I was watching the following TED Talks video about using carbon nanotubes to build a space elevator: After the 12-13 minute point the speaker starts describing how very short carbon nanotubes can be pulled from a "nanotube forest" and spun together to create a very long thread. However the rupture strength is low compared to individual nanotubes. Elsewhere I've read that it is Van der Waals forces that cause carbon nanotubes to adhere to each other in a nanotube forest, allowing them to be pulled and spin into longer threads. The speaker suggests that it might not be necessary to grow nanotubes tens of thousands of kilometers long to build a space elevator, but rather that much shorter carbon nanotubes will have sufficient Van der Waals forces acting between each other to equal the tensile strength of a single carbon nanotube, allowing a sufficiently strong space elevator cable to be spun from relatively short carbon nanotubes. Can anyone tell me how to theoretically estimate the minimum length of two parallel single walled carbon nanotubes such that the Van der Waals forces between them are equal to the tensile strength of one?