Pi Day: How This Mathematical Constant Powers Space Missions and Cancer Research

Every March 14th, math enthusiasts celebrate Pi Day, honoring the mathematical constant that appears everywhere from NASA spacecraft calculations to cutting-edge cancer research. Scientists at UCLA explain how pi is essential for everything from designing rocket propulsion systems to developing rapid disease tests.

Mathematics enthusiasts and pie lovers come together each March 14th to honor Pi Day, marking the date that mirrors the opening three digits of the famous mathematical constant pi.

This fundamental number expresses the relationship between any circle’s circumference and its diameter, equaling roughly 3.14159 with decimal places that continue infinitely. Students typically encounter pi when computing circle areas or cylinder volumes, yet this constant appears throughout virtually every aspect of our modern world.

The annual observance began in 1988 when Larry Shaw, a physicist working at San Francisco’s Exploratorium science museum, established the tradition.

“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 he died in 2017.

What started as a modest staff gathering featuring actual pie evolved into an elaborate ceremony where hundreds of participants march around the museum’s pi monument, each person holding a different digit. Visitors frequently arrive early to secure their preferred number for the procession. According to Sharkland, one dedicated attendee with the pi symbol tattooed on her neck returns annually to lead the march carrying a pi banner.

The festivities commence at 1:59 p.m., representing pi’s subsequent three digits.

Scientists are utilizing pi in groundbreaking research across multiple fields.

For Artur Davoyan, who works in mechanical and aerospace engineering, pi appears so universally that isolating a single application proves challenging.

Pi forms 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,” said Davoyan, a professor at the University of California, Los Angeles.

Any circular object or phenomenon with cyclical patterns — including radio waves — requires pi for calculations. Even geometric shapes like squares or irregular forms can be analyzed by breaking them into increasingly smaller circles that utilize pi, Davoyan explained.

Davoyan’s current work focuses on developing advanced propulsion technologies to accelerate spacecraft journeys to distant solar system regions for data collection missions. He referenced NASA’s Voyager 1 and 2 missions, which launched in 1977 but didn’t achieve interstellar space until 2012 and 2018 respectively.

When NASA transmits signals to these distant probes, engineers must determine Earth’s precise orbital location around the sun and construct communication antennas using pi-based calculations. Scientists then employ pi again while receiving and analyzing the complex data streams transmitted back to Earth.

“Say aliens send something to us, something that we don’t know how to deal with,” Davoyan said. “So the very first thing that you would do, you would try to split it into simple functions… and turns out that when you do this operation, you will naturally have pis in it.”

Medical research also relies heavily on pi when examining microscopic fluid behavior.

Dino Di Carlo, who leads UCLA Samueli School of Engineering’s bioengineering department, conducts research involving polymer-based microscopic particles that function as miniature cellular laboratories. This technology serves as a crucial instrument for detailed cell analysis and understanding cellular composition and behavior.

Scientists apply the pi constant when calculating droplet formation, determining surface tension effects that control droplet separation, and managing the precise volumes of these microscopic containers, Di Carlo explained.

Di Carlo employs this methodology to identify antibodies — protective proteins that combat diseases — capable of interrupting communication signals from cancerous cells.

Pi calculations also prove essential when analyzing liquid movement through tubes and barriers, such as the sideways fluid flow in at-home COVID-19 testing kits.

Using these principles, Di Carlo developed a rapid Lyme disease test that produces results in 20 minutes, dramatically improving upon previous methods that required 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.”