From reading Radical Abundance :

Drexler believes that not only are stable gears possible, but that every component of a modern, macroscale assembly-line can be shrunk to the nanoscale. He believes this because his calculations, and some experiments show that this works.

He believes that " Nanomachines made of stiff materials can be engineered to employ familiar kinds of moving parts, using bearings that slide, gears that mesh, and springs that stretch and compress (along with latching mechanisms, planetary gears, constant-speed couplings, four-bar linkages, chain drives, conveyor belts . . .)."

The power to do this comes from 2 sources. First of all, the "feedstock" to a nanoassembly factory always consists of the element in question bonded to other atoms, such that it's an energetically favorable reaction to bond that element to something else. Specifically, if you were building up a part made of covalently bonded carbon (diamond), the atomic intermediate proposed by Drexler is carbon dimers ( C---C ). See http://e-drexler.com/d/05/00/DC10C-mechanosynthesis.pdf

Carbon dimers are unstable, and the carbon in question would rather bond to "graphene-, nanotube-, and diamond-like solids"

The paper I linked shows a proposed tool.

Second, electrostatic electric motors would be powered by plain old DC current. These would be the driving energy to turn all the mechanical components of an MNT assembly system. Here's the first example of someone getting one to work I found by googling : http://www.nanowerk.com/spotlight/spotid=19251.php

The control circuitry and sensors for the equipment would be powered the same way.

An actual MNT factory would work like the following. A tool-tip like in the paper I linked would be part of just one machine inside this factory. The factory would have hundreds or thousands of separate "assembly lines" that would each pass molecules from station to station, and at each station a single step is perfomed on the molecule. One the molecules are "finished", these assembly lines will converge onto assembly stations. These "assembly stations" are dealing with molecules that now have hundreds of atoms in them. Nanoscale robot arms (notice we've already gone up 100x in scale, the robot arms are therefore much bigger and thicker than the previous steps, and have are integrated systems that have guidance circuitry, sensors, and everything you see in large industrial robots today) grab parts from assembly lines and place them into larger assemblies. These larger assemblies move down bigger assembly lines, with parts from hundreds of smaller sub-lines being added to them.

There's several more increases in scale, with the parts growing larger and larger. Some of these steps are programmable. The robots will follow a pattern that can be changed, so what they produce varies. However, the base assembly lines will not be programmable.

In principle, this kind of "assembly line" could produce entire sub-assemblies that are identical to the sub assemblies in this nanoscale factory. Microscale robot arms would grab these sub-assemblies and slot them into place to produce "expansion wings" of the same nanoscale factory, or produce a whole new one.

This is also how the technology would be able to produce things that it cannot already make. When the technology is mature, if someone loads a blueprint into a working MNT replication system, and that blueprint requires parts that the current system cannot manufacture, the system would be able to look up in a library the blueprints for the assembly line that does produce those parts, and automatically translate library instructions to instructions the robots in the factory will follow. Basically, before it could produce the product someone ordered, it would have to build another small factory that can produce the product. A mature, fully developed system is only a "universal replicator" because it can produce the machinery to produce the machinery to make anything.

Please note that this is many, many, many generations of technology away. I'm describing a factory the size and complexity of the biggest factories in the world today, and the "tool tip" that is described in the paper I linked is just one teensy part that might theoretically go onto the tip of one of the smallest and simplest machines in that factory.

Also note that this kind of factory must be in a perfect vacuum. The tiniest contaminant will gum it up and it will seize up.

Another constraint to note is this. In Nanosystems, Drexler computes that the speed of motion for a system that is 10 million times smaller is in fact 10 million times faster. There's a bunch of math to justify this, but basically, scale matters, and for a mechanical system, the operating rate would scale accordingly. Biological enzymes are about this quick.

This means that an MNT factory, if it used convergent assembly, could produce large, macroscale products at 10 million times the rate that a current factory can produce them. Or it could, if every single bonding step that forms a stable bond from unstable intermediates didn't release heat. That heat product is what Drexler thinks will act to "throttle" MNT factories, such that the rate you can get heat out will determine how fast the factory will run. Yes, water cooling was proposed :)

One final note : biological proteins are only being investigated as a boostrap. The eventual goal will use no biological components at all, and will not resemble biology in any way. You can mentally compare it to how silk and wood was used to make the first airplanes.

It's not clear to me what you mean by "tearing apart a planet." Are you sifting out most of the platinum and launching it into orbit? Turning it into asteroids? Rendering the atmosphere inhospitable to humans?

Because I agree that the last is obviously possible, the first probably possible, the second probably impossible without ludicrous expenditures of effort. But it's not clear to me that any of those are things which nanotechnology would be the core enabler on.

If you mean something like "reshape the planet in its image," then again I think bacteria are a good judge of feasibility- because of the feedstock issues. As well, it eventually becomes more profitable to prey on the nanomachines around you than the inert environment, and so soon we have an ecosystem a biologist would find familiar.

Jumping to another description, we could talk about "revolutionary technologies," like the Haber-Bosch process, which consumes about 1% of modern energy usage and makes agriculture and industry possible on modern scales. It's a chemical trick that extracts nitrogen from its inert state in the atmosphere and puts it into more useful forms like ammonia. Nanotech may make many tricks like that much more available and ubiquitous, but I think it will be a somewhat small addition to current biological and chemical industries, rather than a total rewriting of those fields.

That's still pretty much a revolution, a technology that could be used to tear apart planets. It just might take a bit longer than it takes in pulp sci-fi.

That looks like it's missing the point to me. As one of my physics professors put it, "we already have grey goo. It's called bacteria." If living cells are as good as it gets, and e-coli didn't tear apart the Earth, that's solid evidence that nanosystems won't tear apart the Earth.

I suppose the Less Wrong response to this argument would be: how many of them are signed up for cryonics?

LessWrongers, and high-karma LessWrongers, on average seem to think cryonics won't work, with mean odds of 5:1 or more against cryonics (although the fact that they expect it to fail doesn't stop an inordinate proportion from trying it for the expected value).

On the other hand, if mice or human organs were cryopreserved and revived without brain damage or loss of viability, people would probably become a lot more (explicitly and emotionally) confident that there is no severe irreversible information loss. Much less impressive demonstrations have been enough to create huge demand to enlist in clinical trials before.

Technically the blindfold was intended to refer to the fact that you can't make measurements on the system while you're shaking the box because your measuring device will tend to perturb the atoms you're manipulating.

The walls of the box that you're using to push the legos around was intended to refer to our ability to only manipulate atoms using clumsy tools and several layers of indirection, but we're basically on the same page.

Nothing like it? Map the atoms to individual pieces of legos, their configuration relative to each other (i.e. lining up the pegs and the holes) was intended to capture the directionality of covalent bonds. We capture forces and torques well since smaller legos tend to be easier to move, but harder to separate than larger legos. The shaking represents acting on the system via some therodynamic force. Gravity represents a tendency of things to settle into some local ground state that your shaking will have to push them away from. I think it does a pretty good job capturing some of the problems with entropy and exerted forces producing random thermal vibrations since those things are true at all length scales. The blindfold is because you aren't Laplace's demon, and you can't really measure individual chemical reactions while they're happening.

If anything, the lego system has too few degrees of freedom, and doesn't capture the massiveness of the problem you're dealing with because we can't imagine a mol of lego pieces.

I try not to just throw out analogies willy-nilly. I really think that the problem of MNT is the problem of keeping track of an enormous number of pieces and interactions, and pushing them in very careful ways. I think that trying to shake a box of lego is a very reasonable human-friendly approximation of what's going on at the nanoscale. I think my example doesn't do a good job describing the varying strengths or types of molecular bonds, nor does it capture bond stretching or deformation in a meaningful way, but on the whole I think that saying it's nothing like the problem of MNT is a bit too strong a statement.

Life is a wonderful example of self-assembling molecular nanotechnology, and as such gives you a template of the sorts of things that are actually possible (as opposed to Drexlerian ideas). That is to say, everything is built from a few dozen stereotyped monomers assembled into polymers (rather than arranging atoms arbitrarily), there are errors at every step of the way from mutations to misincorporation of amino acids in proteins so everything must be robust to small problems (seriously, like 10% of the large proteins in your body have an amino acid out of place as opposed to being built with atomic precision and they can be altered and damaged over time), it uses a lot of energy via a metabolism to maintain itself in the face of the world and its own chemical instability (often more energy than is embodied in the chemical bonds of the structure itself over a relatively short time if it's doing anything interesting and for that matter building it requires much more energy than is actually embodied), you have many discrete medium-sized molecules moving around and interacting in aqueous solution (rather than much in the way of solid-state action) and on scales larger than viruses or protein crystals everything is built more or less according to a recipe of interacting forces and emergent behavior (rather than having something like a digital blueprint).

So yeah, remarkable things are possible, most likely even including things that naturally-evolved life does not do now. But there are limits and it probably does not resemble the sorts of things described in "Nanosystems" and its ilk at all.

Thanks for the hardware info.

An autonomous killing drone system would save soldier's lives and kill fewer civilians.

In the short-term... What do you think about the threat they pose to democracy?

drawbacks include high cost to develop and maintain

Do you happen to know how many humans need to be employed for a given quantity of these weapons to be produced?

Let's talk actual hardware.

Here's a practical, autonomous kill system that is possibly feasible with current technology. A network of drone helicopters armed with rifles and sensors that can detect the muzzle flashes, sound, and in some cases projectiles of an AK-47 being fired.

Sort of this aircraft : http://en.wikipedia.org/wiki/Autonomous_Rotorcraft_Sniper_System

Combined with sensors based on this patent : http://www.google.com/patents/US5686889

http://en.wikipedia.org/wiki/Gunfire_locator

and this one http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=1396471&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F9608%2F30354%2F01396471

The hardware and software would be optimized for detecting AK-47 fire, though it would be able to detect most firearms. Some of these sensors work best if multiple platforms armed with the same sensor are spread out in space, so there would need to be several of these drones hovering overhead for maximum effectiveness.

How would this system be used? Whenever a group of soldiers leaves the post, they would all have to wear blue force trackers that clearly mark them as friendly. When they are at risk for attack, a swarm of drones follows them overhead. If someone fires at them, the following autonomous kill decision is made

if( SystemIsArmed && EventSmallArmsFire && NearestBlueForceTracker > X meters && ProbableError < Y meters) ShootBack();

Sure, a system like this might make mistakes. However, here's the state of the art method used today :

http://www.youtube.com/watch?list=PL75DEC9EEB25A0DF0&feature=player_detailpage&v=uZ2SWWDt8Wg

This same youtube channel has dozens of similar combat videos. An autonomous killing drone system would save soldier's lives and kill fewer civilians. (drawbacks include high cost to develop and maintain)

Other, more advanced systems are also at least conceivable. Ground robots that could storm a building, killing anyone carrying a weapon or matching specific faces? The current method is to blow the entire building to pieces. Even if the robots made frequent errors, they might be more effective than bombing the building.

Building a whole brain emulation right now is completely impractical. In ten or twenty years, though... well, let's just say there are a lot of billionaires who want to live forever, and a lot of scientists who want to be able to play with large-scale models of the brain.

I'd also expect de novo AI to be capable of running quite a bit more efficiently than a brain emulation for a given amount of optimization power.. There's no way simulating cell chemistry is a particularly efficient way to spend computational resources to solve problems.