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A metallurgist's doubts about self-replicating probes

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Re: A metallurgist's doubts about self-replicating probes

#51

Post by M95D »

qnleigh wrote: post #48
marcosdumay wrote: post #27

Yes, we don't know how to make a half-ton replicating probe right now. No, none of the arguments on the article have any implication on the possibility of such a probe. None at all. There's something to look into at the durability argument. The article has no usable information on it, and it's probably not a showstopper. But again, the only thing on the article is that yes, we don't know how to make one such probe ri…

I would also think that self-replicating probes would work more like living things. He seems to be imagining that we make probes like modern machines, and then find ways to let them build themselves. But nature found much easier solutions.

Life as we know it until now has big difficulties outside goldilocks zone. It would theoretically be possible to make microbes (or fish?) that float high in Venus atmosphere, if we put money into 200 years of research, but no way life as we know it could ever break up and "eat" an asteroid.

Re: A metallurgist's doubts about self-replicating probes

#52

Post by scythe »

abecedarius wrote: post #21
seiferteric wrote: post #9

Wouldn't a counter this argument be biological systems? These are reasonable points as long as we are talking about current methods, but I assume if we were to get to the point of self replicating probes it would be done by something like nanotechnology, synthetic biology like systems.

Yes, I was wondering why the focus on metals. (Admittedly they might be needed in trace amounts for catalysis, or convenient for conductors, etc., or for structural material if you're on a carbon-poor asteroid. Most metals are worse than carbon for the latter if you have reasonably high tech.)

Carbon does not beat metal structurally. Some organic polymers are competitive in tensile strength. In flexural strength and fracture toughness, alloys continue to rule. And when carbon materials are competitive in strength and toughness, they tend to be highly temperature-sensitive and have sudden failure modes, which is not great for operating in space. Consider e.g. the Titan submarine that failed due to carbon fiber composite fatigue.

Re: A metallurgist's doubts about self-replicating probes

#53

Post by bunderbunder »

marcosdumay wrote: post #29
simiones wrote: post #28

Earlier quoted context omitted.

I hate this assumption that many sci-fi enthusiasts seem to make, that as long as something is not ruled out by currently known physics rules, it doesn't matter that we have no idea how it could be built, there will be some way in some plausible future. When we see currently insurmountable problems in creating a piece of technology, it's absolutely possible that we'll never be able to build it. Even if it is theoreti…

It's absolutely possible that we'll never be able to build it. There's absolutely no evidence of that on the article.

Of course not. That isn’t what the article was trying to say.

The thesis was, “I would like to suggest that the hardest part is the one that gets a single sentence: ‘mines local material and builds a copy.’” And so naturally the points in the article are only trying to support that point.

The closest we get to what this thread is talking about is the concluding remark on the Fermi paradox. Which doesn’t rest on the idea that it’s a practical impossibility; just on the suggestion that it may be hard enough that we can’t just assume civilizations that are in principle capable of building them are likely to actually do it.

Re: A metallurgist's doubts about self-replicating probes

#54

Post by M95D »

alwa wrote: post #37
pfortuny wrote: post #32

Earlier quoted context omitted.

The self-replication assumes also that there is enough energy stored in each planet (or coming from a Sun) to do the work... That is pretty much unlikely.

And stored in the specific forms the machine can exploit. Over a long enough timescale, though… really, really slow solar trickle charge to a space-capacitor bank? A thousand years’ suns, culminating in a glorious orgy of smelting?

Unless the capacitor breaks down before it's charged, one of the main problems discussed in the article.

Re: A metallurgist's doubts about self-replicating probes

#55

Post by abecedarius »

scythe wrote: post #52
abecedarius wrote: post #21

Earlier quoted context omitted.

Yes, I was wondering why the focus on metals. (Admittedly they might be needed in trace amounts for catalysis, or convenient for conductors, etc., or for structural material if you're on a carbon-poor asteroid. Most metals are worse than carbon for the latter if you have reasonably high tech.)

Carbon does not beat metal structurally. Some organic polymers are competitive in tensile strength. In flexural strength and fracture toughness, alloys continue to rule. And when carbon materials are competitive in strength and toughness, they tend to be highly temperature-sensitive and have sudden failure modes, which is not great for operating in space. Consider e.g. the Titan submarine that failed due to carbon fi…

All our structural carbon is low tech by the relevant standards (civilization that can send star-seeds). https://dspace.mit.edu/entities/publication/49f95196-2ddf-48...

Re: A metallurgist's doubts about self-replicating probes

#56

Post by bunderbunder »

Windchaser wrote: post #39
andrewflnr wrote: post #19

Earlier quoted context omitted.

Somewhat famously with life, you aren't necessarily replicating the same thing at the end as you are at the beginning, which is an awkward property for an engineered system.

So that adds some extra "benefits" (mutation and natural selection improves the probes over time) along with some extra difficulties - how do you keep the self-reproducing probes "on-task" from one generation to the next? How do you instill "explore and report home" as an innate goal to a mutating system?

I would argue that, over the time scales at which Von Neumann probes would hypothetically spread, “report home” may be a useless or even wasteful requirement. Even if somebody were still around to hear the message, what is the likelihood that they would still be listening? Or be able to interpret it?

Re: A metallurgist's doubts about self-replicating probes

#57

Post by abecedarius »

EA-3167 wrote: post #35
abecedarius wrote: post #30

Earlier quoted context omitted.

> complex and interdependent ecosystem That's why my other comment pointed to the autotrophs with the simplest requirements, and the (unknown but complexity-bounded) origin of life. > pace of biological activity is a lot slower than industrial ones Bacterial replication times can be under an hour.

You’re absolutely right about how quickly some bacteria can replicate, but that depends on the proper substrate, ambient conditions, availability of nutrients, and any competition from contaminants. What something like E. Coli can do in a well bioreactor is the ideal case, and even then most of what they produce is the bacteria themselves. On Earth this isn’t a problem at all, but as a means of husbanding every joule…

Mainly my point there is that it doesn't seem reasonable to anchor advanced nanotechnology on the doubling times we're used to for industry. I don't want to guess just what to expect for early construction from a starseed arriving at e.g. an outer-solar-system carbon-rich moon -- but nothing like a human generation.

Re: A metallurgist's doubts about self-replicating probes

#58

Post by torginus »

simiones wrote: post #23
abecedarius wrote: post #21

Earlier quoted context omitted.

Yes, I was wondering why the focus on metals. (Admittedly they might be needed in trace amounts for catalysis, or convenient for conductors, etc., or for structural material if you're on a carbon-poor asteroid. Most metals are worse than carbon for the latter if you have reasonably high tech.)

The thing is, while the universe is full of metals, it's not that full of the materials needed to sustain life (as we know it, at least). You can find metals and other inorganic compounds on virtually every asteroid, moon, and planet, and many comets even. But water and nitrogen and carbon are significantly rarer. Plus, life can't survive more than a few minutes in space without metal encasings and electronic life su…

Actually the other way around:

https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elem...

There's tons of Carbon, Nitrogen and Oxygen in the universe, but very little metals. Heavier elements are much rarer.

Re: A metallurgist's doubts about self-replicating probes

#59

Post by ordu »

marcosdumay wrote: post #29
simiones wrote: post #28

Earlier quoted context omitted.

I hate this assumption that many sci-fi enthusiasts seem to make, that as long as something is not ruled out by currently known physics rules, it doesn't matter that we have no idea how it could be built, there will be some way in some plausible future. When we see currently insurmountable problems in creating a piece of technology, it's absolutely possible that we'll never be able to build it. Even if it is theoreti…

It's absolutely possible that we'll never be able to build it. There's absolutely no evidence of that on the article.

> There's absolutely no evidence of that on the article.

If you treat evidence as in the law of excluded middle, then yes. But if you are ready for a probabilistic evidence, then the article is a piece of evidence.

It chains Fermi Paradox, and our lack of knowledge how to do metallurgy in space. They both combined raise probability of impossibility of Von Neumann probes. It is not a proof that rules out Von Neumann probes, but it raises doubts about them.

Re: A metallurgist's doubts about self-replicating probes

#60

Post by torginus »

scythe wrote: post #50
seiferteric wrote: post #9

Wouldn't a counter this argument be biological systems? These are reasonable points as long as we are talking about current methods, but I assume if we were to get to the point of self replicating probes it would be done by something like nanotechnology, synthetic biology like systems.

Biology ignored some of the most abundant elements because they can't be worked with under the constrained temperature and pressure conditions where biological systems operate. Biology barely uses any silicon, even though it is the second-most common element in the biosphere. Biology does not use aluminum, the third-most common element, at all. Biology does use iron but cannot reduce it to the pure metal. In fact, bi…

The most abundant elements are the ones biology works with (except for Helium ).
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