Also, you don’t have to restrict yourself to adding atoms; there’s nothing wrong with taking them off. For example, you could passivate a surface, removing H atoms just where you want to deposit C, and then passivating what you just deposited and moving to the next site where you remove H, deposit C, hydrogenate…

But I don’t think “universal” is important. Certainly the word and the concept have not been a part of nanofactory proposals. A nanofactory can be very flexible, even general-purpose, with just a few reactions and atom types. You can do a lot without ever getting into atoms heavier than chlorine (except perhaps as catalysts for mechanosynthesis in a narrow set of special-purpose molecules). Build a “toolbox” of nanoscale components, and simulate anything else. The toolbox might not need much more than actuators, wires, digital logic, bearings, structures, mechanosynthetic tools, and maybe photon stuff.

Chris

First, I very much look forward to reading Drexler’s most recent work when it’s published. It’ll be interesting to see whether the error rate (in the calculations) is significantly lower than that in Freitas et al.’s work and, moreover, whether there is a useful strategy for “porting” the theoretical study to experiment.

I’m not certain that I agree with you on the “universal assemblers” point. You seemingly argue that Drexler suggests that we’d need a family of assemblers (one for each reaction). That’s not at all how I interpret the section in Engines of Creation which you cite. Drexler states that the assemblers “will be able to use as “tools” almost any of the reactive molecules used by chemists – but they will wield them with the precision of programmed machines”. This strongly suggests to me that an assembler will be able to pick up various tools to carry out different reactions. What you’re suggesting is much closer to the ‘molecular mill’ concept…

Nevertheless, even if a family of assemblers (one for each reaction) is to be used, the problem is that the parameter space is severely limited by the choice of material/ surface/ reactant. For example, high dangling bond densities are ‘verboten’ (so we need to use passivated surfaces), high diffusion barriers are required (ruling out a number of metal surfaces), directional covalent bonds are required..etc..etc.. Leaving aside our discussion of diamondoid mechanosynthesis for a while, the idea that one can construct a family of assemblers with each assembler dedicated to a particular reaction **for practically every element in the periodic table** is deeply flawed.

Philip

Chris

On material systems and reactions: Drexler has done some very interesting work over the last few months, that will be published over the next few months. Basically, he’s found a tool that does not leave dangling bonds on the tool when the deposited moiety is removed. Thus the transfer is far more energetically favorable than the Freitas/Merkle tool, and the dimer will reliably leave the tool when given a chance to move to diamond, graphite, or buckytube.

Chris

A point. However, diamond (and potentially other carbon materials – graphenes, buckytube, buckyball) does not do everything that you’d want objects to do. For instance, diamond is slightly unstable in ‘normal’ PVT conditions, buckytubes are vulnerable to atomic oxygen degredation, etc.

While diamondoid mechanochemistry, if it comes to be, would be wonderful in many ways, it won’t solve the ‘universal assembler’ problem. That is, there’ll still be lots of problems that need solutions using non-carbon materials.

However, it *may* be possible to use a carbon nanoassembler to make the tools to make the tools to do the job you want. IE – use diamondoid reaction vessels to handle chemical synthesis of other elements to make ‘food’ or other materials that aren’t just carbon. This is a non-trivial R&D project, however, on top of the already non-trivial R&D needed to get diamondoid mechanochemistry – or any other nanofactory/molecular mill capability – off the ground.

-John

-John

Chris Phoenix and I have covered very many issues related to your post in our recent debate. This will be published in its entirety on “Soft Machines” in the near future. I’d very much like to hear your comments on the debate and if your questions haven;t been addressed by the material in the debate, I’d be more than happy to go into more detail.

Best wishes,

Philip

Second off – Dr Moriarty – Your arguements above seem to indicate that you’re targetting the concept of ‘general’ or ‘universal’ assemblers as being beyond reasonable, and make some very good arguements along those lines. However, does this doom mechanosynthetic nanotech, in your opinion?

Would it be ‘enough’ to be able to create carbon-carbon bonds in 3D, creating fullerines, diamondoid, and/or graphite type products? Would this or would this not be a reasonable initial goal, gaining a large amount of nanotechnological wet-dream capability in this way for a relatively minute number of chemical interactions that would need to be supported?

If this is ‘good enough’, what is your position on Merkle’s paper on mechanochemistry or ‘hydrocarbon metabolism’ (at http://www.zyvex.com/nanotech/hydroCarbonMetabolism.html)? (My apologies if I’ve missed reference(s) to your position previously, but I’ve not run across them in the reading I’ve done…)

Sincerely,
John B