That is one of the authors points -- no one has done self replication on a macro scale and nanotech just assumes self replication at the molecular level
This is really a straw man argument. If you go read Drexler's blog(e.g. this series: http://metamodern.com/2009/12/19/molecular-manufacturing-whe...), he is very explicit that the path forward is studying natural self-assembly from DNA and then tearing that apart, finding how it works, and modularizing/modifying it for our own purposes. None of this appears to be a "crazy idea" or something out of humanity's reach til long after we're all dead, as this author claims
Drexler's egotistical to be sure. It doesn't make him wrong
I think it attacks a Drexler that never existed; the chapter in Nanosystems on ways forward outlined similar ideas to that more recent post. Just because the bulk of Nanosystems explores a class of systems that's easier to analyze and currently impossible to build, he wasn't ever saying "Let's try to build this class of systems! Right now!" The OP was a total caricature.
That's not really true, we self-replicate all the time (thanks mom and dad). What we don't know how to do is design things that self-replicate from scratch, but we do already have plenty of existence proofs.
Also, self-replication is actually easier at the molecular level because all the parts are perfectly regular.
And we can think too, and you can see where is AI in that moment. :)
And ducks can fly with flexible wings.
And the Sun is a thermonuclear reactor.
You can find demonstrations of this type of things everywhere, that doesn't means that we can make them work with our materials, techniques and knowledge.
Nanotech seems to my like AI, always there, at just two steps... that's the type of problems that smell to vaporware from miles.
Somebody said that the reason there is no progress in AI is that once a problem domain is understood well enough that there are working applications in it, nobody calls it AI any longer.
Now if only we could re-program women to make iPhones. The late-night trips to the gas station and gravel store because wife has another petroleum and sand-craving would totally be worth it.
We know how to train the brain of a human being to learn physics (well not always), but that doesn't means that we understand how that brain really works.
The life if full of examples of things we know how to use but that we don't understand. Sometimes it's just impossible to control that things. Think in the stock market or economics. Chemist has been studying this type of things for centuries and you can see the result: there are chemical products everywhere you look.
What the post attack is the concept of creating nanomachines that doesn't degrade (Cosmic rays! oxidation! temperature!!) and do exactly what we want.
And about the "artificial DNA", it's something so simple... Really! the problem is in the emergent properties of DNA, proteins and environmental effects, this is where you loose control. Even nature has problems with that, life forms die, had cancer...
Self-replicating nanotech is only one kind. All you really need to be able to do is build nanomachines; whether they're built by identical nanomachines or by some big contraption doesn't matter to the end result.
