Molecular nanotechnology
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Molecular Nanotechnology (MNT) is nanotechnology using "molecular manufacturing", an anticipated technology based on positionally-controlled mechanosynthesis guided by molecular machine systems. It involves combining physical principles demonstrated by chemistry, other nanotechnologies, and the molecular machinery of life with the systems engineering principles found in modern macroscale factories. Its most well-known exposition is in the books of K. Eric Drexler.
Ralph Merkle has compared today's chemistry (in contrast to mechanosynthesis) to an attempt to build interesting Lego brick constructions while wearing boxing gloves. Because conventional chemistry has no tools that allow us to place a particular molecule in a particular place (so that it bonds in a predictable way), we must work with randomly moving molecules. As a result, when we cause a particular chemical reaction, we frequently get a mix of several different product species. We must often follow up after the reaction with a physical filtering process to extract the species we actually wanted, with the other species discarded as waste. Nanotechnology could therefore offer much cleaner manufacturing processes than today's bulk technology offers.
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Foresights
Confused terminology
Drexler has noted that some British writers have applied the term "nanotechnology" to microscale technologies like MEMS. This prompted Drexler to use the term "molecular nanotechnology".
Recently, the term "nanotechnology" is applied to the currently available fine-scale chemistry or materials science or molecular engineering. That would include "nanotech" suntan lotion and "nanotech" stain-resistant pants. This has prompted Drexler to use the term "zettatechnology" to refer to molecular manufacturing and its products. The "zetta" prefix is a reference to number of atoms in macro-sized product, unlike the Nano prefix for the number of subdivisions of a meter. Such a product is likely to have around a sextillion (1021) distinct atomic parts.[1] (http://nanodot.org/article.pl?sid=03/10/29/2017242)[2] (http://www.azonano.com/details.asp?ArticleID=56)
Hypothetical applications and capabilities
Smart Materials and Nanosensors
One application of nanotechnology is the development of so-called smart materials. This term refers to any sort of material designed and engineered at the nanometre scale to perform a specific task, and encompasses a wide variety of possible commercial applications. One example is materials designed to respond differently to various molecules; such a capability could lead, for example, to artificial drugs which would recognize and render inert specific viruses. Another is the idea of self-healing structures, which would repair small tears in a surface naturally in the same way as self-sealing tires or human skin; and while this technology is relatively new, it is already seeing commercial application in various engineering plastics.
A nanosensor would resemble a smart material, involving a small component within a larger machine that would react to its environment and change in some fundamental, intentional way. As a very simple example: a photosensor could passively measure the incident light and discharge its absorbed energy as electricity when the light passes above or below a specified threshold, sending a signal to a larger machine. Such a sensor would cost less and use less power than a conventional sensor, and yet function usefully in all the same applications — for example, turning on parking lot lights when it gets dark.
While smart materials and nanosensors both exemplify useful applications of nanotechnology, they pale in comparison with the complexity of the technology most popularly associated with the term: the replicating nanorobot.
Replicating Nanobots
Nanofacturing is popularly linked with the idea of swarms of coordinated nanoscale robots working together, as proposed by Drexler in his 1986 popular discussions of the subject. In theory, nanobots could construct more nanobots.
However, critics doubt the feasibility of controllable self-replicating nanobots: they cite the possibility of mutations removing any control and favoring reproduction of mutant pathogenic variations. Advocates counter that bacteria are (of necessity) evolved to evolve, while nanobot mutation can be actively prevented by common error-correcting techniques. Similar ideas are advocated in the Foresight Guidelines on Molecular Nanotechnology (http://www.foresight.org/guidelines/index.html).
Recent technical proposals for nanofactories do not include self-replicating nanobots, and recent ethical guidelines prohibit self-replication.
Medical Nanorobots
One of the most important applications of molecular nanotechnology will be medical nanorobotics or nanomedicine. The ability to design, build, and deploy large numbers of medical nanorobots will make possible the rapid elimination of disease and the reliable and relatively painless recovery from physical trauma. Medical nanorobots will also make possible the convenient correction of genetic defects, and can help to ensure a greatly expanded healthspan. More controversially, medical nanorobots could be used to augment natural human capabilities. However, mechanical medical nanodevices will not be allowed (or designed) to self-replicate inside the human body, nor will medical nanorobots have any need for self-replication themselves [3] (http://www.nanomedicine.com/NMI/2.4.2.htm#p19) since they will be manufactured exclusively in carefully regulated nanofactories.
Utility Fog
Another proposed application of nanotechnology involves utility fog [4] (http://discuss.foresight.org/~josh/Ufog.html) — in which a cloud of networked microscopic robots (simpler than assemblers) changes its shape and properties to form macroscopic objects and tools in accordance with software commands. Rather than modify the current practices of consuming material goods in different forms, utility fog would simply replace most physical objects.
Phased-Array Optics
Yet another proposed application would be phased-array optics (PAO). PAO would used the principle of phased-array millimeter technology but at optical wavelengths. This would permit the duplication of any sort of optical effect but virtually. Users could request holograms, sunrises and sunsets, or floating lasers as the mood strikes. PAO systems were described in BC Crandall's Nanotechnology: Molecular Speculations on Global Abundance in the Brian Wowk article "Phased-Array Optics".
Hypothetical social impacts
Despite the current early developmental status of nanotechnology, much concern surrounds its anticipated impact on economics and on law. Some conjecture that nanotechnology would elicit a strong public-opinion backlash, as has occurred recently around genetically modified plants and the prospect of human cloning. Whatever the exact effects, nanotechnology would probably upset existing economic structures, as it should reduce the scarcity of manufactured goods and make many more goods (such as food and health aids) manufacturable.
Most futurists and all economists believe that future citizens of a nanotechnological society would still need money, in the form of unforgeable digital cash or physical specie[5] (http://www.rfreitas.com/Nano/TangibleNanomoney.htm) (in special circumstances). They might use such money to buy goods and services that are unique, or limited within the solar system. These might include: matter, energy, information, real estate, design services, entertainment services, legal services, fame, political power, or the attention of other people to your political/religious/philosophical message. Furthermore, futurists must consider war, even between prosperous states, and non-economic goals.
Some resources will remain limited, because unique physical objects are limited (a plot of land in the real Jerusalem, mining rights to the larger near-earth asteroids) or because they depend on the goodwill of a particular person (the love of a famous person, a painting from a famous artist). Demand will always exceed supply for some things, and a political economy may continue to exist in any case. Whether the interest in these limited resources will diminish with the advent of virtual reality, where they can be easily substituted, is yet unclear, although the only reason why it might not is hypothetical irrational preference towards "real thing".
Risks
Beyond the fantasy scenarios, nanotechnology has daunting risks. It enables cheaper and more destructive conventional weapons. Also, nanotechnology permits weapons of mass destruction that self-replicate, as viruses and cancer cells do when attacking the human body. Commentators generally agree that humankind should permit self-replication only under very controlled or "inherently safe" conditions.
A fear exists that nanomechanical robots, if designed to self-replicate using naturally occurring materials (a difficult task), could consume the entire planet in their hunger for raw materials, or simply crowd out natural life, out-competing it for energy (as happened historically when blue-green algae appeared and outcompeted earlier life forms). Some commentators sometimes refer to this situation as the "grey goo" or "ecophagy" scenario. K. Eric Drexler considers an accidental "grey goo" scenario extremely unlikely. The "grey goo" scenario begs the Tree Sap Answer: what chances exist that one's car could spontaneously mutate into a wild car, run off-road and live in the forest off tree sap?
In light of these dangers, the Foresight Institute (founded by K. Eric Drexler to prepare for the arrival of future technologies) has drafted a set of guidelines [6] (http://www.foresight.org/guidelines/current.html) for the ethical development of nanotechnology. These include the banning of free-foraging self-replicating pseudo-organisms on the Earth's surface, at least, and possibly in other places.