In nanotechnology , self-replication is a process in which devices whose diameters are of atomic scale, on the order of nanometers, create copies of themselves. A nanometer is 10 -9 meter or a millionth of a millimeter. In order for self-replication to take place in a constructive manner, three conditions must be met.
The first requirement is that each unit be a specialized machine called a nanorobot, one of whose functions is to construct at least one copy of itself during its operational life. (Each unit should also have some other function, unless the intended purpose of the aggregate is to cause havoc by generating the mechanical equivalent of a cancerous tumor.) A hypothetical example of a constructively self-replicating nanorobot is an artificial antibody. In addition to reproducing itself, it seeks and destroys disease-causing organisms.
The second requirement is the existence of all the energy and ingredients necessary to build a certain minimum number of complete copies of the nanorobot in question. Ideally, the quantities of each ingredient should be such that they are consumed in the correct proportion. If the process is intended to be finite, then when the desired number of nanorobots has been constructed, there should be no unused quantities of any ingredient remaining.
The third requirement is that the environment be controlled so that the replication process can proceed efficiently and without malfunctions. Excessive turbulence, temperature extremes, intense radiation, or other adverse circumstances might prevent the proper functioning of the nanorobots and cause the process to falter or fail. Science-fiction writers have suggested that mutations might occur in a sophisticated self-replicating nanorobotic community, giving rise to the machine equivalent of natural selection. Such a process might be used to create a self-sustaining, evolving colony of robots on an extraterrestrial planet.