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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.
The possibilities, if we just can figure them out, are enormous. You can create any kind of human cell out of those, the genetic code is all in there.
Bio-informatics is probably just in the very beginning of something huge. Once we gain full understanding of the human body we have the code to life itself. It sure is a thrilling thought
Probable impossibilities are to be preferred to improbable possibilities.
Aristotele
There's room for lots of approaches, I'm sure.
I felt the author was a bit disingenuous with this quote:
"A little submarine that was to be a hunter-killer for cancer cells would have to carry on board a little diagnostic laboratory, and because that laboratory would require sampling devices and reagents and reaction chambers and analytical devices, it would cease to be little."
This is clearly a mix of humor and a rhetorical stab at the nanotech research community. That's fine for a popular magazine like SciAm, but it's not a serious analytical point. We'd be kidding ourselves to pretend that the only possible techniques for identifying cancer cells when parked before them on the nanoscale would require lab reagents and little miniature lab assistants in white coats drawn by Gary Larson.
Of course SciAm has always been a popular publication masquerading as a scholarly journal and evocative claims have long been the stock in trade.
Good one, I guess.
I'm so concerned whether they are made of organics or metal (I used to teach chemistry and physics), but I have some work for them to do right away.
Memo to future small robot type guys:
1) Clear out any hardening of the arteries that I have already developed (I'm 50 years old)
2) I hate flossing--could you do that stuff by launching from my mouthwash?
3) About that pain in my lower back? Could you head down there an do a diagnosis? I would hate to let a bone cancer get a headstart. Oh, if there is a tumor or something bad, please take care of that while you're there.
4) Say, Viagra work but it is very expensive. Could a bunch of you tools help my tool--every once and a while? But please give me warning!
5) Hey, I know that this is not so important, but the Q-Tip package says don't use them in the ear canal. Like many others I have been feeling guilty about this for years. Could you guys...you know...that waxy stuff?
6) OK up here in the macro world we have these utilities called McAffee and Norton that look for problems and then if I give the OK, they fix what they can. Well, can we work out something like this, only on your level.
7) Gee. I almost forgot being a diabetic. You guys need to fix that first.
8) And taking that anti-depression medicine Zoloft..could you do something in my brain. BUT PLEASE BE CAREFUL THERE GUYS!
Thanks,
Brent,
Your Commander-in-Chief
Help end the use of Sigs. Tomorrow
For example, Drexler focused on mechanical computers, with little rods moving back and forth. Does he think nanoscale quantum computers, driven by electricity, can never work? No, but for his book he wanted to focus on things he could be sure would work. Because nature includes little machines, he was sure you could use little machines to build things like tiny computers.
His first book, Engines of Creation, is pretty much about existance proofs. He figures you can probably make an assembler with just 150 million atoms, so then he assumes it will take a billion atoms (just to be on the safe side) for the rest of the discussion.
And in his discussion of how we will get these magic assemblers, he said that one possible route was biological: use tailored cells to make new cells that are closer to what we want, and iterate. He isn't ignoring biology, or reality.
The article is weak. Read Drexler's book instead; it's online so you can read it now for free.
Engines of Creation
steveha
lf(1): it's like ls(1) but sorts filenames by extension, tersely
Nanomachines as scaled down miniatures of human scale machines is clearly very unlikely to materialize, for exactly the same scaling reasons that prevent us from having human size single cell organisms. Fundamental relationships between mass, surface area and linear dimensions are inescapable. These relationships govern the nature of physical structures of all sizes. Clearly at nanoscale the balance has shifted from a dominance of bulk properties to surface properties that are primarily chemical in nature. Anyone trying to translate an instrumentaility to nanoscale from human scale will fail miserably if they fail to account for the basic physics of scale.
Innovative nanomachines that make use of atomic scale forces are another thing altogether. As Whitesides correctly points out, this is the realm of chemistry and biology, not the mechanics of bulk materials.
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