Invisibility is no longer confined to fiction. In a recent experiment, microwaves
were bent around a cylinder and returned to their original trajectories, rendering
the cylinder almost invisible at those wavelengths. This doesn't mean that we're
ready for invisible humans (or spaceships), but by using Maxwell's equations, which
are partial differential equations fundamental to electromagnetics, mathematicians
have demonstrated that in some simple cases not seeing is believing, too.

Part of this successful demonstration of invisibility is due to metamaterials
electromagnetic materials that can be made to have highly unusual properties.
Another ingredient is a mathematical transformation that stretches a point into
a ball, "cloaking" whatever is inside. This transformation was discovered while
researchers were pondering how a tumor could escape detection. Their attempts
to improve visibility eventually led to the development of equations for invisibility.
A more recent transformation creates an optical "wormhole," which tricks
electromagnetic waves into behaving as if the topology of space has changed.
We'll finish with this:

For More Information: Metamaterial Electromagnetic Cloak at Microwave Frequencies, D. Schurig et al, Science, November 10, 2006.