When asked, many students answer it as 22/7, 3.14, or as a constant.
So, let’s ask, why is it 22/7 and not, say 22/8? Who defined it? The teacher who is teaching the class or some old scientist? And just because they said so, do we believe it? Or do we come up with our own definition for this Pi?
Also, why is it a constant? Also, why do some people refer to it as a universal constant? What do we mean by ‘universal’ constant? Does it mean that if an alien on a planet in a faraway galaxy were to measure for Pi, he would get the same value?
Pi is indeed a universal constant. It is not defined by your teacher or an old scientist. It is defined as the ratio of circumference of a circle to its diameter. [To those who are not familiar with the word ‘circumference’ it is the length of the circle if it was cut and laid straight on a flat surface]
And it was discovered that no matter how big or small the circle is, the ratio between its circumference and the diameter is always the same. Now, if a kid in India were measure this, or if a kid in Germany were to measure this, or if an alien in the faraway galaxy were to measure this, it would always come to the same freaking constant number, never changing.
That’s why it is called an universal constant. The first time it was discovered, the mathematicians must have felt like they touched God. Here is one number which is defined forever, for all times to come, no matter where you lived in the universe, or which species you were. The ratio of the circumference of a circle to its diameter is always the same. And we call it Pi. And roughly it happens to be equal to 22/7 or 3.14159 26535 89793 23846 26433 83279 50288 41971 69399 37510 58209 74944 59230 78164 06286 20899 86280 34825 34211 70679…
The last three dots tell you that we have still not figured out its exact value and that it is an irrational number.