I've never been particularly worried about the threat of "grey goo" -- self-replicating nanomachines devouring everything in their path. Anything that tore apart and reassembled the physical world fast enough to be truly dangerous would likely cook itself from the heat output. But ever since the nanotechnology guru Eric Drexler mentioned the possibility in his seminal nanotech manifesto, The Engines of Creation, out of control nanoassemblers have become a staple of bad sci-fi and easily-startled doomsayers alike. Still, it's good to see that Dr. Drexler (along with Chris Phoenix from the Center for Responsible Nanotechnology) have published a paper spelling out precisely why free-range nanoassemblers, goo-making or otherwise, are simply not needed for the imminent nanotech revolution.
The article, Safe Exponential Manufacturing, will be freely available from the Institute of Physics electronic journals page until July 9. It's a PDF, and you'll have to create a free account on the site to get access to it. For those of you not interested in making that effort, this press release from CRN summarizes the argument.
Contrary to previous understanding, self-replication is unnecessary for building an efficient and effective molecular manufacturing system. Instead of building lots of tiny, complex, free-floating robots to manufacture products, it will be more practical to use simple robot arms inside desktop-size factories. A robot arm removed from such a factory would be as inert as a light bulb pulled from its socket. The factory as a whole would be no more mobile than a desktop printer and would require a supply of purified raw materials to build anything.
An obsession with obsolete science-fiction images of swarms of replicating nanobugs has diverted attention from the real issues raised by the coming revolution in molecular nanotechnologies, said Drexler.
This said, I doubt that the grey goo meme will go away. If anything, it serves as an unpleasant metaphor for the the potentially serious disruption full-bore molecular nanotechnology would unleash upon the economy, and will keep us all on our toes about potential military applications of nanoengineering (even if it's only used to produce cheap, non-replicating hardware). Still, it's good to know that, even if the meme exists, the threat doesn't.