[ExI] von Neuman machines

Adrian Tymes atymes at gmail.com
Sat Aug 27 05:24:00 UTC 2016

On Fri, Aug 26, 2016 at 6:28 AM, Keith Henson <hkeithhenson at gmail.com>

> The trouble is, if you talk about a 20 year replication time, a lot of
> the problems may go away, but so does the motivation.

Yes, but this is true of many existing implementations of nanotech too.
Let's say you start with something atom-sized that can replicate something
atom-sized.  You build up until you have enough for each atom in a human
body, then do one more step to replicate said human body.  According to one
site in a quick search, there are roughly 7 * 10^27 atoms in an average
human body.  10^3 is roughly 10 doublings, so this is 93 doublings to get
to the right number + 1 to replicate the human.  If each doubling takes a
week, that's just shy of 2 years...and that's just for something about the
size of a human.

The trick is to find a machine shop setup that can replicate itself fast.
Optimized nanotech allows for precision, but not necessarily speed.

> > Once you have that set, what can make more of themselves and said
> > manipulators?
> >
> > ...and the control circuitry and power systems?
> >
> > ...and machinery to gather and smelt regolith?
> Regolith is not like iron ore.  Even if it was, you don't have the
> carbon and free oxygen to power the smelting.

Yes, granted, this is in the context of being on the Moon and using
regolith.  This is a design challenge, but not an impossibility.

But e.g. you're not making carbonized steel for structural elements.  You'd
more likely use aluminum for that.

Nor can you scale down
> processes that involve a lot of heat.

You can, but it's tricky and less efficient.  (CubeCab is doing this a lot,
in a sense.)

> > Rather than focusing on one tool to do it all, think of it as an
> industrial,
> > mostly automated city expanding from a seed.  There will be many things
> it
> > can not fabricate, at least at first.  But if you have a
> limited-capability
> > factory build another such factory, then you have two factories, and I'm
> > sure you're familiar with the math from there.
> The critical parameter is replication time.  A lot of the steps like
> chemical sorting out elements are just slow.

Rely more on heat, cyclotrons, and diffusion, and less on chemicals.
Besides, chemical processes often turn out to rely on reagents you wouldn't
have up there.

> Not trying to be a wet blanket on the subject, but it is way harder
> than it looks.

Oh, quite agreed.  If it were easy it'd have been solved by now.  You have
to discard a lot of processes that would be the obvious way to do it on
Earth, and rely on or come up with ones that would work on the Moon.  And
then you have to come up with a means of fairly rapid replication.  Nothing
suggests that it is physically impossible; it's just that we don't know how
to do it all yet.

I anticipate a growing number of lunar experiments over time to try to
solve subsets of this problem (as lunar access for small-budget experiments
becomes more and more practical over the next several years), prior to a
full-up bootstrapped lunar factory becoming viable.  And you do (or, at
least, someone does) have to break the problem down into subproblems in
order to solve the whole thing, at least from where we are now.
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