, they threw him overboard!”

Pi is an irrational number. Unlike the rational numbers that have sections of repeating digits after the decimal, Pi’s digits look a little different. To give you an idea, here are just the first hundred digits of Pi: 3.14159265358979323846264

You can find Pi in nature, too. For example, you can find it in the pupil of our eyes or ringed splashes in ponds. Albert Einstein even found Pi in the shapes of rivers. It just so happens Pi Day falls on Einstein’s birthday, March 14. OK, he was born in 1879, not 1592.

I think I’ll celebrate math and science with a nice slice of tuna fish pie.


Dr. Universe

boogers edition

Got a science question? E-mail Dr. Wendy Sue Universe at Dr.Universe@wsu.edu. Ask Dr. Universe is a science-education project from Washington State University.