By Dave DeFusco
Earlier this year, the National Museum of Mathematics (MoMath) in New York City made Tetrasphere, an interactive exhibit created by Dr. David Sweet, an industry professor in the Katz School鈥檚 Department of Graduate Computer Science and Engineering, a permanent part of its collection. The decision marks a full-circle moment for Sweet, whose leading research inspired the exhibit.
In 1999, Sweet co-authored a paper in the journal Nature called 鈥淭opology in Chaotic Scattering,鈥 when he was a graduate student at the University of Maryland. The work looked at what happens when objects that are moving freely, such as atoms or even stars, suddenly enter a region where they bounce around chaotically before escaping back into open space鈥攁 process called chaotic scattering.
Sweet and his colleagues showed that the ways in which these objects escape are far from simple. Imagine three or more possible exit doors. The boundaries dividing the paths are so tangled that every dividing line touches all the possible exits at once. This strange structure is known as the Wada property, and it reveals just how intricate Chaos can be.
Years later, Sweet brought this idea to life for the public. In 2018, MoMath displayed his Tetrasphere in its Composite Gallery as a temporary exhibit. The Tetrasphere is made of four mirrored hemispheres packed together like a cluster of bubbles. When visitors peer inside, the mirrors reflect light over and over, creating patterns that repeat at smaller and smaller scales. The edges of these reflections form a design that closely resembles a fractal鈥攁 never-ending pattern found in nature, like the branching of trees or the spirals of seashells.
Visitors can interact with the exhibit by flipping light switches on two triangular panels. Colored lights shine through openings into the mirrored spheres, and depending on the angles, the beams bounce unpredictably. A tiny change in the angle of entry can cause the light to scatter along a completely different path, yet the result is a mesmerizing, orderly looking pattern鈥攃haotic scattering made visible.
Though it feels like magic, the exhibit is a physical model of a complex mathematical idea. Chaotic scattering is more than just a curiosity; it helps scientists understand real-world systems, from how chemicals react, to how planets move, to how electrons flow.
Sweet has had a wide-ranging career in physics, finance and technology, but for him, Tetrasphere is special. It takes abstract, technical research and turns it into something anyone can see, touch and enjoy.
鈥淢oMath鈥檚 mission, in part, is to show the beauty of mathematics,鈥 said Sweet. 鈥淭etrasphere makes Chaos physical and intuitive.鈥
