# Pi

We all know that **Pi** (3.14159265359……) is the ratio of the circumference to the diameter of a circle. It is an irrational number with digits going on infinitely, following no specific pattern and is represented by the Greek letter ?. But what is generally not known are the other non-numerical places where Pi can be found. Though Pi is number, it doesn’t mean it can be used only Mathematics. In the list below, we will describe the other areas where Pi has found applications.

**10 Astrophysics & Astronomy **

Just as Pi is infinite it helps in studying the infinite stars in the universe. Pi was used by early astronomers to study the Earth and its rotation, as well as its orbits. Pi even helps in searching for new planets and their atmospheres (called exoplanets) outside our solar system. It has been used in calculating the density of a planet, which in turn tells us about the nature of the planet (whether it is made up of rocks or gases).

Pi has also been used in calculating the number of seconds in a year, which approximates to pi times 10 million seconds.

NASA uses Pi to calculate the trajectory of a spacecraft (pi transfer), for measuring craters, learning about the composition of asteroids. Lately Pi was also used in calculating the amount of hydrogen present in the ocean beneath the surface of Jupiter’s moon Europa. Yes, there is Pi in the sky too…

**9 Sound & Light **

As we know sound and light are made up of waves. Our primary senses of seeing and hearing are also dependent on light and sound waves. Pi is found in sine waves that is used for signal processing in sound and light waves. These sound waves have numerous applications in our day to day life. Pi can be helpful in studying the way springs bounce, pendulums swing and strings vibrate. One full sine wave is completed in two times Pi.

Another important application of these sound waves is in taking an ultrasound of a baby in the womb. It also helps in studying the behaviour of ocean waves – their frequency, wavelength and amplitude. Earthquakes can cause Tsunamis which caused huge devastation during 2004 in Asia.

Pi comes into play even when we are talking over phone, watching television or listening to the radio.

**8 Genetics **

Did you know that Pi can be found within our body? Pi is found in the most basic structure of human body – the DNA. DNA or deoxyribonucleic acid is the main constituent of chromosomes and the carrier of genetic information, which gives biological instructions making each species unique.

DNA is typically 1.8 meters long and forms the nucleus of our body cell with only 10 microns in average diameter. For our long DNA to fit in the constrained area, it wraps itself to form nucleosomes which look like a string of beads. This string is 1.5 times pi shorter than our DNA.

Another place where pi is found is in the spiral of the DNA double helix. The ladder like structure of the DNA helix is held together by Pi bonds. These Pi bonds are stacking interactions that help to keep the structure in place.

**7 Construction**

Pi plays an important role in construction and architecture. Since Pi is associated with circles, anything with curvature has Pi like pillars, wires and pipes used in construction. It can be used to get answers to questions like how much power will run through a wire with xx cross section or how much should be the size of a wire or a pillar to be used for a particular purpose.

Pi was found in the measurements of the Great Pyramid of Giza in Egypt. The vertical height of the pyramid and the perimeter of its base have the same relationship as the radius of a circle has to its circumference.

Pi has been used in the construction of arches, bridges, churches and buildings. Since the bridges and arches are semicircles, Pi helps in determining perimeter of the semicircle which in turn helps in calculating the amount of material required for construction.

**6 Probability & Statistics**

Pi is often called the magic number and computing pi is a stress test for even a computer. Not only does it help in calculations and numbers, it also appears in many fundamental equations that have nothing to do with circles.

It has lot of importance in statistics and is also widely used in analysing the probability or chance of anything happening or not happening. Pi is used by statisticians to track population dynamics and occurs in the tables of death.

Since Pi is composed of billions and trillions of digits, every possible number we can think of is hidden somewhere in Pi. It is amazing to think that any number for example our date of birth, phone number, or even bank account number can be found in Pi.

The mathematical expression for the bell curve known as normal distribution has pi in it. Normal distribution is important in statistics.

**5 Literary works **

Many people have tried to learn the digits of Pi using mnemonic techniques. They decipher the digits into words using the same number of letters. This form of constrained writing is called “Pilish”, in which the digits of the number Pi matches the length of consecutive words.

This form of writing has also been used by Alex Bellos in his book “Alex’s Adventure in Numberland”. “Contact” by Carl Sagan is a science fiction novel which was published in 1985. This novel involved communication with an extra-terrestrial life form, where Pi was used to decipher a message from them.

Lu Chao from China holds the current Guinness World record for memorizing Pi upto 67,000 decimal places. It took nearly 10 hours for an Indian to successfully recite up to 70,000 digits of Pi in March 2015. Pi has been the source of inspiration behind many literary works including books, songs and poems.

**4 Hollywood Fame**

No number has become as famous a star in Hollywood as Pi has.

Pi has been the source of inspiration for Hollywood director Darren Aronofsky. His movie “Pi” that was released in 1998, revolves around the life of a mathematician who wanted to unlock the patterns of life governed by this unique number. In 1995, “The Net” starring Sandra Bullock was released. This movie had Pi as the centre of the plot.

There is also a song inspired by the first hundred digits of Pi. This song was sung by Kate Bush in her album Aerial, which was released in 2005. Kate is known for her experimental music. Famous author Mike Keith used the first 10,000 digits of Pi to write an entire book – “Not A Wake”. Nobel Prize winner Wislawa Szymborska wrote a poem about Pi. There is also a Pi symphony which you can listen to… .

**3 Nature **

Anything which has a diameter and a circumference can have Pi applied to it. Pi can be found in the rainbow, in the moon, in the sun, in the pupil of the eye and even in a falling raindrop. We can also find this magical number in the sound of a pulsing heart or a planet orbiting a star. When people want to measure ripples emanating from a central point, they use pi. It also appears in colors.

Pi has been used to measure the sinuosity of rivers and the way a river meanders. If we measure the total length of any river in the world and divide by its straight route from its source to mouth, it averages to Pi.

We can’t see pi with our naked eye, but we are dependent on Pi. Isn’t it weird how a numerical ratio governs our life and is present in so many places in nature?

**2 Baking a Pie **

Readers will also find it interesting to know that there is a “Pi Day” which is celebrated every year on March 14^{th}. The reason is because this date roughly equals to 3.14, when written as a numerical date.

People bake pies to commemorate this day and guess what Pi will help you determine the size of your pie. The presence of Pi can be felt in our day to day life. We will find Pi giving answers to some of our most daily questions like:

If we want to paint a cylindrical object, how much paint will be required?

If we want to frost a round cake, how much icing will we need?

How much water will be needed to fill a circular swimming pool?

Even pizza boxes have to consider pi when making them.

The first 10 digits of pi: 3.141592653 was the most perfect pi time of the century on 3/14/15 at 9:26:53 a.m.

**1 Fashion & Accessories**

Many people believe that fashion is not for the geeks. But Pi has crossed the Math textbooks and entered the fashion world as well.

The famous French brand Givenchy makes cologne for sexy intelligent men called *Pi. *There are numerous other Pi-themed items like fashion accessories, clothes, t-shirts, bags, scarfs, watch, key chains and jewellery.

Other products inspired by Pi are Pi pie pans, Pi cookies, Pi cookie cutters, Pi shaped ice cube trays etc.

A number of these products are sold on the Pi day when people use/wear them to celebrate the day. There are also special sales and deals which are used to promote these products. All these fashion items and giveaways are a great way to motivate kids in learning maths. Before we wrap up, here is another geeky fact about Pi – the famous physicist Albert Einstein was born on the Pi day.

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Very informative Sneha.

Are there answers to questions which we haven’t asked yet embedded in Pi, or one of it’s derivatives? Or is it just like a law of numeric s that coincidentally contains answers because of what it is? Is it rather something special, or is it rather mundane because we know just enough about it to apply it to certain situations?

Can you recommend a good book to read that gives more insights into this fascinating number?

Thanks,

Gary Drumm