bisbee hotel

Chris

“While Chris‚Äôs view is unproven at the scale that Richard, Philip, & others are addressing it, the approach is – as Philip has commented in the past – quite large and contains a large potential solution space.”

This assertion is rather different from what I’ve argued. While *initially* it appears that the parameter space is quite wide, the constraints in terms of material parameters rapidly narrow that space. The statement from my first letter to Chris is as follows:

“‚ÄúSo, far from delivering the ability to synthesise ‚Äòmost arrangements of atoms that are consistent with physical law‚Äô or to manufacture ‚Äúalmost any‚Ķ product ‚Ķ.that is consistent with physical and chemical law‚Äù, an extremely judicious choice of materials system, possible intermediate/ transition states, diffusion barriers, and symmetry is required to attempt even the initial, most basic and faltering steps in molecular manufacturing. ‚Äú”

“Nanosystems and the concept of mechanochemistry have not been ‚Äòdisproven‚Äô, so far as I know.”-from preceding post.

Will a *small* subset of systems support a number of mechanosynthesis steps? I believe that with an appropriate choice of materials/ parameters (e.g. H:C(100) or H:Si(100)) that, yes, it will be possible to carry out a limited number of mechanosynthesis steps. The key issues are:

(i) Will universal assemblers (involving either an assembler unit that can pick up different tools *or* a family of assemblers where each unit carries out a different reaction) be able to handle all the elements in the periodic table (or all the reactive molecules synthesised by chemists, as Drexler suggests in “Engines of Creation”)? No – the viable parameter space is too narrow. (For example, we need to ensure a combination of close-to-zero dangling bond density, high diffusion barriers, and directional covalent bonds).

(ii) The surface physics and chemistry that dictate our ‘low level’ mechanosynthesis steps determine which types of surface property/geometry we will have at the higher levels of ‘abstraction’ (and, thus, a complete decoupling of levels of abstraction is simply not possible).

(iii) Error correction and reliability narrow down the viable parameter space still further. In addition, defect densities must be controlled and eliminated. (On this second point, note that there’s a free energy cost associated with a completely defect free surface (as compared to a surface with a non-zero density of defects) at any finite temperature. This is manifest, for example, in the expression for the Gibbs free energy).

…but I realise that I’m simply repeating myself at this stage and that this discussion could go round and round in circles ad nauseum. Until the feedback loop between experiment and theory is closed then we simply won’t make any progress. I therefore look forward to discussing the viability of proposed routes to mechanosynthesis with Rob Freitas.

Best wishes,

Philip

(iii)

Chris IMO is saying that some very useful work can and should be done assuming there’s underlying science available. Given the speed of regulation and human appreciation of new technologies, this strikes me as more true than not.

Philip, Richard and others (still IMO) are saying there needs to be work done on those underpinnings, narrowing them down to ‘real’ reactions that can be demonstrated and reproduced in labs. This is also extremely useful, as it WILL need to be addressed, prior to many of the problems and promises that the broad view offers.

While Chris’s view is unproven at the scale that Richard, Philip, & others are addressing it, the approach is – as Philip has commented in the past – quite large and contains a large potential solution space. Is it guaranteed that some of the specifics Chris is postulating will come 100% true? Nope. Is it reasonable to assume that SOME percentage of these capabilities might come to be? Well, that’s a personal judgement, isn’t it?

Nanosystems and the concept of mechanochemistry have not been ‘disproven’, so far as I know. There are many problems to address at the mechanochemical – or whatever alternate atomicly precise method! – level, without a doubt. But are there any solid limitations that prevent the possibility of new tools, new designs from solving these problems?

That’s a serious question, by the way – Obviously there are problems with many of the suggested implementations thus far (all the ones that I’m aware of, having had serious scrutiny). But do these problems indicate a flat out failure, or is there a missing breakthrough or breakthroughs? How much new science or engineering needs be developed before such capabilities as Chris proposes becomes possible?

-John

As for whether we think these difficulties are a show-stopper or not, I don’t actually think I said that. I rather suspect I might be more optimistic than you about the degree to which it will be possible to learn to live with and exploit the complexity of these systems. I think its going to be worth following the progress of systems biology very carefully over the next few years, and watching for the ways in which insights from chemical and cell computing get applied back into computer science.

in this scenario top down approach must be substituted by bottom up, where abstractions are chosen based on experiment, and not design.

anyway just an unqualified opinion, im no expert in nanotech.

Chris

Thanks for that post, David. This is certainly my (and Richard’s) assertion.

Best wishes,

Philip