Friday, March 14, 2014

Pi: The Infinitely Irrational Number

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Today is a day to celebrate for math enthusiasts and pie lovers everywhere. Each year, March 14 marks a special date around the world because its numerical form is 3/14, and 3.14 is the most used form of the numerical constant, pi (π). And although it is commemorating a mathematical value, it is usually celebrated with delicious pies.

Pi Day is thought to have started in 1988, but the U.S. House of Representatives voted to make March 14 National Pi Day in 2009. Coincidentally, Pi Day also falls on Albert Einstein’s birthday, all the more reason to celebrate the world of science today.

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The significance of Pi

Pi is arguably the most important number in math and science. It is the ratio of the circumference of a circle to its diameter. If you measured the diameter of a circle, it would take approximately 3.14159 diameters to wrap around the same circle. The gif below shows this concept.

Pi, usually represented by the symbol π, is an irrational number, meaning that it cannot be expressed as a fraction. It is an infinite number and does not repeat the way that some fractions do. For example, 1/3 equals 0.3333… with the 3 repeating infinitely. Pi’s digits are not in any pattern, so they cannot be predicted because of their randomness.


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Pi is used mainly for geometric calculations like computing values related to spheres, circles, and ellipses. However, it is also useful in many mathematical equations in science like thermodynamics, cosmology, electromagnetism, and mechanics. This is because many aspects of physical and chemical systems are represented with components of spheres and points. Shapes of data sets can also frequently be represented graphically by components of circles, so pi is important for statistics and data analysis.

History of Pi

The earliest known approximations to 1% of pi date all the way back to 1900 BC, found in Egypt and Babylon. These approximations were found in clay tablets stating that the area of a circle can be approximated with the value (16/9)2 ≈ 3.16 treated as pi. There is also speculation that the Great Pyramid of Giza incorporated pi into its dimensions. The ratio of the perimeter to the height of the pyramid can be approximated by 2π. While some think this is evidence of knowledge of the number pi, many think that it is based on other factors.

The value of pi has been sought after since its significance in describing circles was discovered. The Greek mathematician Archimedes devised the first known algorithm to calculate it using circumscribed and inscribed polygons, shown in the picture below. He did this using the ratio of the perimeter of a polygon to its width. The more sides the polygon has, the more circular it is, and the closer the value is to pi. Using this method, Archimedes approximated pi to 3.1415 or 22/7 in 250 BC. The most digits of pi found using this method was 38 in 1630.


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The infinite series method revolutionized the calculation of pi in the 1600s. Basically, it adds the terms of an infinite sequence of numbers. Using this method, pi can be determined with greater precision than the polygon approximation. It was first discovered in about 1400 in India, but was not originally used to calculate pi.

Beginning in the computer era, pi can be calculated using infinite series to many digits with iterative algorithms. As computer memory keeps expanding, so does our knowledge of the value of pi.

Why do we care what the billionth digit of pi is?

For many calculations using pi, only knowing several digits is useful. However, knowing pi to many digits is advantageous for many reasons. There are many benefits for testing computational systems. Calculating digits of pi is useful to test supercomputers and algorithms. It also provides data to calculate math concepts because of its randomness.

Pi is an incredibly important number in science, math, and engineering. So let’s celebrate it with style today. As Pi day falls on a Friday this year, I would like to refer to today as Friday Pi Day, which calls for a cheers, and birthday celebration for Einstein.

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Thanks for reading, and cheers to your brain!

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