How likely is it that a Von Neumann machine destroys the Earth?

[YogSosoth]

Self-replicating machines, often shown in sci-fi as tiny nanobots that break down various elements to recreate itself, kind of like a mechanical virus, seems like it would be doable in the next century or two.

I've heard rumblings about tiny machines over the last few years, and while its not at nano-sized levels yet, we can make and program increasing tinier and tinier stuff. Even back in the 80's, when Disco was danced to unironically for pleasure within living memory, people were theorizing using tiny robots to repair cells and stuff. Of course, robots in the 80's would look blocky and combine into a bigger robot, but the point is that it wasn't just science fiction, it was soon-to-be reality.

What would prevent just one of these machines from replicating itself like HIV and just destroy the earth? I'm thinking that probably, the programming would not be so sophisticated to make it fool proof. Eventually the machine's going to run into a situation or an element that will slow it down or stop it, and buy us time to nuke it into oblivion.

Another thing that might prevent such a catastrophe is the lack of materials. Its fine in sci-fi to theorize that these machines can break any element down into component parts and repurpose them as materials to build itself, but we can't even create believable AI yet to fool computer users. There's no way to account for the myriad of possibilities when sending a billion or trillion tiny machines out into the real world, to be bombarded by countless stimuli and expect them to survive and replicate itself, can it? And how would it even program itself?

Another thing is energy. What's powering these little guys? I can't imagine that a machine that's expected to practically deconstruct and reconstruct the molecular structure of an molecule is going to be powered by fossil fuels, or a tiny plug going into an outlet. We'd have to engineer actual living cells that runs on sunlight for that to happen and I think that is so far away from what we can do its not worth worrying about.

[CalMeacham]

I'd never heard anyone suggest that space probe Von Neumann machines would be nanobots. In fact, I can't see any good reason they would be. Any SF I've read assumed that such devices would be large and complex devices. I suspect any real-life speculation would assume the same, although I admit I haven't read any such pieces.

[YogSosoth]

Originally Posted by CalMeacham

I'd never heard anyone suggest that space probe Von Neumann machines would be nanobots. In fact, I can't see any good reason they would be. Any SF I've read assumed that such devices would be large and complex devices. I suspect any real-life speculation would assume the same, although I admit I haven't read any such pieces.

I think the black cloud in the remake of the Day the Earth Stood Still were tiny nanobots. I've also read it in this older website that I can't remember the name of, it lists possible ways the earth, or the universe, can be destroyed. The black goo that tiny robots turns us into was one possibility.

All it takes is one, which is why its so scary. Somebody makes it, then accidentally drops it on the floor, and the earth is doomed

[CalMeacham]

If so, that's a new twist on the old idea. I think large complex vion Neuman machines are more likely than nanobots. In the remake of TDTESS, after all, the nanobots didn't get here all by themselves, but were brought by an intelligent being piloting a ship.

And they weren't extremely "nano" -- they were visible things that looked like indects.

[jackdavinci]

The technology required for an apocalyptic level disaster is so advanced, that it would require many intermittent levels of improvements, each of which in turn would have its own safeguards developed.

[Machine Elf]

Originally Posted by YogSosoth

Self-replicating machines, often shown in sci-fi as tiny nanobots that break down various elements to recreate itself, kind of like a mechanical virus, seems like it would be doable in the next century or two.

I've heard rumblings about tiny machines over the last few years, and while its not at nano-sized levels yet, we can make and program increasing tinier and tinier stuff. Even back in the 80's, when Disco was danced to unironically for pleasure within living memory, people were theorizing using tiny robots to repair cells and stuff. Of course, robots in the 80's would look blocky and combine into a bigger robot, but the point is that it wasn't just science fiction, it was soon-to-be reality.

What would prevent just one of these machines from replicating itself like HIV and just destroy the earth? I'm thinking that probably, the programming would not be so sophisticated to make it fool proof. Eventually the machine's going to run into a situation or an element that will slow it down or stop it, and buy us time to nuke it into oblivion.

Another thing that might prevent such a catastrophe is the lack of materials. Its fine in sci-fi to theorize that these machines can break any element down into component parts and repurpose them as materials to build itself, but we can't even create believable AI yet to fool computer users. There's no way to account for the myriad of possibilities when sending a billion or trillion tiny machines out into the real world, to be bombarded by countless stimuli and expect them to survive and replicate itself, can it? And how would it even program itself?

Another thing is energy. What's powering these little guys? I can't imagine that a machine that's expected to practically deconstruct and reconstruct the molecular structure of an molecule is going to be powered by fossil fuels, or a tiny plug going into an outlet. We'd have to engineer actual living cells that runs on sunlight for that to happen and I think that is so far away from what we can do its not worth worrying about.

All of this is discussed under the heading "gray goo scenario," in which nanobots consume the matter of the world and use it replicate themselves until there is nothing left but themselves, forming a mass of gray goo.

[Ethilrist]

Probably not suited for GQ, but my favorite treatment of nanotechnology in fiction (The Silver Age(?)) posited a few problems with the "gray goo" issue, the main one being power: all those little robots gotta run on something, and if one of them goes out and creates a robot, the new robot has to get its power from something (probably the first robot...), so eventually, absent access to nano-scaled zero-point-energy power sources, there is a finite number of iterations of nanobot before you start creating dead robots, which aren't too helpful at taking over the world.

[Trinopus]

In SF, John T. Sladek had a *hilarious* spoof on the idea in his book "The Reproductive System." The system gets out of control, with entirely unpredictable results.

He also deals with the power issue...

One or two more serious SF writers have also mentioned the waste-heat issue. Machines produce heat, and tiny machines have fewer ways to dump that accumulated heat.

Still, as "nightmare" scenarios go, it's a bit more believable than zombies...

[Der Trihs]

It's my understanding that these days the consensus is that an accidental grey goo event can be prevented fairly easily; the real danger is someone doing so on purpose. "Do what we say or we kill the world" would have obvious appeal to terrorists and other fanatics.

Originally Posted by YogSosoth

I'm thinking that probably, the programming would not be so sophisticated to make it fool proof.

Making the programing dumb and inflexible is in fact one of the proposed safeguards IIRC.

Originally Posted by YogSosoth

Another thing that might prevent such a catastrophe is the lack of materials. Its fine in sci-fi to theorize that these machines can break any element down into component parts and repurpose them as materials to build itself, but we can't even create believable AI yet to fool computer users. There's no way to account for the myriad of possibilities when sending a billion or trillion tiny machines out into the real world, to be bombarded by countless stimuli and expect them to survive and replicate itself, can it?

Living cells manage, so obviously it's doable. And part of the idea behind such nanobots is that since they are working with interchangeable atoms they don't need to be as smart as something dealing with the more variable macroscopic world.

On the other hand, one of the proposed safeguards is to simply make such replicators at least partly out of rare elements. If what it needs to replicate simply isn't there, then it just can't replicate.

Another is to make them only able to function under exotic conditions; replicators that only operate at liquid nitrogen temperatures obviously can't eat the Earth. This trick won't work with cell-repair nanomachines though.

Originally Posted by Ethilrist

Probably not suited for GQ, but my favorite treatment of nanotechnology in fiction (The Silver Age(?)) posited a few problems with the "gray goo" issue, the main one being power: all those little robots gotta run on something, and if one of them goes out and creates a robot, the new robot has to get its power from something (probably the first robot...), so eventually, absent access to nano-scaled zero-point-energy power sources, there is a finite number of iterations of nanobot before you start creating dead robots, which aren't too helpful at taking over the world.

They can power themselves by consuming available energy sources - like organic tissue - and sunlight. So they probably wouldn't eat the whole planet, just the surface. But since we'd be one of the things eaten that's not much consolation...

[si_blakely]

Obligatory XKCD explains why most of the earth is safe from runaway nanobots.

[si_blakely]

Related to the power issue - how do nanoscale machines disassemble stable materials - silicates are very stable and hard to pull apart. Even at a molecular level pulling the silicon away will be hard, and you have to avoid the Oxygen as a reactive byproduct.

[Alessan]

Originally Posted by CalMeacham

I'd never heard anyone suggest that space probe Von Neumann machines would be nanobots. In fact, I can't see any good reason they would be. Any SF I've read assumed that such devices would be large and complex devices. I suspect any real-life speculation would assume the same, although I admit I haven't read any such pieces.

You can build a large, complex machine out of microscopic machines - sort of like an organism being constructed out of cells. A Von Neumann probe in particular needs to be both self-repairing and self-replicating, both of which are qualities typical of living organisms.

[Der Trihs]

They could just use carbon instead, just as living things do. Assuming the designers want it to be easy for them to replicate of course.

[Chronos]

If you want to destroy the planet itself, there's no way. I don't know what the replicators would be made of, but it almost certainly includes a lot of things other than iron and nickle, so they'd run out of suitable raw materials rather quickly.

If you just mean that the self-replicating machines replicate far enough to ruin the ecosystem and make the planet uninhabitable for most life forms, that's not only possible, but has happened many times in the planet's history.

[Ethilrist]

Originally Posted by si_blakely

Related to the power issue - how do nanoscale machines disassemble stable materials - silicates are very stable and hard to pull apart. Even at a molecular level pulling the silicon away will be hard, and you have to avoid the Oxygen as a reactive byproduct.

That'd be another thing from the book I mentioned--nano-assembly required (a) near-vaccuum, to keep all those pesky atmospheric things from getting in the way and (b) effectively pure materials, at the atomic level. Both of which can be arranged in a self-contained Valu-Mart Nano Vendor, but up in a pine tree in the middle of the forest? Not so much.

[Der Trihs]

Originally Posted by Ethilrist

That'd be another thing from the book I mentioned--nano-assembly required (a) near-vaccuum, to keep all those pesky atmospheric things from getting in the way and (b) effectively pure materials, at the atomic level. Both of which can be arranged in a self-contained Valu-Mart Nano Vendor, but up in a pine tree in the middle of the forest? Not so much.

I doubt that would be necessary in a purely technological sense; as said, organic life is proof that replicators don't need that kind of thing. On the other hand, if you want safe replicators that you can use in such a "Valu-Mart Nano Vendor" without worrying that they'll run amok, those are good limitations to deliberately build into them.

[njtt]

The planet is already full of self replicating machines, honed for survival and self-replication at all costs. They are called living organisms. Some are very dangerous, but none have destroyed us yet.

Why should artificial self-replicators be any more effective or dangerous than the natural ones? Indeed, most likely any relatively recently created artificial one will be much less dangerous and much less effective at reproducing itself, because it has not been honed for the purpose by eons of natural selection. If it survives its early generations, and if its self-replicating mechanisms are of the right sort, it may become subject to natural selection itself, and thus become more efficient at survival and self-replication, and thereby more dangerous, but I see no reason why that would not just mean that it would find its niche in the ecosystem. Inasmuch as it survives and is dangerous it is in competition with other living things, and they will evolve defenses against it.

So, no, a Von Neumann machine is no more likely - actually less likely - to destroy the Earth than a marigold or a lemur or a smallpox virus.

[Senegoid]

Originally Posted by YogSosoth

I think the black cloud in the remake of the Day the Earth Stood Still were tiny nanobots. I've also read it in this older website that I can't remember the name of, it lists possible ways the earth, or the universe, can be destroyed. The black goo that tiny robots turns us into was one possibility.

Maybe this is the site you are thinking of? Top 10 Ways to Destroy the Earth, by LiveScience. Von Neumann machines is #2 (that is, 2nd-last) on the list. (Requires JavaScript to view.)

[Trinopus]

Originally Posted by njtt

The planet is already full of self replicating machines, honed for survival and self-replication at all costs. They are called living organisms. Some are very dangerous, but none have destroyed us yet. . . .

True, but they have totally changed the earth's atmosphere, building up oxygen levels to an absurd and highly toxic degree.

[Senegoid]

Originally Posted by njtt

Why should artificial self-replicators be any more effective or dangerous than the natural ones? Indeed, most likely any relatively recently created artificial one will be much less dangerous and much less effective at reproducing itself, because it has not been honed for the purpose by eons of natural selection. If it survives its early generations, and if its self-replicating mechanisms are of the right sort, it may become subject to natural selection itself, and thus become more efficient at survival and self-replication, and thereby more dangerous, but I see no reason why that would not just mean that it would find its niche in the ecosystem. Inasmuch as it survives and is dangerous it is in competition with other living things, and they will evolve defenses against it.

What kind place would a nanobot have in a biological ecosystem? Who will nanobots eat? Who/what will eat nanobots? Are they edible? What place, if any, would nanobots have in the food chain? Would various kinds of nanobots evolve, having an entire alternate food chain among themselves, separate and distinct from the "natural" organic food chain?

[Lemur866]

Originally Posted by njtt

So, no, a Von Neumann machine is no more likely - actually less likely - to destroy the Earth than a marigold or a lemur or a smallpox virus.

The danger of lemurs destroying the Earth has been vastly overinflated.

[lazybratsche]

That's exactly what you want us to think, isn't it?

[Der Trihs]

Originally Posted by njtt

Why should artificial self-replicators be any more effective or dangerous than the natural ones?

Because they could be made out of materials that natural organisms can't eat for one. They would also likely be more efficient, due to being rationally designed. And for another, the simple fact that they are a wholly new creation makes them dangerous; evolved creatures tend not to deal well with incursions by species that evolved outside the local ecosystem. Something that isn't even our kind of life is going to be even harder to deal with.

Originally Posted by njtt

Indeed, most likely any relatively recently created artificial one will be much less dangerous and much less effective at reproducing itself, because it has not been honed for the purpose by eons of natural selection.

On the contrary, the fact that natural organisms have been shaped by evolution makes them less likely to be as efficient as possible at reproducing themselves. First, because an evolved organism is a collection of kludges, a Rube Goldberg machine accumulated over millions of years. And second because reproducing as efficiently as possible isn't typically the best reproductive strategy, given how doing so tends to destroy your own food sources and result in a later population crash.

[AaronX]

Well, there is that danger from subatomic particles. http://en.wikipedia.org/wiki/Strangelet
a particle called a "strangelet" might convert normal matter into more strangelets on contact.

Also you may be interested in reading about ice 9, seeing no one has brought it up. http://en.wikipedia.org/wiki/Ice-nine

[Mangetout]

The danger of making them out of specific rare materials, or to operate only under specific conditions. Is that these are replicators - almost certainly *imperfect* replicators. They'll evolve.

[Der Trihs]

Originally Posted by Mangetout

The danger of making them out of specific rare materials, or to operate only under specific conditions. Is that these are replicators - almost certainly *imperfect* replicators. They'll evolve.

Not unless you design them with the ability. Unless specifically designed to be capable of evolution, things created by a human-style design process don't evolve when replicated imperfectly; they just break. The only reason that the ability to evolve is so universal to organic life is because it all comes from ancestors that could evolve.

[FasterThanMeerkats]

But what if the nanobot was also a bending unit?

[Der Trihs]

Originally Posted by FasterThanMeerkats

But what if the nanobot was also a bending unit?

Well duh, we'd placate it with liquor and nanohookerbots.

[Mijin]

Originally Posted by Trinopus

True, but they have totally changed the earth's atmosphere, building up oxygen levels to an absurd and highly toxic degree.

Yeah but that was hardly one species completely sweeping the earth overnight. It was the collective effect of many species of photosynthesizing cyanobacteria operating over at least 200 million years.

[Mangetout]

Originally Posted by Der Trihs

Not unless you design them with the ability. Unless specifically designed to be capable of evolution, things created by a human-style design process don't evolve when replicated imperfectly; they just break. The only reason that the ability to evolve is so universal to organic life is because it all comes from ancestors that could evolve.

Human -designed things (physical ones, at least) don't self-replicate at the moment, so there isn't a good example to point out - but it's simply untrue to say that they 'Just break' and stop functioning - some things, especially complex ones, malfunction and produce unintended output when they break.

Something as small as a nanobot would be subject to random modification from stray cosmic rays, etc. It's not so much that we would need or choose to design a imperfect replicator, it's more that we are probably incapable of designing a completely perfect one - thus, evolution may well happen anyway, regardless of our design, or wishes.

[Quercus]

Originally Posted by Der Trihs

On the contrary, the fact that natural organisms have been shaped by evolution makes them less likely to be as efficient as possible at reproducing themselves. First, because an evolved organism is a collection of kludges, a Rube Goldberg machine accumulated over millions of years. And second because reproducing as efficiently as possible isn't typically the best reproductive strategy, given how doing so tends to destroy your own food sources and result in a later population crash.

You're kind of arguing both ways, here. I'll grant that it's quite possible a designed nanobot is more effective than a given bacteria; there is indeed nothing magical about natural selection. But that 'nothing magical' particularly applies to the second part of your statement: reproducing efficiently is always the best strategy and what natural selection will get as close to as possible. A bacteria that's in a resource-rich environment and holds off on reproducing will get out-competed by ones that reproduce as fast and efficiently as possible. Sure, if the resources run out the population will crash, but the remaining population will be drawn from the quick reproducers. And of course, if resources are limited, the population is going to be small in the long run anyway, so it really makes no difference whether it's quickly after a big population , or a little later with no big spike in population.

And of course, the real world is full of examples of populations that grow quickly consuming a limited resource and then crash.

[Chronos]

Not unless you design them with the ability. Unless specifically designed to be capable of evolution, things created by a human-style design process don't evolve when replicated imperfectly; they just break. The only reason that the ability to evolve is so universal to organic life is because it all comes from ancestors that could evolve.

The vast majority of time, when a self-replicator replicates imperfectly, it breaks. This is just as true of the already-existing kind as of the ones we could make. All it takes for evolution is for, once in a very great while, one to replicate imperfectly and not break.

[eburacum45]

Nanobots or, more probably microbots on a similar scale to bacteria would be only part of the action. They could be manufactured by larger machines that are resistant to evolution thanks to error-checking. The small-scale devices could be as incapable of self-replication as red blood cells, but just as indispensable for the growth and self-replication of the entire system.

Evolution is not inevitable in a correctly designed self-replicating system - the data management (artificial genetics) could be designed to check for errors using ECC and to eliminate them. In theory devices could be built that do not mutate for billions of years.

[eburacum45]

Robert Bradbury devised a scheme to use self-replicating systems to destroy the whole Earth, not just its biosphere.

First you have to destroy Mercury, using the power of the Sun and self-replicating machines that strip the surface of that small planet and convert it into orbiting solar-power collectors. If fully dismantled Mercury could intercept a large fraction of the Sun's output. These collectors would transmit power to a second set of self-replicating systems, which do the same thing to Earth. Dismantling Mercury first isn't entirely necessary, but the extra power it makes available would speed things up considerably.

I suppose dismantling the Moon first would help as well, seeing as it is handy.

Although this is not perhaps the best use of the earth and its resources, it might be just the ticket in a colony solar system where there are no inhabitable planets; a family of inhospitable planets could be dismantled and turned into artificial habitats or a matrioshka brain.

[Mangetout]

Originally Posted by eburacum45

Nanobots or, more probably microbots on a similar scale to bacteria would be only part of the action. They could be manufactured by larger machines that are resistant to evolution thanks to error-checking. The small-scale devices could be as incapable of self-replication as red blood cells, but just as indispensable for the growth and self-replication of the entire system.

Evolution is not inevitable in a correctly designed self-replicating system - the data management (artificial genetics) could be designed to check for errors using ECC and to eliminate them. In theory devices could be built that do not mutate for billions of years.

Agreed, design can minimise or provide resistance to mutation.

But DT's assertion that mutation would have to be designed-in is not correct.

[TriPolar]

Instead of evolution nanobots could be designed to combine to make more variable macrobots. However, any way it's done, the bots wouldn't be much more effective than humans at changing the earth. They'll run out of resources just as quickly as we do. If they want to destroy mankind killing humans by infection will be the simplest route.

[James52637]

Originally Posted by YogSosoth

[url="http://en.wikipedia.org/wiki/Self-replicating_machine"]

Another thing is energy. What's powering these little guys? I can't imagine that a machine that's expected to practically deconstruct and reconstruct the molecular structure of an molecule is going to be powered by fossil fuels, or a tiny plug going into an outlet. We'd have to engineer actual living cells that runs on sunlight for that to happen and I think that is so far away from what we can do its not worth worrying about.

http://online.wsj.com/article/SB10001424052748703559004575256470152341984.html

*cough cough*

[Mijin]

Originally Posted by TriPolar

If they want to destroy mankind killing humans by infection will be the simplest route.

Depends what you mean by destroy.

Infections can wipe out species that are already on the brink of extinction. But a widely-dispersed species with 7 billion individuals, not so much. That's just based on natural variation, leave aside that humans will apply their technology to fight it, alter their behaviour and so on.

But no doubt a virulent infectious disease could kill huge numbers and freeze the progress of civilization for decades.

[wheresmymind]

Nanobots that can survive in virtually any environment on Earth, can utilize an incredible variety of energy sources, and can self-replicate already exist. They're called bacteria and archaea, and they effectively have taken over the world already. Actually, it was never really ours to begin with. Prokaryotes make up about half or more of the biomass on the planet. The 100 trillion or so bacteria living on and inside you outnumber your own cells by about 10 or 20 to 1.

Considering that bacteria and archaea are: A) rabidly evolving; B) Incredibly diverse metabolically; C) capable of extremely rapid self-replication in the right conditions and D) have been around for about 3 billion years and still haven't reduced the Earth to "goo," I'd say we're probably pretty safe from a man-made "gray-goo" scenario.

[TriPolar]

Originally Posted by Mijin

Depends what you mean by destroy.

Infections can wipe out species that are already on the brink of extinction. But a widely-dispersed species with 7 billion individuals, not so much. That's just based on natural variation, leave aside that humans will apply their technology to fight it, alter their behaviour and so on.

But no doubt a virulent infectious disease could kill huge numbers and freeze the progress of civilization for decades.

Well I meant infection by bots. They should be very effective at killing a human and moving on to the next poor sucker. Biological diseases tend to evolve towards a symbiotic state, though perhaps one could be designed for the purpose of extermination.

[FordPrefect]

Originally Posted by Der Trihs

Well duh, we'd placate it with liquor and nanohookerbots.

That won't work, it's better to use nanofloozybots.

[dracoi]

Originally Posted by wheresmymind

Nanobots that can survive in virtually any environment on Earth, can utilize an incredible variety of energy sources, and can self-replicate already exist. They're called bacteria and archaea, and they effectively have taken over the world already. Actually, it was never really ours to begin with. Prokaryotes make up about half or more of the biomass on the planet. The 100 trillion or so bacteria living on and inside you outnumber your own cells by about 10 or 20 to 1.

Considering that bacteria and archaea are: A) rabidly evolving; B) Incredibly diverse metabolically; C) capable of extremely rapid self-replication in the right conditions and D) have been around for about 3 billion years and still haven't reduced the Earth to "goo," I'd say we're probably pretty safe from a man-made "gray-goo" scenario.

Actually, you could argue that we're already living in the gray-goo scenario, we just label it differently. Our oxygen-rich atmosphere is a waste product of photosynthesis. Many layers of rocks are the direct result of living things - some carbonates, iron ores and fossil fuels, for example. And just try to find dirt that isn't laden with organic waste products - to find inorganic dirt, you either have to dig for it or go somewhere like the desert that hasn't been so heavily colonized by life.

So... our goo just happens to be mostly brown and we've decided to call that "normal."

[Sparky812]

Originally Posted by YogSosoth

. Even back in the 80's, when Disco was danced to unironically for pleasure within living memory,

Err... the paper you linked to was presented in May 1985, it is a well-known fact that disco died on July 12, 1979, thankfully, before it was able to destoy th Earth.

[Sparky812]

Originally Posted by FordPrefect

That won't work, it's better to use nanofloozybots.

Hey, there's a poster name/thread title hijack (or hitchhike) if I've ever seen it!


Soooo.... how likely is it that a Vogon demolition ship destroys the Earth?

[Mijin]

Originally Posted by TriPolar

Well I meant infection by bots. They should be very effective at killing a human and moving on to the next poor sucker.

Why in particular do you suppose that? Are you thinking because of the novelty of them, are you imagining them being "smarter"?

Biological diseases tend to evolve towards a symbiotic state

Well, infectious agents that persist the longest tend to be those that don't kill their hosts quickly and/or have a low mortality rate. But they do not necessarily evolve towards a symbiotic state.

And nature does cough up extremely virulent diseases from time to time; they just don't tend to last very long and they don't usually wipe out species that were not already against the ropes.

[James52637]

Originally Posted by wheresmymind

Nanobots that can survive in virtually any environment on Earth, can utilize an incredible variety of energy sources, and can self-replicate already exist. They're called bacteria and archaea, and they effectively have taken over the world already. Actually, it was never really ours to begin with. Prokaryotes make up about half or more of the biomass on the planet. The 100 trillion or so bacteria living on and inside you outnumber your own cells by about 10 or 20 to 1.

Considering that bacteria and archaea are: A) rabidly evolving; B) Incredibly diverse metabolically; C) capable of extremely rapid self-replication in the right conditions and D) have been around for about 3 billion years and still haven't reduced the Earth to "goo," I'd say we're probably pretty safe from a man-made "gray-goo" scenario.

Could you give some cites on that? I'm pretty sure quite a bit of it wasn't quite accurate.

[TriPolar]

Originally Posted by Mijin

Why in particular do you suppose that? Are you thinking because of the novelty of them, are you imagining them being "smarter"?

They could be designed to work quickly and effectively. Get in the brain, cut holes in blood vessels, get out and find another host. No need to reproduce quickly or wait around before moving on.

Well, infectious agents that persist the longest tend to be those that don't kill their hosts quickly and/or have a low mortality rate. But they do not necessarily evolve towards a symbiotic state.

Symbiotic is probably not the right word, but you've described what I was getting at.

And nature does cough up extremely virulent diseases from time to time; they just don't tend to last very long and they don't usually wipe out species that were not already against the ropes.

Diseases have to walk a tightrope where they'll be able to reproduce within a host, spread, and then kill the host. The bots would be more single purposed. They don't have to reproduce in the host, they could all be created in external factories. Build enough of them and they don't even have to spread. Just spray the planet with nanobots. It might take a bunch of them to join up in a host to do the dirty work, but as long as the factory keep producing, enough of them could get out to eventually hit everyone.

I just think this is a better approach than macro bots killing everyone with lasers. We'd be able to see the large bots and have a chance of striking back. And the large bots would need many more resources to create and maintain. Most of them will have to be busy producing the rest of them.

[YogSosoth]

Originally Posted by Senegoid

Maybe this is the site you are thinking of? Top 10 Ways to Destroy the Earth, by LiveScience. Von Neumann machines is #2 (that is, 2nd-last) on the list. (Requires JavaScript to view.)

Nope, wasn't that one. It was a stand-alone website not connected to anything else. It was dull-looking and gray, and had the apocalypses divided into categories like Any Day Now, Near Future, Distant Future, and Religious.

Originally Posted by Lemur866

The danger of lemurs destroying the Earth has been vastly overinflated.

Says the Lemur himself. How do I know you're not just trying to lull me into a false sense of security? For all I know, everyone I interact with are just 5 lemurs in a human skin suit!

Originally Posted by James52637

http://online.wsj.com/article/SB10001424052748703559004575256470152341984.html

*cough cough*

We're doomed

Originally Posted by Sparky812

Err... the paper you linked to was presented in May 1985, it is a well-known fact that disco died on July 12, 1979, thankfully, before it was able to destoy th Earth.

I think it survives to this day, waiting out its enemies in pockets of Discodome, ready to rise up should the opportunity ever present itself again

[ed anger]

Originally Posted by wheresmymind

Nanobots that can survive in virtually any environment on Earth, can utilize an incredible variety of energy sources, and can self-replicate already exist. They're called bacteria and archaea, and they effectively have taken over the world already. Actually, it was never really ours to begin with. Prokaryotes make up about half or more of the biomass on the planet. The 100 trillion or so bacteria living on and inside you outnumber your own cells by about 10 or 20 to 1.

Considering that bacteria and archaea are: A) rabidly evolving; B) Incredibly diverse metabolically; C) capable of extremely rapid self-replication in the right conditions and D) have been around for about 3 billion years and still haven't reduced the Earth to "goo," I'd say we're probably pretty safe from a man-made "gray-goo" scenario.

Originally Posted by dracoi

Actually, you could argue that we're already living in the gray-goo scenario, we just label it differently. Our oxygen-rich atmosphere is a waste product of photosynthesis. Many layers of rocks are the direct result of living things - some carbonates, iron ores and fossil fuels, for example. And just try to find dirt that isn't laden with organic waste products - to find inorganic dirt, you either have to dig for it or go somewhere like the desert that hasn't been so heavily colonized by life.

So... our goo just happens to be mostly brown and we've decided to call that "normal."

never thought of it that way, thanks both of you

[dstarfire]

Some Solutions for nanotech problems:

1. too many complex situations: complex systems are generally composed of large numbers of simpler objects/systems. the concept of nanobots is vast numbers working on individually simple tasks to produce a complex result (the same way an assembly line combines multiple simple tasks to produce a complex device).

2. Power: The one solution I saw for powering nanobots was the molecular equivalent of a ratcheted gear; it rotated easily in one direction, but not so easily in the other. Combine that with the random motion of all particles above absolute zero, and you've got a molecule-sized motor.