“A mathematician is a blind man in a dark room looking for a black cat which isn't there.” This quip is variously attributed to Charles Darwin, William James, and Lord Balfour among others. Whatever the true origin, the remark contains the truism that looking for a black object in the dark is challenging, even if the object is there.
And what is the blackest known material? A recent report from the University of Michigan reveals that single-walled carbon nanotube forests fit the bill as the blackest of them all. This material is a near perfect absorber of light throughout the visible spectrum, thus preventing any detectable light reflection.
Coating an object with such carbon nanotubes would make it invisible in the nighttime because it would be indistinguishable from the background. Moreover, the object would even be invisible to radar in the daytime because the high absorptivity could be shifted into the radio frequency range and thereby prevent electromagnetic reflections back to the detector.
Is this practical?
Not quite, especially since the demonstration objects rendered invisible in the paper were just a few microns in size and only seen with a scanning electron microscope. And the high temperature and high pressure conditions used to deposit the carbon nanotube forest experimentally are too stringent for everyday use. While these nanotubes are different than the metamaterials previously developed into “invisibility cloaks,” the possibility that paints could be manufactured containing the blackest of carbon nanotubes renders all manner of imaginative additional possibilities for invisibility.
Tom Tritton is President and CEO of CHF.
On Being Invisible [Periodic Tabloid]