Von Nuemann Machines

[SomeGuy123]

2 minutes ago, Jouni said:

The matter used in construction is not "outside help". In order for the machine to replicate itself reliably, it must already know which materials it needs and how they're going to be used. Therefore the machine must already contain all relevant information about the materials. Any remaining information content is just random noise that can only make the replication less reliable.

No.  That's not true.  A living cell doesn't know the atomic properties of carbon.  It just happens to have traps that bind to carbon.  DNA doesn't have the information describing the materials the cell is made from.  

Anyways, a functional copy of the earth is not what you're making it out to be.  Suppose there were in fact 10 other dead rocks, exactly earth sized and the same distance from the sun and the same element composition but missing the biosphere.  Somewhere in our galaxy this is true.

So you transplant enough pieces of the biosphere to terraform the planet.  You move over enough colonists and enough machinery to make a new civilization.  You wait a few thousand years.  There you go, a functional copy of the Earth.  The colonization of the Americas is just a microcosm, simplified copy of this.  Sure, starting with a planet without atmosphere or bacteria or trees or anything else is a lot harder but it's possible if the elements are there.

A von neumann machine is just a vastly more efficient way to do this.  Nobody ever said it had to be an exact copy, just a functional one.  And evolution means as you make copies after copies of these machines, the ones that turn out badly due to random chance and can't copy themselves either "die" or stop contributing to new generations.  So the overall pool of them continues to exist.

Frankly, I am really unsure what you're saying.  You're pulling out theories of math that depend on a very rigid set of assumptions and the evidence is overwhelmingly clear something doesn't apply.  I don't know these theories, nor do I have any particular interest in them - we really could get started on doing everything I described without ever working out why this is possible.  We just know it is because we have similar systems that do work so a theory that says they don't work is incorrect.

[Jouni]

8 minutes ago, SomeGuy123 said:

No.  That's not true.  A living cell doesn't know the atomic properties of carbon.  It just happens to have traps that bind to carbon.  DNA doesn't have the information describing the materials the cell is made from.

A living cell doesn't self-replicate in the sense a Von Neumann machine would. It lives in an ecosystem much more complex than the cell itself, and receives highly refined materials from the ecosystem. Remove the ecosystem and the materials, and the cell can't replicate anymore.

When we're talking about Von Neumann machines, we're talking about systems with no known precedent in the universe.

8 minutes ago, SomeGuy123 said:

So you transplant enough pieces of the biosphere to terraform the planet.  You move over enough colonists and enough machinery to make a new civilization.  You wait a few thousand years.  There you go, a functional copy of the Earth.  The colonization of the Americas is just a microcosm, simplified copy of this.  Sure, starting with a planet without atmosphere or bacteria or trees or anything else is a lot harder but it's possible if the elements are there.

This was also discussed in the earlier thread. My point seems to imply that building truly self-sustaining colonies is impossible, unless the colonized system already has a sufficiently complex ecosystem.

8 minutes ago, SomeGuy123 said:

Frankly, I am really unsure what you're saying.  You're pulling out theories of math that depend on a very rigid set of assumptions and the evidence is overwhelmingly clear something doesn't apply.  I don't know these theories, nor do I have any particular interest in them - we really could get started on doing everything I described without ever working out why this is possible.  We just know it is because we have similar systems that do work so a theory that says they don't work is incorrect.

My main assumption is that physics can be described, simulated, and understood. If that's true, the universe is equivalent to a Turing machine, and many things turn out to be logically / information-theoretically / statistically impossible and/or computationally infeasible. If your claims are incompatible with these theories, the claims are wrong, you're abandoning basic logic, or you're saying that the laws of physics can't be described. You can't ignore the fundamental laws of logic and nature just because you don't know them.

The claim that self-replication is impossible is based on some further assumptions and unproven ideas. I think it's true, because it feels intuitively obvious, once you're familiar with the impossibility results. Proving the claim or even developing the concepts necessary to discuss it in sufficient detail would require major scientific breakthroughs.

[peadar1987]

I think "grey goo" is pretty unlikely. In order for that to work, you would need titanic amounts of energy, and unimaginably complex machines. Do they run on solar power? What are the solar panels made of? Is there enough silicon in the immediate vicinity to make them? What about the impurities needed for doping? Send some nanobots out to find some? Let's hope they can be found within a few centimetres of your fabrication plant, because otherwise they'll be months getting back. What if they land in the sea? The desert? On top of a mountain? Vastly different conditions, and the only common way of utilising energy and self-replicating in all those places that we know of is by photosynthesis (or by consuming things that photosynthesise). You can maybe, maybe, make graphene out of carbon dioxide in the air, but even that's banking on it being there in the first place, and isn't applicable to every body you're going to end up on.

So your nanobots aren't going to be much "better" at consuming entire planets than photoplankton. They're subject to pretty much the same limitations, except perhaps less predation.

[PB666]

On December 9, 2015 at 7:20:04 AM, Plusck said:

Absolutely. Releasing such a probe is probably the single greatest crime a space-faring civilisation could commit.

I thought that was reserved for making an alliance with the grox.  ;^)

[PB666]

4 minutes ago, peadar1987 said:

I think "grey goo" is pretty unlikely. In order for that to work, you would need titanic amounts of energy, and unimaginably complex machines. Do they run on solar power? What are the solar panels made of? Is there enough silicon in the immediate vicinity to make them? What about the impurities needed for doping? Send some nanobots out to find some? Let's hope they can be found within a few centimetres of your fabrication plant, because otherwise they'll be months getting back. What if they land in the sea? The desert? On top of a mountain? Vastly different conditions, and the only common way of utilising energy and self-replicating in all those places that we know of is by photosynthesis (or by consuming things that photosynthesise). You can maybe, maybe, make graphene out of carbon dioxide in the air, but even that's banking on it being there in the first place, and isn't applicable to every body you're going to end up on.

So your nanobots aren't going to be much "better" at consuming entire planets than photoplankton. They're subject to pretty much the same limitations, except perhaps less predation.

There is very little energy that is readily usable in deep space, i suppose you could take a fusion reactor to a place in deep space where the was alot of hydrogen and deuterium. Your solar panels would not even last the travel time between two useful output sources. You would have to either create perfect storage for the panels or manufacture them when you arrive at you destination. 

I could see a situation where the nanobots collect dust particles and separate them into metals, that can then be used to build stuff, however not really clear on a reason for doing this in deep space, the fusion reactor itself decays rather rapidly from nuetron radiation. Its not clear that any non-gravitational system coukd sustain energy output in deep space. 

[SomeGuy123]

12 hours ago, Jouni said:

A living cell doesn't self-replicate in the sense a Von Neumann machine would. It lives in an ecosystem much more complex than the cell itself, and receives highly refined materials from the ecosystem. Remove the ecosystem and the materials, and the cell can't replicate anymore.

When we're talking about Von Neumann machines, we're talking about systems with no known precedent in the universe.

Finally.  You make a statement that is 100% factually wrong.  No way to wiggle out of this one.  Perhaps you can use this new knowledge to fix your math.

E-coli need 3 things to replicate : water, sugar, oxygen, and certain trace elements.  These trace elements are not highly refined, it just means there's a tiny amount of dissolved metals in the water.   The bacterium itself is a completely self contained machine able to manufacture every internal part : it just needs the sugar for the energy to do it, and the oxygen to oxidize the sugar, and it needs metals because certain key enzymes use iron and other metals in key places.  It has slightly under 30k total unique mechanical parts.

Algae needs even less : like e-coli but skip the sugar and net dissolved oxygen (they need some at night), swap in sunlight and CO2 instead.

I've personally seen this for myself.  That's all that it takes.  You can fit a self contained ecosystem into a marble exposed to sunlight - the reason why it won't run forever has to do with DNA replication errors only.  There is no physical reason, it's just that if you only take a small sample of, say, algae and microscopic shrimp and cram them into a marble sized sphere, eventually random mistakes means the genetics of the small sample in that sphere will "drift" and stop working.  Make the pool bigger, and there are enough copies of the genes that this won't happen.  This is why a space-based von neumann machine has to have much better error correction systems than what DNA uses.

A von neuman space machine is a machine that could contain the machine phase version of e-coli, where it just needs a gaseous form of carbon, iron, etc as feedstocks.  It would need sunlight as well.  Like e-coli, it would have a protective cell membrane to protect the internals of the machine from the outside environment - the membrane just has to be thicker to protect against vacuum and dust and some micrometeorites.  You know the drill.  Like bacteria capable of making spores, the machine would be fairly inactive when it is not actually attached to a planet or asteroid or something containing matter it can eat.  

Edited December 12, 2015 by SomeGuy123

[SomeGuy123]

12 hours ago, Jouni said:

My main assumption is that physics can be described, simulated, and understood. If that's true, the universe is equivalent to a Turing machine, and many things turn out to be logically / information-theoretically / statistically impossible and/or computationally infeasible. If your claims are incompatible with these theories, the claims are wrong, you're abandoning basic logic, or you're saying that the laws of physics can't be described. You can't ignore the fundamental laws of logic and nature just because you don't know them.

I'm not the one who has a theory that is incompatible with known scientific facts.   Aim those criticisms at your own theory : a turing machine is a simple, "toy" model created a mere 50 years ago.  It seems the height of arrogance to start with the assumption that it applies to the universe.  (I'd start with the assumption that it doesn't until proven otherwise)

[SomeGuy123]

12 hours ago, Jouni said:

A living cell doesn't self-replicate in the sense a Von Neumann machine would. It lives in an ecosystem much more complex than the cell itself, and receives highly refined materials from the ecosystem. Remove the ecosystem and the materials, and the cell can't replicate anymore.

When we're talking about Von Neumann machines, we're talking about systems with no known precedent in the universe.

I have a couple more insights into this.  I personally, IRL, while I majored in biology, I currently work on embedded electronic systems.  These are very close to von neuman machines in their purest form - The machines start up reading a binary "tape" of onboard flash memory and always operate per a very simple set of control variables stored somewhere on that tape.

I've encountered one of the problems you are talking about - I wanted to test an external flash memory chip while the whole machine was inside an oven.  So the machine starts up, runs a pseudorandom function, and wrote pseudorandom values to each memory address on the chip in sequence.  So far so good.

Well, due to a glitch, I didn't have it working for a while and then it appeared to work.  But it wasn't working.  See, every time the embedded system started, it would try to write to the external flash a random number, increment address, write again, and so on.  After each write it would read the flash at that location.

So a glitch caused the flash module to become "unlocked" and it wrote just one time this "random" sequence.

Every test I did after that, it "passed".  Actually, it wasn't writing anything as I had not issued to unlock sequence, and so every write was failing, but the test was passing because every value it read was what it expected to see.

I fixed this crudely by having it accept a keystroke from a host computer and using the value that happened to be inside an onboard timer at that time to seed the RNG.  Problem solved.

Well, an e-coli can be thought of as a turing machine - it literally reads a tape encoded in base-4 called DNA - but it also has external inputs from the environment.  All kinds of external sensors.  So the e-coli's state doesn't just depend on the internal tape but a pseudorandom sequence of environmental signals.  

Another issue you are missing is that random signals from the environment don't actually contain much information, but survival in this universe is itself information.  So a population of e-coli, the turing machines that are "programmed correct" survive and the halted ones don't.  This is a very strong, information rich external signal, apparently, which is why we are able to have this debate.  

So this is why space ones made by humans would work.  Your mental model is wrong because the turing machine doesn't just depend on internal state on it's memory, it also depends on what it happens to see through onboard sensors and telescopes, picking up information from the star it is trying to survive at.  It also may fail to survive, which means over a population of these machines, the ones that happen to arrive at the right internal states survive and the frozen ones don't/

[PB666]

1 hour ago, SomeGuy123 said:

Finally.  You make a statement that is 100% factually wrong.  No way to wiggle out of this one.  Perhaps you can use this new knowledge to fix your math.

E-coli need 3 things to replicate : water, sugar, oxygen, and certain trace elements.  These trace elements are not highly refined, it just means there's a tiny amount of dissolved metals in the water.   The bacterium itself is a completely self contained machine able to manufacture every internal part : it just needs the sugar for the energy to do it, and the oxygen to oxidize the sugar, and it needs metals because certain key enzymes use iron and other metals in key places.  It has slightly under 30k total unique mechanical parts.

Algae needs even less : like e-coli but skip the sugar and net dissolved oxygen (they need some at night), swap in sunlight and CO2 instead.

I've personally seen this for myself.  That's all that it takes.  You can fit a self contained ecosystem into a marble exposed to sunlight - the reason why it won't run forever has to do with DNA replication errors only.  There is no physical reason, it's just that if you only take a small sample of, say, algae and microscopic shrimp and cram them into a marble sized sphere, eventually random mistakes means the genetics of the small sample in that sphere will "drift" and stop working.  Make the pool bigger, and there are enough copies of the genes that this won't happen.  This is why a space-based von neumann machine has to have much better error correction systems than what DNA uses.

A von neuman space machine is a machine that could contain the machine phase version of e-coli, where it just needs a gaseous form of carbon, iron, etc as feedstocks.  It would need sunlight as well.  Like e-coli, it would have a protective cell membrane to protect the internals of the machine from the outside environment - the membrane just has to be thicker to protect against vacuum and dust and some micrometeorites.  You know the drill.  Like bacteria capable of making spores, the machine would be fairly inactive when it is not actually attached to a planet or asteroid or something containing matter it can eat.  

E. coli is a facultative anaerobe, it does not need oxygen. This means that some bacteria will die in the presence of oxygen without free-oxide scavengers (e.g clostridium) e. coli can survive with oxygen and a limited numbervof oxide free radicals present. Free radicals are created from ozone, peroxides etc

[SomeGuy123]

23 minutes ago, PB666 said:

E. coli is a facultative anaerobe, it does not need oxygen. This means that some bacteria will die in the presence of oxygen without free-oxide scavengers (e.g clostridium) e. coli can survive with oxygen and a limited numbervof oxide free radicals present. Free radicals are created from ozone, peroxides etc

The rest of what I said is correct, right?  There just has to be roughly the right amount of metal, within a fairly wide range, and something it can eat, right?

[Spaceception]

If we made Von Nuemann probes, we'd need to program them not to replicate themselves on anything that has/very likely has life on it. We'd also need to program them to only replicate themselves a certain number of times so they don't get out of control. And finally, we'd need to put them in a system with a Gas giant with likely moons so they could spread out easier, once we've figured all of that out, we can have nano-machines exploring the Galaxy!

[Jouni]

10 hours ago, SomeGuy123 said:

I'm not the one who has a theory that is incompatible with known scientific facts.   Aim those criticisms at your own theory : a turing machine is a simple, "toy" model created a mere 50 years ago.  It seems the height of arrogance to start with the assumption that it applies to the universe.  (I'd start with the assumption that it doesn't until proven otherwise)

A Turing machine is not a "toy model". It's a central concept in mathematical logic and theoretical computer science. It was described around 80 years ago precisely as a universal formalism capable of simulating any other machine, procedure, or system. Its original purpose was to prove that there is no procedure that can always determine, whether a logical statement is true or false.

9 hours ago, SomeGuy123 said:

Well, an e-coli can be thought of as a turing machine - it literally reads a tape encoded in base-4 called DNA - but it also has external inputs from the environment.  All kinds of external sensors.  So the e-coli's state doesn't just depend on the internal tape but a pseudorandom sequence of environmental signals.  

This changes nothing. A single-tape Turing machine is computationally equivalent to a Turing machine that has 10^10^10 additional tapes, each of them infinite in 10^10^10 dimensions and containing random input.

9 hours ago, SomeGuy123 said:

E-coli need 3 things to replicate : water, sugar, oxygen, and certain trace elements.  These trace elements are not highly refined, it just means there's a tiny amount of dissolved metals in the water.   The bacterium itself is a completely self contained machine able to manufacture every internal part : it just needs the sugar for the energy to do it, and the oxygen to oxidize the sugar, and it needs metals because certain key enzymes use iron and other metals in key places.  It has slightly under 30k total unique mechanical parts.

Algae needs even less : like e-coli but skip the sugar and net dissolved oxygen (they need some at night), swap in sunlight and CO2 instead.

Can you find the conditions where E. coli or algae can replicate themselves clearly outside any ecosystem? Or do those machines only replicate, because a vastly more complex machine provides them with just the right conditions to do so?

A Von Neumann machine must be able to replicate without such assistance. The real question is, is such replication possible, when the machine itself is the most complex system around.

[Dispatcher]

Its simple:  we just deprive them of lysine.  

[KSK]

On 12 December 2015 10:56:35, Jouni said:

Can you find the conditions where E. coli or algae can replicate themselves clearly outside any ecosystem? Or do those machines only replicate, because a vastly more complex machine provides them with just the right conditions to do so?

 

Yes. Or I can for cyanobacteria, aka blue-green algae, which I suspect are what SomeGuy123 had in mind. I have no reason to doubt what SomeGuy123 is saying about culturing E. coli but I would have thought they would need a source of nitrogen and phosphorus as a bare minimum over sugar, air and trace metals.

Cyanobacteria can live just about anywhere. From the Wikipedia page:

"Cyanobacteria can be found in almost every terrestrial and aquatic habitat—oceans, fresh water, damp soil, temporarily moistened rocks in deserts, bare rock and soil, and even Antarctic rocks. They can occur as planktonic cells or form phototrophic biofilms. They are found in almost every endolithic ecosystem.^[9] A few are endosymbionts in lichens, plants, various protists, or sponges and provide energy for the host. Some live in the fur of sloths, providing a form of camouflage.^[10]"

They can fix atmospheric CO2 as a carbon source. They can fix atmospheric N2 as a nitrogen source. I presume they require some source of water (no matter how marginal) as a source of oxygen and hydrogen. On top of that they'll need a source of phosphorus (which is a limiting nutrient for most organisms) and then probably sulphur and other trace elements. These are all available from the environment - there is no need to postulate a vastly more complicated ecoystem for cyanobacteria to replicate within. In fact, I would imagine (without any citations to back this up) that cyanobacteria were the amongst the very first organisms responsible for taking 'a bare lump of sea and rock, girt all about with clouds' and transforming that into the 'vastly more complex machine' that you refer to.

The same would be true, I think, of a von Neumann machine. It will require an appropriate environment - probably a carbonaceous chondrite or something with enough chemical diversity to provide the necessary raw materials for replication. It will not require a complex ecosystem finely-tuned to support that replication.

 

[Jouni]

2 hours ago, KSK said:

They can fix atmospheric CO2 as a carbon source. They can fix atmospheric N2 as a nitrogen source. I presume they require some source of water (no matter how marginal) as a source of oxygen and hydrogen. On top of that they'll need a source of phosphorus (which is a limiting nutrient for most organisms) and then probably sulphur and other trace elements. These are all available from the environment - there is no need to postulate a vastly more complicated ecoystem for cyanobacteria to replicate within.

They're available from an environment, which has supported a vast and complex ecosystem for billions of years. I specifically asked for an environment that has not been affected by any life on the Earth to any significant degree.

My entire point was that environments capable of supporting replication don't seem to occur naturally, except when there is a complex system maintaining them. Without such a system, they will probably degenerate towards a state of higher entropy, where they can no longer support replication. Or at least that's my intuition, and that's why I asked for counterexamples.

[KSK]

Well in that case you're asking for the impossible because we have exactly one example to work with and that verifiably has been affected by life for on the Earth (being as it is the Earth) by a significant degree. If that's your requirement for proof, we're wasting our time here. Myself and SomeGuy123 have specifically pointed out an organism that can subsist on simple inorganic materials and would be capable of subsisting on those materials regardless of where they're found and any other prevailing environmental conditions. A complex system is not required and I would be quite prepared to bet that we could take a suitable terrestrial cyanobacteria to Mars and that it would flourish.

Your 'chicken-and-egg' premise that replication doesn't occur naturally except where there is a complex system supporting it is, I think, wrong. Taking the only system we know as an example; once a replicating system arises, it necessarily changes its environment to make it more favourable for other such systems to arise. For very simple replicators, I can imagine 'dead' (whatever that means in this context) replicators releasing parts of themselves into the environment thus providing a source of more refined materials for other replicating systems to start with. Once we get to a replicator that uses phosphorus in some way (for metabolism, storing information or whatever) then we have something that is capable of dramatically accelerating the phosphorus cycle, increasing the availability of this vital nutrient for other replicators.

Complexity of environment and complexity of replicators increase in lockstep. Logically though, at some point there has to be a transition point from 'environment without a replicator' to 'environment with a replicator'. By definition that environment arose naturally because there was no other way it could have arisen. Unless of course we're straying into sci-fi or religion and assume that the Earth was specially set up to support life by an outside agency, but I think that's outside the scope of our discussion.

[Jouni]

8 hours ago, KSK said:

Well in that case you're asking for the impossible because we have exactly one example to work with and that verifiably has been affected by life for on the Earth (being as it is the Earth) by a significant degree.

 That was the point. There is no evidence that environments capable of supporting life do occur outside ecosystems. Therefore living organisms do not provide any evidence for the claim that Von Neumann machines are possible.

8 hours ago, KSK said:

Your 'chicken-and-egg' premise that replication doesn't occur naturally except where there is a complex system supporting it is, I think, wrong. Taking the only system we know as an example; once a replicating system arises, it necessarily changes its environment to make it more favourable for other such systems to arise.

Obviously living organisms and the environment supporting them have evolved and continue evolving together. The key point was that they don't occur separately. You probably can't find an environment capable of supporting any particular kind of life, except where similar life has already evolved by random chance.

[KSK]

1 hour ago, Jouni said:

Obviously living organisms and the environment supporting them have evolved and continue evolving together. The key point was that they don't occur separately. You probably can't find an environment capable of supporting any particular kind of life, except where similar life has already evolved by random chance.

Right - so how did that other, similar life arise? At some point you need to have abiogenesis, that is, living (thus replicating) systems arising from non replicating precursors. 

Now it might be that Earth is the only planet where this has happened. Given the size of the Universe, I think this is spectacularly unlikely but nevertheless, Earth might have provided that one special environment.

But for our purposes, that doesn't matter. Earth provides the one key example that we need which demonstrates that replicating systems can arise from non replicating systems. It might be improbably unlikely, we might never figure out a way of doing it synthetically (aka build a von Neumann machine). However, it is quite obviously not physically impossible - else we wouldn't be here arguing about it.

[Jouni]

16 hours ago, KSK said:

Right - so how did that other, similar life arise? At some point you need to have abiogenesis, that is, living (thus replicating) systems arising from non replicating precursors.

1. Ecosystems developed as a result of random processes.
2. Ecosystems may mix, expand, and become more complex, but they don't self-replicate. At least we don't have any evidence for their replication.
3. Individual organisms replicate within ecosystems, but because they're not self-contained systems, they're not self-replicating in the sense of Von Neumann machines.

So, essentially, ecosystems are the primary systems, while living organisms are just subsystems that can't survive without the complete system. When we're debating whether Von Neumann machines are possible, the relevant question is whether ecosystems can replicate themselves.

[KSK]

What? We've got some back-to-front definitions here. An ecosystem is the sum of the different living organisms in a given area, their interactions with each other and the interactions with their environment. Living organisms and the environment itself are the primary systems, an ecosystem is an emergent system created by the interactions between those primary systems. Ecosystems can be large, small, or even nested. A coral reef would qualify as an ecosystem - existing within the much larger ecosystem provided by the Earth as a whole.

Take a living organism out of its ecosystem and it may or may not survive. Organisms at the bottom of the food chain will probably survive quite handily - see my earlier comment about cyanobacteria on Mars, unless their new environment is utterly inimical.They survive precisely because they're at the bottom of the food chain and so by definition are not dependent on other organisms for survival. Organisms further up the food chain do (again by definition) depend on other organisms for survival (at a very basic level, they eat them) and so, taken out of their ecosystem, will not survive.

For each of your points:

1.  Correct - but only in the sense that individual organisms arose through random processes and then aggregated into ecosystems.

2.  Not entirely correct. A coral reef is an ecosystem. A lichen is an ecosystem (albeit a relatively simple one) comprising a fungus, an algae and/or a cyanobacteria. Both are quite capable of self-replication.

3. No organism (or von Neumann machine) is entirely self contained. To do anything meaningful such as move or replicate, they're going to need energy and materials from their environment. However, as discussed above, some organisms are far more self contained than others.

Edited December 15, 2015 by KSK

[Bill Phil]

Except it's not a chain. It's a web. And even if it were a chain, decomposers are at the top and bottom.

[Jouni]

36 minutes ago, KSK said:

What? We've got some back-to-front definitions here. An ecosystem is the sum of the different living organisms in a given area, their interactions with each other and the interactions with their environment. Living organisms and the environment itself are the primary systems, an ecosystem is an emergent system created by the interactions between those primary systems. Ecosystems can be large, small, or even nested. A coral reef would qualify as an ecosystem - existing within the much larger ecosystem provided by the Earth as a whole.

The primary system depends on the context. When the question in hand is whether a self-contained system can possibly self-replicate in a nontrivial fraction of all solar systems, the ecosystem is obviously the primary system. It's self-contained, while a living organism is not. And by "ecosystem", I mean something like "the transitive closure of the ecosystem", because we're talking about self-contained systems. Under this definition, the Earth probably has only one ecosystem.

36 minutes ago, KSK said:

Take a living organism out of its ecosystem and it may or may not survive. Organisms at the bottom of the food chain will probably survive quite handily - see my earlier comment about cyanobacteria on Mars, unless their new environment is utterly inimical.They survive precisely because they're at the bottom of the food chain and so by definition are not dependent on other organisms for survival. Organisms further up the food chain do (again by definition) depend on other organisms for survival (at a very basic level, they eat them) and so, taken out of their ecosystem, will not survive.

By "survival", I meant being able to reproduce and to establish a stable/growing population. Remember that the context is von Neumann machines, and the meaning of every word must be understood against that context.

36 minutes ago, KSK said:

3. No organism (or von Neumann machine) is entirely self contained. To do anything meaningful such as move or replicate, they're going to need energy and materials from their environment. However, as discussed above, some organisms are far more self contained than others.

This is again context-dependent. A living organism is self-contained within the context of its ecosystem. Take an organism and place it elsewhere in the (local, not the transitive closure one) ecosystem, and it will probably survive, thrive, and reproduce.

In this case, the context is the galaxy. We're talking about self-contained systems capable of moving from one solar system into another and self-replicating upon reaching the destination. I've essentially claimed that the galactic "ecosystem" doesn't look complex enough to support such self-replication.

[KSK]

Fine - it's a web. I referred to a chain because it's conceptually simpler and the distinction between the two was irrelevant for my argument. In any case, presumably your decomposers are decomposing other organisms? In which case they are not at the bottom since they're feeding on other organisms.

[Bill Phil]

11 minutes ago, KSK said:

Fine - it's a web. I referred to a chain because it's conceptually simpler and the distinction between the two was irrelevant for my argument. In any case, presumably your decomposers are decomposing other organisms? In which case they are not at the bottom since they're feeding on other organisms.

But they are responsible for the plants having the resources they need. Making the chain circular. We eat plants. We eventually die. Our bodies are decomposed. The resources released by the decomposers go to the plants. The decomposers "eat" us, and release useful nutrients that are consumed.

[KSK]

1 hour ago, Bill Phil said:

But they are responsible for the plants having the resources they need. Making the chain circular. We eat plants. We eventually die. Our bodies are decomposed. The resources released by the decomposers go to the plants. The decomposers "eat" us, and release useful nutrients that are consumed.

Yes - but there are other organisms (e.g. the cyanobacteria that I keep banging on about) that don't need the resources released by the decomposers.