[seiferteric]

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.

[Diogenesian]

Why would biological systems be a counterargument? Smelting metals and sustaining life both require an enormous amount of water and about ~1ATM of atmosphere, as far as we know, and there's no plausible known mechanism for sidestepping this requirement. So "magical synthetic biology that can self-replicate in space" is actually a worse solution to the problem than "magical metallurgy that can be done in space" since humans at least have smelted metals, but we've never built synthetic forms of life. (Not counting CRISPR)

[AlotOfReading]

You're making assumptions that the parent isn't necessarily making. Imagine sending humans to other earthlike planets on hypothetical generation ships. Those humans could throw away their technology and rebuild from zero over thousands of years to send more spaceships of humans to yet further planets. Presto, an example of self-replicating biological von Neumann systems.

[EA-3167]

It's important to say that isn't self-replicating in the von Neumann sense, even setting aside the question of how it's being executed. Humans don't replicate, we reproduce and critically evolve, never more quickly or drastically then when we're introduced to a new environment with new selection pressures. Unless these future humans have the technology to avoid that natural drift then they won't be a probe for the original species in any sense, they will speciate. In fact if you send people on a one-way trip to start over from scratch, I think it's pretty extreme to imagine their nth descendants caring about the goals of the parent civilization. Even if they in turn become spacefaring it's not as though they'll act as "probes" for their ancient and probably forgotten ancestors.

[AlotOfReading]

There are decades old papers [0] on this subject that explicitly use humans as a analogy and call it "reproduction" because of the need to learn or evolve for local conditions. I don't think using terms in a way they've been used since the first serious analysis of the concept is going to confuse anyone.

    I think it's pretty extreme to imagine their nth descendants caring about the goals of the parent civilization.

It's an example to demonstrate the concept in familiar terms, not a psychohistorical prediction.

[0] https://www.rfreitas.com/Astro/ReproJBISJuly1980.htm

[andrewflnr]

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.

[Windchaser]

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?

[EvanAnderson]

I'd argue all self-replicating systems subject to entropy (i.e. existing in the physical world) are automatically subject to mutation and natural selection and, therefore, alive and able to evolve around any innate goals or constraints. If the inmate goal isn't tied to a highly-conserved phenotype I would think the goal would disappear as mutations accumulate and natural selection takes its toll.

[fragmede]

Judging by our behavior on the current rock we're on, don't give them the choice. Humanity has been around for a long time. In that time, I don't believe I've ever heard discussion of changing the direction the Sun and Earth are headed. If there were something deep inside the Earth, or another planet that would activate in another 10,000 years that would do the phone home step, we still don't know about it. So while we're hypothesizing about sci-fi Von Neumann probes, just scale the entire thing up to the size of a solar system and send that off in the right direction. Collect all the mass in our system that isn't Sol, Terra, (and Luna), and build a rogue planet with an underground civilization, and then don't give them engines. Unless the civilization on the planet advances too the point that they can create engines, decide they don't want to go where you've sent them, voila, generational ship. Just bury a computer deep I side the rogue planet's core that activates once it reaches the destination.

[bunderbunder]

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?

[EvanAnderson]

If we build self-replicating machines and send them out into the universe we're really just sending out our evolutionary progeny. Hopefully they would remember us fondly.

[andrewflnr]

> how do you keep the self-reproducing probes "on-task" from one generation to the next?

This is, indeed, the exact question one must ask before attempting to build and launch biological Von Neumann probes.

[Windchaser]

I think it applies to non-biological Von Neumann probes as well. It'll apply to any system that can mutate, even if that mutation is just cosmic rays flipping the bits on a hard drive.

[scythe]

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, biological systems produce no metals. Structurally, biology relies on weak minerals like calcium carbonate and calcium phosphate, rather than much stronger ones like quartz and alumina, because of the difficulty of biochemical processing.

This isn't insurmountable for a probe. Biology can get stuck in local optima. Humans have the Periodic Table and quantum mechanics. But it means we are on untrodden ground. Refining titanium, today, uses a massive molybdenum-lined reactor operating at 1600 C (2900 F). The alternative processes (FFC and Chinuka) use liquid calcium chloride, mp 773 C. The square-cube law points to enormous energy losses trying to scale these processes down. And that's just one element.

[pavel_lishin]

> In fact, biological systems produce no metals

I'm going to be very pedantic and point out a counterexample: https://en.wikipedia.org/wiki/Scaly-foot_gastropod

[scythe]

Is greigite a metal? It is definitely a more interesting mineral, I'll give you that.

[torginus]

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

[scythe]

Iodine? Molybdenum? Cobalt?

[torginus]

Not by a long shot.

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

[palmotea]

> 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.

Biological systems require extremely specific environments that aren't space.

Yeah, you can self-replicate (well, not exactly self-replicate), but just think of all the "infrastructure" you need to do that: massive volumes of air and water, all kinds of weird chemicals not found in minerals, a whole biosphere of other stuff, a literal star, etc. And none of that infrastructure is really space-worthy on any reasonable scale for a probe.

If you broke it all down, I bet you'd need a mass/volume at least as big as a more technological probe. And you still need the technological infrastructure to build a vessel to hold it all together.

[abecedarius]

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.)

[simiones]

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 support; whereas metal alone only requires life at a much longer time scale. So, while it may be possible to build a fully inorganic self-replicating fleet, it's certainly impossible to build a fully-organic one with any technology or chemistry we know about today at least.

[abecedarius]

In the outer solar system organics and water are abundant (and in the inner there are plenty of carbonaceous chondrites, admittedly not the most generic inner-system bodies).

Agreed that metals should unlock wider opportunities in the inner system where solar energy is more abundant. I just don't think it matters much, you need a good place to plant your seed; once you've built up to scale you can then build wherever.

(False that life dies in minutes in space; plus the engineers can invest in even greater error correction than radiodurans.)

[simiones]

> (False that life dies in minutes in space; plus the engineers can invest in even greater error correction than radiodurans.)

What form of life can actually survive (that is, continue living, not just go into some dormant state from which it can later resurrect like a tardigrade) in space for more than a few minutes?

[torginus]

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.

[simiones]

Not in rocky bodies, except maybe for Oxygen (which is commonly found in the form of oxides, very rarely as a gas). Carbon and Nitrogen and Hydrogen and similar elements are mostly found in gas clouds and star that are not really conducive to any form of life or even really fit for extraction by a probe. Maybe some gas giants could be targets for a process of this kind?

[EA-3167]

Life as we know it relies on a complex and interdependent ecosystem, and complex life relies on countless other organisms to support us. Without plants we absolutely couldn’t survive, without microorganisms we can’t survive. Without ample supplies of food, water and oxygen we can’t function.

Generally speaking the pace of biological activity is a lot slower than industrial ones too. We might make up for the pace with scale, but then you’re back to the hard problem of dependencies and “fuel”.

I’m not sure that the problem of beneficiation changes because the system is biological rather than industrial. Edit: Without carrying whole ecosystems with the probe at least.

[abecedarius]

> 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.

[EA-3167]

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 because you don’t know when or where the next one is coming from, I think it might matter.

It’s also probably a genuinely hard problem keeping your organisms viable without a constant supply of food, a means to get rid of mutants, or some hitherto unknown means of preservation that could handle the extreme time spans involved between “awakenings”.

[abecedarius]

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.

[scythe]

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.

[abecedarius]

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...

[artemonster]

We are selfreplicating bots - can eat anything, self healing minor damage, very agile, autonomous. When we stop growing numbers the harvest will begin

[pjio]

> When we stop growing numbers the harvest will begin

I like this part. It gives me chills.

[seiferteric]

thats what i meant.

[golem14]

... but traveling for months, years, decades and millennia in space away from earth has proven difficult so far. Even astronauts in space for a year had significant changes afterwards.