Pi is symbolized** π** and pronounced like “pie.” It is the mathematical symbol for the number 3.14159…, which goes on indefinitely.

**π** can be calculated by taking a circle, drawn as perfectly as possible, and dividing its circumference by its diameter. If extremely careful measurements have been made, the resulting number will go on forever with no repeating pattern. Regardless of the size of the circle, the resultant number will always be the same: 3.14159… and on and on. **π** is a mathematical constant.

Many mathematicians have tried to find a repeating pattern in **π **to no avail. In fact, in 1768, the Swiss mathematician and physicist, Johann Heinrich Lambert, proved that there *cannot* be any such repeating pattern.

**π** describes the relationship of the diameter to the circumference of a circle as well as to its area and also to aspects of the sphere of which the circle is a slice. Our knowledge of **π** in connection with circles, spheres, and also angles, goes back to the ancient Greeks and Egyptians.

But **π **pops up in many other ways. **π **plays a role in calculating equations relating to probabilities, Einstein’s Theory of General Relativity, the behavior of quantum particles, and in many other applications.

Peoples of many ancient civilizations calculated with **π**: the Egyptians, Babylonians, Greeks, Chinese, and Indians.* *Pi is the 16th letter of the ancient Greek alphabet. In the 1700’s, mathematicians named the quantity that results when the circumference of a circle is divided by its diameter “pi” because it is the first letter of the ancient Greek word, *perimetros*, which meant “circumference.”

When the ancient Greek letter pi is capitalized, **Π**, it has an altogether different mathematical meaning from that of **π**.