When is a billiard ball not a billiard ball? When mathematicians get involved and view a popular game as a model computer.

When you send a ball across a table and it hits the sides, it follows simple physical rules. However, mathematicians see a particle (the ball) whose motion can represent information, while each bounce can help guide it through a calculation.

For years, mathematicians have wondered whether billiards are capable of universal computation—in other words, whether a simple two-dimensional billiard system can run any computer program imaginable.