Invisibility Cloak: Within Our Lifetimes?

Scientists around the world have been working on developing an invisibility cloak. It doesn't look like it's made of cloth, but by using the physical properties of light, it bends the visible spectrum of light around itself, making objects disappear from sight.

We see light that has been bounced off objects; objects that do not absorb yellow light look yellow to us, objects that don't absorb blue light look blue. Objects that do not absorb light at all appear to be white, and those that absorb all light are black.

To create an invisibility cloak, researchers had to find a way to neither absorb nor reflect light; instead, it had to be bent around the object in such a way that the light appearing to a viewer comes from behind the object, rather than the object itself.

In this way, the cloak -- and everything inside it -- disappears from view. Only in 2006 did physicists work out the math behind this principle. Now several teams around the world are working on the cloak's development.

In Indiana at Purdue University, the invisibility cloak uses tiny metal needles that are shaped into cones; the specific angles and lengths of each needle bends light waves around them, and everything inside this cone vanishes from sight. Light from behind the cloak is bent to the front, so that the viewer sees the objects behind the cloak rather than the cloak itself. This version is lightweight, using very little metal, and is still in development.

The limitation in this cloak, as in most invisibility cloaks, is that the design used can only bend a single wavelength of light - so you can eliminate the blue or the red or the yellow, but not the whole spectrum of colors. And colors that normally bounce off the object still do - leaving the cloak visible as a black object. The next step is to develop a way for all spectra of light to be bent around the cloak.

Still, even the single wavelength may prove useful; night vision goggles use only one wavelength, so a cloak targeted to that wavelength could be used to protect soldiers and others from being seen in the dark by night vision goggles. And because lasers use only a single wavelength, it could prevent radar sightings from targeting a cloaked object.

There are several other teams working on this concept, from Japan to Great Britain; all have seen limited results, mostly winding up with a cloak that warp the light as it goes around them. Still, even this kind of invisibility cloak can enable soldiers to hide in plain sight much more easily than the best camouflage uniform.