[extropy-chat] Re: Nano-assembler feasibility

[Eugen Leitl]

On Sun, Mar 28, 2004 at 09:13:58AM -0800, Hal Finney wrote:

> I agree with much of Brett's skepticism on this issue.  Given the fact
> that so many prominent scientists continue to maintain that assemblers
> are impossible, supporters of the concept need to take on the burden
> of proof.  It's not enough any more to say, tell us why it won't work.

If this was just an intellectual debate, with nothing else but participant's
egos or maybe their tenure at stake, that's a perfectly rational view to take.

However, successful molecular manufacturing is a very disruptive technology both in
terms of payoff and risk. As such we as a society simply cannot take any
risks to not try to investigate the issues practically.
 
> In the case of assemblers, we're missing the most important pieces:
> the parts which do assembly.  We can invent bearings and struts,

Absolutely. We're missing a library of deposition steps modelled in machina
and validated experimentally. However, we have both increasing evidence that
mechanosynthesis is both easy and rich, and that current nanolithoprinting
processes scale into the nano range.

> cables and even works of art like the fine motion controller.  But I

These are just mock-ups, instances of structural spaces very distinct from
biology. They are very much not authoritative blueprints. There's no point in
give them that degree of scrutity as if they were.

> have yet to see any proposal for how these pieces can be built.  I mean
> specifically what tool-tips will be used, how they will be swapped out,

There is a continuum of approaches to self-rep molecular systems. We know
self-assembly works, and has very large processivity due to intrinsic
parallelism. This would work on all scales, beginning from folded linear
biopolymers, engineered biopolymers, biopolymer analoga and completely
synthetic analoga, as well as small cycles and cages, large complementary
surfaces, and even macroscale assembly. It's a sufficiently powerful paradigm
to reach full-closure self-replicating and autopoietic systems. Machine-phase
goes a long way to more control, but it clearly pays the price in energy and
processivity. I personally think swapping discrete too tips is a red herring.
It's unnecessary, and it results in massive increase in complexity and
decrese in processivity. Continous processes are better than discrete cycles.
Hollow ducts and small-molecule and linear-strand monomers are good enough to
do 3d nanolithoprinting of structural parts. Self-assembly is good enough for
3d crystalline computation. A bucky mill processing batches of stochastically
synthesized substrate, sorting and covalently modifying, and assembling
structures looks far better to me than building stuff by hammering reactive
moieties down on HOPG or diamond in UHV.

Latter's probably very feasible, just difficult to get to and not the optimal
way of doing things every time.

So we have a large space of approach candidates. Instead of sterile
arguments about feasibility of XY, we should explore as many of these
pathways as possible, pumping as much R&D resources as we can syphon away
from other areas of human enterprise. 

> and what construction sequences will be used to build the components.
> 
> Now, there are two parts to this question.  The first is, how can an
> assembler self-replicate; how can it build its own parts.  (Downplaying
> self-rep is not relevant here; obviously the system composed of the

Self-rep is closure over unity. I agree with you that self-rep is the key
component for truly successful nanotechnology -- but being assistive in its
own manufacturing goes a long way towards that. Current semiconductors make
good headway towards nanoscale (90 nm feature size right now), and they're
very useful in their own design and production cycle.

Semiconductor nanolitho won't give us chips for the same price as potato
chips, but alternatives might. 

> assembler plus supporting technology has to be able to replicate
> in some way, otherwise we'll only have one assembler.)  The second,
> even more difficult, is how can we bootstrap into an assembler from
> today's technology; how can we build its parts without already having
> an assembler.

...
 
> This is why the alternative strategy is being tried, of claims that we
> already have enough data to know that we will succeed.  But I think the
> political reality today is that this strategy is not working.  The only
 
If you mean, allocation funds for R&D, that's accurate. Maybe the opportunity
to reach Drexler/Merkle/Freitas device country by big federally funded science 
is blown for good, but maybe we don't need that route.

> alternative is to take many years of time and effort to tackle these
> problems one at a time, until we do get to the point where we have a
> design that answers all the questions and eliminates the objections,
> by construction.

I think the reality will gently assemble itself, coming from organic and
polymer electronics, with possible confluence of self-assembly molecular
memory and electronics and manipulative proximal probe. Probably it will be
by another route entirely. It's too early to tell.

As usually, reality tends to become normative in pretty unexpected ways. 

-- 
Eugen* Leitl <a href="http://leitl.org">leitl</a>
______________________________________________________________
ICBM: 48.07078, 11.61144            http://www.leitl.org
8B29F6BE: 099D 78BA 2FD3 B014 B08A  7779 75B0 2443 8B29 F6BE
http://moleculardevices.org         http://nanomachines.net
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 198 bytes
Desc: not available
URL: <http://lists.extropy.org/pipermail/extropy-chat/attachments/20040331/f5094906/attachment.bin>