I don’t think articles like this belong on Less Wrong, so I downvoted it.  Presumably the author agrees, to some extent, or he wouldn’t have felt the need to pre-apologize.   If people disagree with me, they are of course free to upvote it.

Also, the article in question was posted in October of 2020.  Why bring it up now?  It’s not like we can do anything about it.

“Time-Symmetric” and “reversible” mean the same thing to me: if you look at the system with reversed time, it obeys the same law.  But apparently they don’t mean the same to OP, and I notice I am confused.  In any event, as Mr Drori points out, symmetry/reversibility implies symmetry under time translation.  If, further, the system can be described by a Hamiltonian (like all physical systems) then Noether’s Theorem applies, and energy is conserved.

Now I know more!  Thanks.  

That would suggest that an equal mass of tiny wind turbines would be more efficient.  But I see really big turbines all over the midwest.  What's the explanation?

Yes.  I know him.  We met years ago when I was a grad student at the Media Lab.  I haven't followed his work on self-reproduction in detail, but from what I've seen he is not aiming at economically self-sufficient devices, while I am.  So I'm not too impressed.

As I describe in my first reply to Jackson Wagner above, I can tolerate some inefficiency, as long as I stay above Soviet-style negative productivity.  The goal is minimum reproduction time.  Once I've scaled up, I can build a rolling mill if needed.

You could mill every single plate in a motor core out of sheet stock on a milling machine...

As you point out, that would be madness.  I've got a sheet rolling machine listed, so I assume I can take plate and cold-roll it into sheet.  Or heat the plate and hot-roll it if need be. The sheets are only a meter long and a few centimeters wide, so the rolling machine fits inside.  They function like shingles for building the outside enclosure, and for various machine guards internally, so they don't have to be big.

where are you quenching the stuff?

I'm quenching in a jar of used lubricant.  Or fresh oil, if need be.  6% of the input is oil.

alloys isn't necessarily that you can't substitute X for Y, but that X costs three or four or ten times as much as Y for the specific application that Y is optimized for. 

I'm a little reluctant to introduce this kind of evidence, but I've seen lots of machinist videos where they say "I pulled this out of the scrap bin, not sure what it is, but lets use it for this mandrel" (or whatever).  And then it works fine.  I am happy to believe that different alloys differ by tens of percent in their characteristics, and that getting the right alloy is an important occupation for real engineers.  I just don't think that many thousands of them all vary by "three or four or ten times."  I think I can get away with six or so.

I was actually thinking of a pair of humanlike arms with many degrees of freedom, and one or more cameras looking at things.  You can have dozens of single datum sensors, or one camera.  It's much cheaper.  Similarly, once you have some robot arms, there's no gain in including many single use motors.  For example, when I include an arbor press, I don't mean a motorized press.  I mean a big lever that you grab with the robot arm and pull down, to press in a shaft or shape a screw head.

There are two CNC machine tools, to automate some part shaping while the robot does something else.  

Yes, absolutely!  A fine description of the current state of the art.  I upvoted your post by 6 points (didn't know I could do that!).  

 I'm imagining doing everything the machinist has to do with a mobile pair of robot arms. I can imagine a robot doing everything you listed in your first list of problems.  Your "stupider stuff" is all software problems, so will be fixed once, centrally, and for good on the Autofac.  The developers can debug their software as it fails, which is not a luxury machinists enjoy.

Call a problem that requires human input a "tough" problem.   We can feed the solutions to any tough problems back into the model, using fine-tuning or putting it in the prompt.  So ideally, any tough problem will have to be solved once.  Or a small number of times, if the VLM is bad at generalizing.  The longer we run the Autofacs, the more tough problems we hit, resolve, and never see again. With an exponentially increasing number of Autofacs, we might have to solve an exponentially increasing number of tough problems.  This is infeasible and will destroy the scheme.  We have to hope that the tough problems per hour per Autofac drops faster than the number of Autofacs increases.  It's a hope and only a hope-- I can't prove it's the case.

What's your feeling about the distribution of tough problems?  

Wow, I think that comment is as long as my original essay.  Lots of good points.  Let me take them one by one.

I see a few potential benefits to efficiency-imparing simplifications:

1. lt reduces the size/cost/complexity of the initial self-replicating system.  (I think this motivation is misplaced, and we should be shooting for a much larger initial size than 1 meter cubed.)

The real motivation for the efficiency-impairing simplifications is none of size, cost or complexity.  It is to reduce replication time.  We need an Autofac efficient enough that what it produces is higher value than what it consumes.  We don't want to reproduce Soviet industry, much of which processed expensive resources into lousy products worth less than the inputs.  Having achieved this minimum, however, the goal is to allow the shortest possible time of replication.  This allows for the most rapid production of the millions of tons of machinery needed to produce massive effects.

Consider that the Autofac, 50 kg in a 1 m^3, is modeled on a regular machine shop, with the machinist replaced by a robot.  The machine shop is 6250 kg in 125 m^3.  I just scale it down by a factor of 5, and thereby reduce the duplication time by a factor of 5.  So it duplicates in 5 weeks instead of 25 weeks.  Suppose we start the Autofac versus the robot machine shop at the same time.  After a year, there are 1000 Autofacs versus 4 machine shops; or in terms of mass, 50,000 kg of Autofac and 25,000 kg of machine shop.  After two years, 50,000,000 kg of Autofac versus 100,000 kg of machine shop.  After 3 years, it's even more extreme.  At any time, we can turn the Autofacs from making themselves to making what we need, or to making the tools to make what we need.  The Autofac wins by orders of magnitude even if it's teeny and inefficient, because of sheer speed.

That's why I picked a one meter cube.  I would have picked a smaller cube, that reproduced faster, but that would scale various production processes beyond reasonable limits.  I didn't want to venture beyond ordinary machining into weird techniques only watchmakers use.

I see a few potential benefits to efficiency-imparing simplifications:

1. ...
2. It reduces the engineering effort needed to design the initial self-replicating system.

This is certainly a consideration.  Given the phenomenal reproductive capacity of the Autofac, there's an enormous return to finishing design as quickly as possible and getting something out there.

To me, it seems that the Autofac dream comes from a particular context -- mid-20th-century visions of space exploration -- that have unduly influenced Feynman's current concept.

Let me tell you some personal history.  I happened upon the concept of self-reproducing machines as a child or teenager, in an old Scientific American from the fifties.  This was in the 1970s.  That article suggested building a self-reproducing factory boat, that would extract resources from the sea, and soon fill up the oceans and pile up on beaches.  It wasn't a very serious article.  Then I went to MIT, in 1979.  Self-reproducing machines were in the air-- Eric Drexler was theorizing about mechanical bacteria, and NASA was paying people to think about what eventually became the 1981 lunar factory design study.  I thought that sending a self-reproducing factory to the asteroid belt was the obvious right thing, and thought about it, in my baby-engineer fantasy way.  But I could tell I was ahead of my time, so I turned my attention to supercomputers and robots and AI and other stuff for a few decades.

A few years ago I picked up the idea of self-reproducing boats again.  I imagined a windmill on deck for power, and condensing Seacrete and magnesium from the water for materials.  There was a machine shop below decks, building all the parts.  But I couldn't make the energy economy work out, even given the endless gales of the Southern Ocean.  So I asked myself, what about just the machine shop part?  Then I realized the reproduction time was the overriding consideration.  How can I figure out the reproduction time?  Well, I could estimate the time to do it with a regular human machine shop, and I remembered Eric Drexler's scaling laws.  And wow, five weeks?!  That's short enough to be a really big deal!  So, a certain amount of calculation and spreadsheets later, here we are, the Autofac.

I considered varied environments for situating  the Autofac:

• a laboratory in Boston.  Good for development, but doesn't allow rapid growth.
• a field near a railroad and power line in the Midwest.  Good for the resource inputs, but the neighbors might reasonably complain when the steel mill starts belching flame, or the Autofacs pile up sky-high.
• Baffin Island.  Advantages described above.
• Antarctic Icecap.  Bigger than Baffin, but useful activities are illegal.  Shortage of all elements except carbon, oxygen, nitrogen and hydrogen.
• The Moon.  Even bigger.  Ironically, shortage of carbon, nitrogen and hydrogen.  No wind, so the Autofac has to include solar cell manufacture from the git-go. There will be lots of problems understanding vacuum manufacturing.  Obvious first step toward Dyson Sphere.
• Carbonaceous asteroids.  Obvious second step toward Dyson Sphere.

So, I decided to propose an intermediate environment.  Obviously, it was rooted in the mid-20th-century visions of space exploration.  But that didn't set the size, or the use of Baffin Island, or anything else really.  We'll build a Dyson Sphere eventually, but I don't feel the need to do it personally.

More to come.

If you look at what I wrote, you will see that I covered both of these.

Yeah, I looked at various forms of printing from powder as a productive system.  The problem is that the powder is very expensive, more expensive than most of the parts that can be produced from it.  And it can’t produce some parts— like ball bearings or cast iron— so you need tools to make those.  And by the time you add those in, it turns out you don’t need powder metallurgy.