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History (and Mathematics) of Pi

On this Pi Day, besides celebrating with a piece of pecan pie, I wanted to explore the connection this mathematical enigma has with ancient science. 

Not surprisingly, the concept of Pi was known to many ancient civilizations including the Indians, Chinese, Babylonians, and Egyptians. However, its modern name and symbol came much later -- in the  1700s after William Jones introduced the symbol π and Euler popularized it.

Indians are known to be the earliest users of pi, although western texts often overlook this fact and attribute the first calculation of the value of pi to Archimedes of Syracuse around 200 BCE. However, Pi has been mentioned as early as 1500 BCE in the Hindu religious text, the Rigveda. It is believed that ancient Indians were familiar with pi even earlier, but this part of its history is largely unknown to the western scientific world.

The value of pi was approximated to be 3 by most ancient civilizations. The first person to calculate the value more accurately was Aryabhatta, an Indian mathematician and astronomer, who calculated it to be 3.1416 in 476 AD, beating Archimedes by almost 300 years. Considering the value of pi is now known to be 3.14159... , the accuracy to four decimal places is impressive. Even more astonishing is the fact that he used the word āsanna or meaning approaching in his calculation of pi, indicating that he seemingly understood that the number was not a finite number but in fact, an irrational number as is now known! Again the credit for discovering its irrationality is widely credited by westerners to European mathematician Johann Lambert in 1761, more than a millennia later.

Whatever the ancient history is, we now know the value of pi to 100 trillion digits, thanks to modern computational power. In contrast, at the start of the 20th century, only about 500 digits of pi were known.

While pi was and continues to be mostly used in geometry and in particular, in relation to a circle, the earliest practical use of pi is seen in the Egyptian pyramids. The pyramids at Giza were discovered to be built on the principles of pi. The vertical height of the pyramid is related to the perimeter of its bases by the same ratio as a circle’s radius and its circumference are related; ie. 2π. That is quite astounding, in my opinion.

Relationship between perimeter and height of the pyramid. P/H =2π

Pi also has some uses in medicine, especially in eye care. Because the eye is circular, pi is used in calculating the size and structure of the eye which then leads to tailored treatment. Surgeons also use it in calculating the catheter required to dilate a stricture by calculating its circumference. So this interesting number is now just for mathematics buffs but used in other sciences too, where any circular or cylindrical objects are used. For example, NASA regularly uses pi to calculate trajectories of space flights and communicate with satellites. It is also used to measure volume of cylindrical or spherical objects like water tanks, swimming pools etc. The link below gives five interesting engineering uses for pi by Honeywell.

https://www.honeywell.com/us/en/news/2020/03/5-ways-our-engineers-use-pi 


Sources:
https://www.britannica.com/biography/Aryabhata-I 
https://www.exploratorium.edu/pi/history-of-pi 
https://mathshrc.com/Journal/articles/a15/a15.html


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