Still Believing in Molecular Assembly--Robert Freitas Jr. and the Diamondoid Age
LF[Anissimov]:.... What makes hydrocarbons preferable to other carbon-containing molecules, such as carbon dioxide from the atmosphere, or carbonate rocks?Much more at the source
RF: That's a very good, fundamental technical question to ask. It's true that any feedstock molecule containing carbon atoms can, in principle, be used as a source of carbon atoms for construction of diamondoid objects. But diamond is essentially a large hydrocarbon molecule, so it should not be surprising that chemically similar hydrocarbons are the most efficient precursor material.
Oxygen-rich carbon feedstock generally requires much more energy to convert to diamond than hydrogen-rich feedstock, and can also lead to significant amounts of waste products if there are lots of unused extra atoms in the feedstock. The Merkle-Freitas hydrocarbon assembler, the first zero-emissions (non-polluting) bottom-up replicator ever proposed, uses acetylene feedstock as its sole carbon and hydrogen source. Dealing with noncovalent feedstocks (e.g., ionic-bonded minerals such as calcium carbonate) presents additional complications.
....Employing saturated hydrocarbons of increasing chain length (CH4, C2H6, C3H8, ...) as feedstock also somewhat improves net reaction energy. Note that using CO2 as the carbon source costs 8 times more input energy than for natural gas (CH4) feedstock, or 20 times more input energy than for propane (C3H8). Taking apart calcium carbonate minerals such as limestone, marble, calcite, or aragonite to extract their carbon content is even less energy efficient. But if you're willing to spend the extra energy and create lots of waste products in the process, it could probably be done.
LF: What do you think are the first products that nanofactories will build?
RF: The first products will almost certainly be more nanofactories, nanofactory components and manufacturing tools, in order to ramp up total productive capacity as quickly as possible.
Once sufficient productive capacity exists, the nature of the next products to be made will be dictated by a multitude of factors such as: (1) how quickly the nanofactory can fabricate products, (2) the range of elements from which the nanofactory can fabricate products (hydrocarbons only, or other atoms?), (3) the size range of products that can be made, (4) the cost per kilogram of assembled products (early products using the first primitive nanofactories may still be extraordinarily expensive), (5) the utility of the products, (6) who's paying for the R&D and holds the patent/licensing rights (e.g., private company, NIH, university, military?), (7) how much funding is available, and so forth.
But I think a good case can be made for medical nanorobots being among the early consumer products. That's because:
(1) even relatively small (milligram/gram) quantities of medical nanorobots could be incredibly useful;
(2) nanorobots can save lives and extend the human healthspan, thus will be in high demand once available;
(3) manufacturers of such high value products (or of the nanofactories, depending on the economic model) can command a high price from healthcare providers, which means nanorobots should be worth building early, even though early-arriving nanomedical products are likely to be more expensive (in $/kg) than later-arriving products....
Most commercial and academic research efforts are oriented toward more modest goals than the universal molecular assemblers that Freitas is trying to build. But it is the "diamondoid" and quasi-diamondoid assemblers such as those that Freitas designs, that have the greatest long-term potential for both good and ill. Molecular assemblers are a disruptive technology in the most profound sense of the term.
If you have not yet read Eric Drexler's Engines of Creation, take a look at the online version available at Drexler's website.
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