This is not just theoretical because DARPA/MIT has already produced one foot long carbon nanotubes and should have one meter long carbon nanotubes by the end of this year or early in 2009.
Spiders suggest to us that producing high strength over density ratio invisible cables could be of great importance. In this paper we show that such invisible cables could in principle be built, thanks to carbon nanotube bundles. Theoretical strength of ~10 MPa, Young’s modulus of ~0.1 GPa and density of ~0.1 Kg/m3 are estimated. The theoretical strength over density ratio is huge, i.e. that of a single carbon nanotube; the strength of a real, thus defective, invisible cable is estimated to be ~1 MPa. Finally, we demonstrate that such cables can be easily transported in their visible state (with bunched nanotubes) and that an efficient anti-bunching controllable mechanism, involving pressure of ~1 Pa, can control the visible–invisible transition, and vice versa.
New Scientist indicates being narrower than the wavelength of light, carbno nanotubes are normally invisible - as long as they are separated by more than one wavelength
Nicola Pugno of the Polytechnic of Turin in Italy has calculated how many nanotubes would be needed to support a person, taking into account small defects that develop in the tubes during manufacture. When held 5 micrometres apart, to keep them invisible, they would form a cable only 1 centimetre in diameter weighing a mere 10 milligrams per kilometre.
Applications: better live magic shows. More effective garrots and decapitation traps. Live shows with Matrix movie like wire work.
These and keeping the carbon nanotubes invisible while very interesting and havnig uses will ultimately be cool yet trivial applications. The big applications are increasing production and lowering costs to increase the strength to weight ratio of materials used to build car, planes, buildings and other applications. Performance and efficiency can be radically increased and transform society.