# Pi (π) Day: Celebrating Math in Daily Life

Q&A with Associate Professor of Mathematics Cristian Lenart

Contact: Media Relations Office (518) 956-8150

Pi Day is a holiday devoted to recognizing the importance of mathematics in society. Named after the mathematical constant whose value is the ratio of the circumference to the diameter of a circle, Pi Day is commemorated on March 14 -- or 3.14 -- Pi's approximate value. Common celebrations involve discussions of mathematics over a slice of pie.

UAlbany Professor of Mathematics Cristian Lenart discusses the history of Pi and how the equation has relevance today.

Q: When did Pi first come into use in mathematics?

A: The history of Pi starts in antiquity, spanning civilizations throughout the world. The earliest documented appearances of Pi date from around 1900 B.C.; they come from Egypt and Babylonia, and both approximate Pi with about 1 percent accuracy. While Egyptologists observed that certain proportions in some of the pyramids of ancient Egypt (2500 B.C.) are close to Pi, others have argued that the Ancient Egyptians had no concept of Pi.

Archimedes (287–212 B.C.) was the first to estimate Pi rigorously by inscribing circles in regular polygons. Around A.D. 265, the Chinese mathematician Liu Hui provided a simple and rigorous algorithm to calculate Pi to any degree of accuracy, which led to the computation of the first seven decimals (the best approximation until the 14th century).

 UAlbany Associate Professor of Mathematics Cristian Lenart (Photo Mark Schmidt)

Q: Why is Pi so important in math?

A: The original application of Pi was to calculations of lengths, areas, and volumes of geometric objects such as circles, ellipses, spheres or cones. One approaches such problems today via the methods of integral calculus, which are taught in any introductory calculus course, but Pi makes an appearance in many other areas of mathematics, such as complex numbers (obtained by introducing the square root of negative 1) and functions of a complex variable, probability and statistics (for instance, in relation to the normal distribution).

Q:  How is Pi relevant to society today?

A: The calculations mentioned above are important for such fields as engineering, physics, chemistry and biology. Although not a physical constant, Pi appears routinely in equations in physics and astronomy, describing fundamental principles of the Universe, due in no small part to the relationship between the Universe and the nature of the circle.

Such principles include: Heisenberg's uncertainty principle in particle physics (stating that certain pairs of physical properties cannot be simultaneously known to arbitrarily high precision), Einstein's field equation of general relativity, Coulomb's law describing the force between two electric charges and Kepler's third law of planetary motion.

The fact that many schools around the world observe Pi Day is part of a recent more active occurrence of mathematics in popular culture, which also manifests itself through several books, movies, plays and museum exhibits. In fact, a new Museum of Mathematics is scheduled to open in New York City in 2012, and will feature exhibits and programs that stimulate inquiry, spark curiosity, and reveal to visitors the wonders of mathematics.