If I wanted to exterminate the human race using nanotechnology, there are two methods I would think about. First method, airborne replicators which use solar power for energy and atmospheric carbon dioxide for feedstock. Second method, nanofactories which produce large quantities of synthetic greenhouse gases. Under the first method, one should imagine a cloud of nanodust that just keeps growing until most of the CO2 is used up (at which point all plants die). Under the second method, the objective is to heat the earth until the oceans boil.
For the airborne replicator, the obvious path is “diamondoid mechanosynthesis”, as described in papers by Drexler, Merkle, Freitas and others. This is the assembly of rigid nanostructures, composed mostly of carbon atoms, through precisely coordinated deposition of small reactive clusters of atoms. To assemble diamond in this way, one might want a supply of carbon chains, which remain sequestered in narrow-diameter buckytubes until they are wanted, with the buckytubes being positioned by rigid nanomechanisms, and the carbon chains being synthesized through the capture and “cracking” of CO2 much as in plants. The replicator would have a hard-vacuum interior in which the component assembly of its progeny would occur, and a sliding or telescoping mechanism allowing temporary expansion of this interior space. The replicator would therefore have at least two configurations: a contracted minimal one, and an expanded maximal one large enough to contain a new replicator assembled in the minimal configuration.
There are surely hundreds or thousands of challenging subproblems involved in the production of such a nanoscale doomsday device—power supply, environmental viability (you would want it to disperse but to remain adrift), what to do with contaminants, to say nothing of the mechanisms and their control systems—but it would be a miracle if it was literally thermodynamically impossible to make such a thing. Cells do it, and yes they are aqueous bags of floppy proteins rather than evacuated diamond mechanisms, but I would think that has more to do with the methods available to DNA-based evolution, rather than the physical impossibility of free-living rigid nanobots. The Royal Society report to which you link hardly examines this topic. It casually cites a few qualitative criticisms made by Smalley and others, and attaches some significance to a supposed change of heart by Drexler—but in fact, Drexler simply changed his emphasis, from accident to abuse. There is no reason to expect free-living rogue replicators to emerge by accident from nanofactories, because such industrial assemblers will be tailored to operate under conditions very different to the world outside the factory. But there has been no concession that free-living nanomechanical replicators are simply impossible, and people like Freitas and Merkle who continue to work on the details of mechanosynthesis have many time expressed the worry that it looks alarmingly easy (relatively speaking) to design such devices.
As for my second method, you don’t even need free-living replicators, just mass production of the greenhouse-gas nanofactories, and a supply of appropriate ingredients.
I’m not sure if this counts as an existential threat, but I’m more concerned about a biowar wrecking civilization—enough engineered human and food diseases that civilization is unsustainable.
I can’t judge likelihood, but it’s at least a combination of plausible human motivations and technology. Your tech is plausible, but it’s hard to imagine anyone wanting not just to wipe out the human race, but also to do such damage to the biosphere.
There are a few people who’d like the human race to be gone (or at least who say they do), but as far as I know, they all want plants and animals to continue without being affected by people.
There are definitely people who would destroy the whole world if they could. Berserkers, true nihilists, people who hate life, people who simply have no empathy, dictators having a bad day. Even a few dolorous “negative utilitarians” exist who might do it as an act of mercy. But the other types are surely more numerous.
If I wanted to exterminate the human race using nanotechnology, there are two methods I would think about. First method, airborne replicators which use solar power for energy and atmospheric carbon dioxide for feedstock. Second method, nanofactories which produce large quantities of synthetic greenhouse gases. Under the first method, one should imagine a cloud of nanodust that just keeps growing until most of the CO2 is used up (at which point all plants die). Under the second method, the objective is to heat the earth until the oceans boil.
For the airborne replicator, the obvious path is “diamondoid mechanosynthesis”, as described in papers by Drexler, Merkle, Freitas and others. This is the assembly of rigid nanostructures, composed mostly of carbon atoms, through precisely coordinated deposition of small reactive clusters of atoms. To assemble diamond in this way, one might want a supply of carbon chains, which remain sequestered in narrow-diameter buckytubes until they are wanted, with the buckytubes being positioned by rigid nanomechanisms, and the carbon chains being synthesized through the capture and “cracking” of CO2 much as in plants. The replicator would have a hard-vacuum interior in which the component assembly of its progeny would occur, and a sliding or telescoping mechanism allowing temporary expansion of this interior space. The replicator would therefore have at least two configurations: a contracted minimal one, and an expanded maximal one large enough to contain a new replicator assembled in the minimal configuration.
There are surely hundreds or thousands of challenging subproblems involved in the production of such a nanoscale doomsday device—power supply, environmental viability (you would want it to disperse but to remain adrift), what to do with contaminants, to say nothing of the mechanisms and their control systems—but it would be a miracle if it was literally thermodynamically impossible to make such a thing. Cells do it, and yes they are aqueous bags of floppy proteins rather than evacuated diamond mechanisms, but I would think that has more to do with the methods available to DNA-based evolution, rather than the physical impossibility of free-living rigid nanobots. The Royal Society report to which you link hardly examines this topic. It casually cites a few qualitative criticisms made by Smalley and others, and attaches some significance to a supposed change of heart by Drexler—but in fact, Drexler simply changed his emphasis, from accident to abuse. There is no reason to expect free-living rogue replicators to emerge by accident from nanofactories, because such industrial assemblers will be tailored to operate under conditions very different to the world outside the factory. But there has been no concession that free-living nanomechanical replicators are simply impossible, and people like Freitas and Merkle who continue to work on the details of mechanosynthesis have many time expressed the worry that it looks alarmingly easy (relatively speaking) to design such devices.
As for my second method, you don’t even need free-living replicators, just mass production of the greenhouse-gas nanofactories, and a supply of appropriate ingredients.
I’m not sure if this counts as an existential threat, but I’m more concerned about a biowar wrecking civilization—enough engineered human and food diseases that civilization is unsustainable.
I can’t judge likelihood, but it’s at least a combination of plausible human motivations and technology. Your tech is plausible, but it’s hard to imagine anyone wanting not just to wipe out the human race, but also to do such damage to the biosphere.
There are a few people who’d like the human race to be gone (or at least who say they do), but as far as I know, they all want plants and animals to continue without being affected by people.
There are definitely people who would destroy the whole world if they could. Berserkers, true nihilists, people who hate life, people who simply have no empathy, dictators having a bad day. Even a few dolorous “negative utilitarians” exist who might do it as an act of mercy. But the other types are surely more numerous.