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The Evolution of Nanomachinery
csy writes: "Harvard's George Whitesides has a wonderful article on Nanomachinery in this month's issue of Scientific American. He casts doubts on the Drexlerian vision of mechanical assemblers, and argues that biology and chemistry, rather than mechanical engineering point to the answers in the quest for nanomachines."
The article talks about the machinery of cells as an example of existing nano-machinery on which we should base the development of artificial nano-machines - but the proteins and other bio-molecules in a cell are actually pretty large compared to some of the things we can do even now with STM microscope tips and carbon nanotubes. Even the smallest virus is 0.05 microns across, and we're already regularly making semiconductor components on that scale. Admittedly the virus has some complex internal structure. But biology uses a very limited set of chemical elements (mainly C, H, O, N) and I think one of the main ideas with nano-machines was that there's no need to restrict yourself to the limited set of things used in biology...
Energy: time to change the picture.
A few months back Machine Design magazine did a good article on the coming of Nano technology. It's on their website at http://www.machinedesign2.com/turnstyle.php?ID=100 0... and pretty much gives a good 50,000 foot view. Only draw back is that it's in PDF again.
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While all these rods and gears and things may sound like a silly application of macro-scale approaches to micro-scale systems, it actually is all based on atomic-scale forces.
We know from experiments with various tiny-finger-type microscopes that you really can push around atoms as if they were little beach balls, and that bucky tubes really do act like fairly stiff, yet flexible, rods. They really can act mechanically on each other in reliable, predictable ways.
Nanosystems uses these interactions to argue for the possibility of nanotechnology because they are simple and easy to understand. Every argument is reinforced with large fudge-factors and cautious assumptions (for example, it is assumed that any machine will become non-functional or malfunction if a single atom is out of place).
Nobody is qualified to criticise Drexler's work until they've actually read it, and Nanosystems is the real meat of his work. It's also a great book if you'd like to learn more about any of chemistry, mechanical engineering, physics, or computer science, because of the way it ties them all together. The math is heavy going, but in its own way it is every bit as worthwhile to dig through as Knuth's TAoCP.
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You'd be surprised at the broadband connection available to things crawling around in your hair.
1) Assuming that everything is like silicon (e.g., the MEMS/stiction arguments). This is like arguing that skyscrapers are impossible based on the properties of beeswax.
2) Assuming that everything is like wet chemistry (e.g. all the comparisons to biology). He even tries to draw a dichotomy between these two.
3) General bad logic. The self-replication argument, for example, flows as follows: We don't know how to make anything that self-replicates at present; cells replicate; they do it by assembling things in a linear sequence, rather than 3d; therefore this is a serious problem for nanotech. Not only are all of these steps factually suspect (enzyme structure, for example, is very much a 3D proposition), they don't logically lead to the "conclusion".
4) Strawman arguments; saying things like "Machining and welding do not have counterparts at nanometer sizes" when no one claimed they did, or "There are no electric sockets at the nanoscale" when no one claimed there were.
This isn't exacty an objective or even rational rebuttal to Nanosystems or any of Drexler's other work; instead it seems to be an attempt at persuasion based on the author's knowledge of his own field and ignoring what Drexler actualy wrote.
-- MarkusQ