20 hours ago
LOS ANGELES — Math enthusiasts and dessert lovers come together every March 14 to celebrate Pi Day, a date that corresponds to the first three digits of the mathematical constant pi.
Pi represents the ratio of a circle’s circumference to its diameter and is approximately 3.14159, though its digits extend infinitely. In school, it’s commonly used to calculate the area of a circle or the volume of a cylinder, but its applications are vast and touch many aspects of our world.
The holiday was established in 1988 by Larry Shaw, a physicist at the Exploratorium science museum in San Francisco.
“He had a very open and expansive view of the world and saw an opportunity with this number, mathematical concept, to invite people into the joy of mathematical learning,” said Sam Sharkland, program director of public programs at the museum, who worked with Shaw before his passing in 2017.
What began as a small staff celebration featuring pie quickly grew into a large event where hundreds of visitors march around the pi shrine, each carrying a digit. Attendees often arrive early to claim their favorite digit for the parade. One woman, who has the pi symbol tattooed on her neck, attends every year and marches near the front with a pi flag, Sharkland noted.
The celebration officially starts at 1:59 p.m., representing the next three digits of pi.
Here are some ways pi is used at the forefront of science.
Pi in outer space
In the field of mechanical and aerospace engineering, pi is so fundamental that it’s difficult to single out one specific use, said Artur Davoyan, a professor at the University of California, Los Angeles.
“Pi is part of literally every single formula that you would use to do any calculation, like for spacecraft motion, for materials and how they work, or propulsion systems,” Davoyan explained.
Anything round or with cyclical or repeating properties—such as radio waves—involves pi. Even squares or irregular shapes can be broken down into a series of progressively smaller circles and calculated using pi.
Davoyan’s research focuses on developing new propulsion systems to send spacecraft faster to the far reaches of the solar system to collect and transmit data back to Earth. He referenced NASA’s Voyager 1 and 2 missions, launched in 1977 but only reaching interstellar space in 2012 and 2018, respectively.
To communicate with these probes, NASA must precisely calculate Earth’s position in its orbit around the sun and design antennas using pi. Scientists then use pi again when receiving and decoding the complex signals sent back to Earth.
“Say aliens send something to us, something that we don’t know how to deal with,” Davoyan said. “The very first thing you would do is try to split it into simple functions... and it turns out that when you do this operation, you will naturally have pis in it.”
Tiny droplets of pi
Pi also frequently appears in the study of small fluid volumes.
Dino Di Carlo, chair of the bioengineering department at the UCLA Samueli School of Engineering, researches the creation of tiny polymer particles that act as miniature test tubes for cells. This technique is crucial for closely examining cells and understanding their functions and contents.
The constant pi is used in calculations related to forming these droplets, including surface tension and how droplets break apart, which helps researchers control their size.
Di Carlo applies this method to identify antibodies—small proteins that combat diseases—that could block signals emitted by cancer cells.
Pi is also essential in calculations involving fluid flow through tubes and barriers. For example, it plays a role in how fluid samples move slowly sideways in at-home COVID-19 tests.
Using these principles, Di Carlo developed a new Lyme disease test that delivers results in 20 minutes, a significant improvement over previous tests that took days or weeks.
“As an engineer and scientist, (pi) is just a part of life,” Di Carlo said. “Maybe I’ve taken it for granted.”
