Fabrication and friends

Recently, a friend of mine and I had a debate about universal fabrication in general and fabbers in particular. The conversation and resolution we came to were, I thought, worth writing about. Full disclosure: I’m a biologist and JP (my friend) is an engineer. Oh, and we both want to buy a fabber someday.

The conversation (heavily edited for reasons of dramatic flow and memory) went something like this:

JP: Universal fabrication as usually stated (one box that can make and assemble a copy of itself) is bogus. This is because the manufacturing process itself degrades information: Even a fabber that can produce a part with 0.01% loss will only ever produce something worse than itself. In effect, fabbing as usually stated boils down to photocopying a photocopy. Soon, the original image itself will be worthless.

Me: Okay, so what about using a secondary process to up efficiency again? Like, say, having the fabber first build a milling machine. The milling machine then works the part that was fabbed to produce a more accurate piece. The lost information is restored via a secondary process.

JP: Sure, but that only spreads the loss around. The milling machine will still be of a lower tolerance, so it can only ever mill to that standard.

Me: So how about approaching it from the other end? Simply make a population of parts and discard the ones that don’t fit. By this method, the accuracy of each new generation should actually go up a little until the physical limits of the design and materials used are reached. By treating the manufacturing process as a biological process instead of an industrial one, no information gets lost. Its industrial evolution!

JP: This wouldn’t work, for two good reasons. Firstly, its insanely wasteful to discard 90% of each production run in the name of quality control. The entire point of manufacture is to limit waste, so you might as well stick to current methods if the replacement sucks so much. Secondly, the machine would then have to choose which parts are good or bad. And the only way to do that is to compare them to a standard. And, given an internally-set standard (because the box must reproduce unaided), the standard itself will become a victim of information decay. A better way (and one which the industrial world is currently adopting) is to peg the standard to a physical constant (eg: a standard length measured using a specific wavelength of light). Unfortunately, by the time you’ve integrated the standard system and complex comparison system, you’ve essentially made a god-box: a manufacturing centre with the entire world standardisation system onboard, mated to a strong AI. So its doable, but not for another hundred years or so.

Me: But by simply discarding standardisation and quality control, you could do it with near-future technology. Once again, you use the biological approach: You have your mother fabber make and assemble lots of babies and only those that work will live to assemble the next generation. Basically, drop the whole ‘make me stuff’ function in favour of all-out replication and natural selection will take care of the rest.

JP: Which is great, except now you don’t have a fabber. You have a self-replicating machine that might, if you’re very lucky, do something useful on the side.

Me: Which is kind of what I deal with every day anyway. That’s biology. It sounds fine here.

JP: But its also useless if what you want is, say, for it to fabricate anything. A better approach would be to make fabbers using stock-standard industrial methodology (IOW: in a factory somewhere) and only have them produce the things you want them to. This would make them into another bench tool, like a lathe or milling machine, but bypass all of the issues around universal fabrication in one go.

Me: Fabbers still rock, though.

So, to recap: As a way to make complex shapes, fabrication is awesome. As a game-changing technology that will result in a revolution in how industry itself works, not so much. And as a way to produce A-life, hmmm…


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