What is the simplest mathematical concept that does not map to a physical phenomenon? One of my colleagues argues that everything in math proves something in the physical world. For instance, he claims that the existence of math to describe fractals proves the infinite divisibility of matter (which is a non sequitur conclusion to make).
What is some simple mathematical concept that absolutely does not map to the physical world, contrary to this belief?

Points and lines are not physical objects because a point has zero volume and a line has zero thickness.
