In conventional chemical synthesis or chemosynthesis, reactive molecules encounter one another through random thermal motion in a liquid or vapor. In mechanosynthesis, reactive molecules are attached to molecular mechanical systems, and their encounters result from mechanical motions bringing them together in planned sequences, positions, and orientations. Mechanosynthesis can avoid unwanted reactions by keeping potential reactants apart, and can strongly favor desired reactions by holding reactants together in optimal orientations for many molecular vibration times.
Mechanosynthetic systems resemble some biological mechanisms (and primitive forms of mechanosynthesis have been performed using scanning tunneling electron microscopes). So far, early molecular engineering has relied on such devices.
Broader exploitation of mechanosynthesis awaits more advanced technology for constructing molecular machine systems - including a molecular assembler or precursors thereof.
It has been suggested, notably by K. Eric Drexler, that mechanosynthesis will be fundamental to molecular manufacturing based on nanofactories capable of building macroscopic objects with atomic precision. The potential for these is disputed by some, most notably Nobel Laurate Richard Smalley, leading to a famous dispute between the two of them
In part to resolve this and related questions about the dangers of industrial accidents and runaway events equivalent to Chernobyl and Bhopal, and the more remote issue of ecophagy, grey goo and green goo (various potential disasters arising from runaway replicators, which could be built using mechanosynthesis) the UK Royal Society and UK Royal Academy of Engineering in 2003 commissioned a study to deal with these issues and larger social and ecological implications, led by mechanical engineering professor Ann Dowling. This was anticipated by some to take a strong position on these problems and potentials - and suggest any development path to a general theory of so-called mechanosynthesis.
Molecular Manufacturing is often used a synonym of 'Molecular Nanotechnology. Molecular manufacturng in general, is the art of building practical, complex machinery with sizes varying from 100 to 1 nanometers. "...The theoretical capabilities and performance of these systems have been analyzed for over fifteen years, molecular machine components are being built now, and molecular manufacturing could mature within the next ten years. When it becomes available, it will enable immensely powerful computers, abundant and high quality consumer goods, and devices able to cure diseases by repairing the body at the molecular level..." See reference 1.
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