A molecular assembler is a molecular machine capable of assembling other molecules given instructions, energy, and a supply of smaller "building block" molecules to work from. They can work individually as tiny stand-alone systems, or potentially be organized in large numbers to form a desktop-scale nanofactory able to build macroscopic products. Distinction is sometimes made between synthetic and naturally occurring molecular assemblers.
In cellular biology, the ribosome demonstrates the essential principles of a molecular assembler. Working within a cell's environment, it reads strands of mRNA as its instructions and assembles specific large protein molecules out of more fundamental parts.
Synthetic assemblers have not yet been constructed, and some controversy exists as to whether they are possible or what their ecological impact might be. The potential uses of synthetic assemblers could be more general, and are thought to be especially applicable to materials science.
There are two entwined controversies surrounding the creation of artificial or synthetic molecular assemblers. The first is whether they can be built or even exist. Secondarily, if they can be built, then what is the potential ecological impact and the what are the appropriate political or regulatory responses.
Professor Richard Smalley, a researcher in the field of nanotechnology, takes the position that any non-natural assembler is impossible, while naturally-evolved ribosomes are the only possible realization. His opinion may be considered to be one of carbon chauvinism. On the other hand, K. Eric Drexler, founder of the Foresight Institute, asserts that such general assemblers are inevitable.
Nonetheless, within the United States, the National Nanotechnology Initiative and the Texas Nanotechnology Initiative (TNI) are proceeding with research. Both initiatives have close ties to the US military-industrial complex, and are presumedly seeking to do molecular engineering of advanced materials for military use. Currently there are no regulations governing such research, and like many military projects, there is little if any outside observation or oversight.
This lack of regulation and scrutiny has alarmed some observers, including Greenpeace and the Foresight Institute. The fear is that the developed technology could pose a serious ecological threat to life, and accordingly they advocate strong controls. Drexler of the Foresight Institute and others state that artifically created molecular assemblers could be used to build more dangerous devices that represent a clear competitive threat to all natural life.
The suggested danger to life could arise in the form of grey goo which consumes carbon to make more of itself. If unchecked such mechanical replication could potentially consume whole ecoregions or the whole Earth (ecophagy), or it could simply outcompete other natural lifeforms for necessary resources such as carbon, ATP, or UV light (which some nanomotor examples run on). Another more likely dangerous form is green goo, which co-opts a natural biologically-evolved infrastructure, as a virus or prion does, as it replicates. Accordingly, Drexler advocates quite strict guidelines, including the prohibition of the creation of any such "replicator" in Earth's biosphere.
Professor Smalley argues that regulations are unnecessary, since such replicators are supposedly impossible to construct. Both he and the TNI advocate a regulations-free environment. This position is predictably met with some suspicion given the secret and military nature of their research.
The UK Royal Society and UK Royal Academy of Engineering have commissioned a study to deal with the molecular assembler questions and related issues along with their larger social and ecological implications. The study is led by mechanical engineering professor Ann Dowling. Its report is widely anticipated to take a strong position on these problems.
"Molecular assemblers" have been confused with self-replicating machines. To produce a practical quantity of a desired product, the nanoscale size of a typical science fiction universal molecular assembler requires an extremely large number of such devices. However, a single such theoretical molecular assembler might be programmed to self-replicate, constructing many copies of itself. This would allow an exponential rate of production. Then after sufficient quantities of the molecular assemblers were available, they would then be re-programmed for production of the desired product. However, if self-replication of molecular assemblers were not restrained then it might lead to competition with naturally occurring organisms. This has been called ecophagy or the grey goo problem.
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