Nanotechnology is one of the hot topics in science fiction.  It is used in the everyday world of the future.  It is used to cure disease, manufacture marvelous alloys, interface man and machine.  And it is used as the villain in many a tale.  The all devouring machine plague that disassembles machinery, people and worlds.  But is it really that much of a threat?  Let’s look at nanobots, assemblers and disassemblers, to see what they really are.  The little guys will probably end up looking like insects or spiders, with several little arms that end in nanoscale manipulators.  Now if the work in a fluid medium like a body they may have cilia or flippers to move through the fluids.  They will be very very small, nanoscale in fact, smaller than a bacterium, which is much smaller than a cell.  If they have any kind of energy storage it will be on a scale with them, and limited in its ability to power the robot for any length of time.  Any kind of processor on the robot will also be small, with a very limited storage facility for programs and commands.  I really don’t see them becoming independent organisms at any time in the future, unless we come up with miniaturization at an unimaginable level.  It is more likely that they would be controlled by some kind of central processing unit, and that commands would have to be sent to them through the electromagnetic spectrum.  As far as power sources go, I believe they would either have to be bathed in an electromagnetic field, have some kind of recharging station they could go to, or, in the case of nanotech within biological structures (like us) they would have to use sugars or ATP as a power source.

Actually, far from being invincible death machines, nanobots would be very fragile structures that could be destroyed in a number of ways.  They are too small to be shielded, and any strong electro-magnetic pulse would surely take them out.  Interrupting their command signal would also stop them in their tracks, or at least not allow them to move on to the next task, as they would not receive the command to move on to the next task.  And of course the use of anti-nanotech nanites that are equipped and programmed to take out other nanites, to break up the swarms.  I really believe that any civilization that has progressed past early atomic age will be able to stop them, at least by using EMP.  The threat of grey goo, where nanotech eats everything on the surface of a planet and reduces it to garbage, is not something that any civilization past exploding an atomic bomb would have to worry about.  Civilizations prior to that might have a problem, especially if they don’t know what is going on.

Now it really gets me how nanotech is portrayed in the movies, especially the made for TV variety.  Nanotech is like the Scifi version of the disintegrate spell from D&D, or the material phaser from Star Trek.  Anything attacked by a swarm of nanobots, not even a big one mind you, is taken apart within seconds.  Think of the stadium from the modern version of The Day The Earth Stood Still.  Now you see it, now it’s dust.  Living things get a fraction of a second to scream and then they’re gone.  Again to dust, so I guess all that water in the human body doesn’t really amount to much, or there would be a little solid dust and a lot of water droplets.  But would nanotech actually work this quickly?  I remember taking Anatomy and Physiology and learning that some enzymes perform their function 10,000 times a second.  This is mostly due to the tiny scale these molecules work over.  If you opened your fingers in one second, and the motion covered ten centimeters, you would be moving over a distance of ten million nanometers, or 1,000 nanometers over 10,000 times in that second.  The scale allows so many actions in such a short time.  Now let us release a swarm of killer nanobots to attack an adult human.  The nanobots, assuming they have the ability to fly, land on the human and begin disassembling.  First they have to get through the layers of skin.  Even working their fastest this is sure to take some seconds to minutes.  Instead of flying apart in a cloud of dust with seconds, we have a human with some reddening skin and some irritation.  Maybe within minutes we have enough skin shed that the little buggers are attacking capillaries and even veins and arteries.  The human us likely to bleed out well before he really starts coming apart.  If the little bugs get into the blood stream then they can be all over the body in less than a minute.  But they have the same problem working inside out as outside in.  There is a lot to disassemble.  There will be no going from healthy human to cloud of dust in seconds.  The same holds true for aircraft, ships, whatever.

Now this doesn’t mean that nanobots can’t be an effective weapon.  Just not an instantaneous disintegration swarm.  They could get into a body, infiltrate the body over a short period of time, then interrupt metabolic pathways, cutting off the transport of oxygen or the production of ATP.  They could destroy nerve pathways by taking apart neurotransmitters.  They could open veins and arteries and bleed out the victim.  They could muck up the workings of machines and electronics by disassembling the inner workings.  They could even totally destroy material objects if given time, meaning more than seconds, probably less than days.  They would still be a frightening threat in the proper situation, but not the weapon of mass destruction that sensationalist science fiction makes them to be.