Modern nanotechnology, such as it is, is concerned with producing materials on an atomic scale, such as fiber made from so-called “bucky balls.” Star trek fans and other afficionados of science fiction think of nanotechnology as it may some day exist — millions of microscopic machines (referred to as “nanites” or more accurately “assemblers”) pushing around individual atoms and molecules. Part of this scenario is that the assemblers are self-replicating, meaning they copy themselves using any available materials. This leads to the grey goo problem, wherein an out-of-control replication process reduces the Earth and everything on it to a mass of replicators (which look like nothing so much as grey goo).
K. Eric Drexler, the father of nanotechnology, recently published a paper refuting the grey goo danger. Basically, he says that even if we are someday able to make assemblers, it will be very difficult to make them self-replicating and there won’t be much need to do so. In fact, he says, the danger from military applications (i.e. nanotech weapons) is much greater. The problem with Drexler’s thesis is that he’s an engineer.
I mean no disrespect. In my experience, there are two camps of nano people, each with very different ideas of how the whole “assembler” idea will play out. On the one hand, you have the engineers, who are used to working with machines, so they expect that assemblers will be some sort of machine (a bioMEM in the jargon, which stands for biological micro-electromechanical machine, or something like that). On the other hand, there are the biologists, who work with cells all day and think that assemblers will be some sort of heavily engineered cell. After all, cells are just biological machines that have been programmed by nature to carry out specific tasks. Why couldn’t we just reprogram them?
It’s this biological notion of the assembler that Drexler ignores in his paper. It’s pretty much impossible that a bacteria, no matter how much you engineered it, could rearrange individual atoms in a molecule, so the massive, planet-wide grey goo problem isn’t a concern. However, I can easily envision a scenario where a biological assembler intended to clean your arteries of cholesterol grows out of control and quickly kills the patient. The crux of the problem is that while mechanical assemblers are manufactured, biological ones are necessarily self-replicating.
To control this problem of uncontrolled growth, we need multiple ways to permanently turn off the cell’s ability to replicate itself before it is administered to the patient. One solution is to knock out the replication genes in the genome and put them on a plasmid, then we would need a way to destroy the plasmid before setting the bugs loose on someone’s arteries. The cells should also have multiple metabolic dependencies (similar to the way the dinosaurs in Jurassic Park needed lysine in their diet) as well as susceptibility to multiple antibiotics.
The scientists in Michael Crichton’s novel thought they had their creations under control by making them dependent on a dietary amino acid. This was a single point of control and a single point of failure, which nature is often very good at overcoming. That’s why our biological assemblers need multiple points of control. The Jurassic Park scientists should have realized this, but I guess they weren’t very good scientists. Fortunately, they were also fictional.
