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In chemosynthesis, the traditional (and ubiquitous in nature) method of initiating chemical reactions, many millions or more of the reactant molecules are combined in a liquid or vapor, letting them randomly collide through thermal motion until a sufficient quantity of the desired reaction products are produced. By contrast, in mechanosynthesis, an advanced chemical synthesis technique still in the development process, molecular mechanical systems operating under programmed instructions would bring together a single molecule or atom with another, bonding them together in a directed and orderly fashion. Utilizing this method, undesired reactions could be avoided, and reaction throughput could be increased considerably.
Rudimentary mechanosynthesis was already demonstrated with silicon in 2003, by Oyabu et al. Using a scanning tunneling microscope (STM), Oyabu and his collaborators used mechanical force alone to make and break covalent atomic bonds. This feat was performed under cryogenic temperatures in a vacuum environment. Earlier, in 1988, IBM researchers spelled out the letters “IBM” with xenon atoms on a copper surface. This was not true mechanosynthesis, but demonstrated the feasibility of manipulating individual atoms with an STM, a microscope implement with a monoatomic tip. In principle, manipulating individual molecules with an STM tip can be done, although automation of the process has been difficult.
For mechanosynthesis to be something other than a scientific curiosity, and be useful for building practical products, it would have to be carried out in a massively parallel fashion, making use of more flexible atomic building blocks such as carbon. To build the required number of atomic-scale manipulators for mechanosynthesis processing systems, self-replicating and general-purpose manipulators would be highly desirable. Such a device has been called a molecular assembler by the scientist who originally envisioned it, Dr. Eric Drexler. Drexler published a popular exposition on the topic in 1986, Engines of Creation, followed by the more technical Nanosystems in 1992, which outlined a range of molecular machines exploiting mechanosynthetic processes.
If a self-replicating assembler based on carbon mechanosynthesis could be developed, exponential growth from self-replication could allow kilogram quantities to be created in only a few dozen replication cycles, even if the molecular assemblers themselves only weigh a few picograms. Then, the assemblers could be directed to cooperate in constructing macro-scale products such as computers, power tools, and automobiles.
Exploiting precisely-directed atomic-level construction, these products could be built with every atom in a predetermined place. This would permit performance increases of several orders of magnitude in several areas, such as power density of motors and miniaturization of processing elements. Our current machinery is built by relatively crude processes by comparison, and tends to be relatively disorganized at the atomic level. This futuristic manufacturing methodology has been referred to as molecular nanotechnology or molecular manufacturing.