Suppose a mad engineer needs the world destroyed by next Tuesday. For efficiency's sake, he considers "Gray Goo," a hypothetical end-of-the-world scenario in which self-replicating machines devour the entire planet while building more of themselves.

Realistically, what would be required (in terms of technology, resources, schedule, etc) to successfully transform the planet into all-consuming nanomachine?

Ethics aside, what are the fundamental flaws of the Gray Goo scenario?

What are the properties of a nanomachine network engineered to become Gray Goo?

This is not so much a question on how to write a believable Gray Goo disaster as a reality check of the concept itself.

(I may be inspired to resume my mad-science degree this turns out to be feasible, so please do your best to dissuade me today :) )

  • $\begingroup$ "What would be required... ...in terms of technology" So can we grant Mr. Sie N. Tist technology sufficient to create this Gray Goo? $\endgroup$
    – Ranger
    Aug 25, 2016 at 20:20
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    $\begingroup$ To clarify: The required knowledge, if it exists. The problems, if it does not yet exist. $\endgroup$
    – Itolet
    Aug 25, 2016 at 20:22

4 Answers 4


I'll just answer one of your questions - the fundamental flaw.

The fundamental flaw is energy. Where to get it, and how to dispose of the waste heat.

Do the machines each have a nano-sized fusion reactor? Your mad scientist has to be truly amazing for that to work.

Do the machines at the top of the heap have solar cells, and then distribute the energy they gather to other machines with a network of some sort? Are the machines really that cooperative? Evolutionary selection would set in pretty quickly, I would think, and blow that cooperative structure up.

How do the machines deal with waste heat? Once you've turned the top several kilometers of the earth's crust into machines, the ones at the bottom would be cooked from below by the earth's mantle and from above by their colleagues.

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    $\begingroup$ Yup, I have yet to see a grey goo scenario that doesn't avoid the whole energy issue. (Not to mention speed issue--additive manufacturing is slow.) $\endgroup$ Aug 25, 2016 at 23:11

self-replicating machines devour the entire planet while building more of themselves

That sounds like "life." Unless you're living in space, you're surrounded by living things - bacteria, plants, other people, etc. All life is essentially trying to devour the entire planet by building more and more of themselves. We've even got mechanisms in place to help each generation be more successful than the ones before them!

...so why is the Earth still here? As @JohnFeltz mentioned, one of the big problems is energy - it takes energy to grow and reproduce and synthesize chemicals.

Another issue is that Earth is not a big ball of chocolate. There are a lot of elements, 90 of them in fact, that naturally make up the Earth. Oxygen makes up about 46% of the Earth's crust, and Silicon makes up about 28% of it. That means your gray goo will have to consist mostly of silicon and oxygen.

What to do with all those other pesky elements? That's the hard question. No two elements behave exactly the same way, and their behavior also changes based on the chemical compounds they are in - for example, our bodies have tons of hydrocarbons in them and we breathe in plenty of nitrogen, but if you put one hydrogen, one carbon, and one nitrogen together in the right way you get the extremely poisonous hydrogen cyanide.

So to start with you need a superintelligent AI running the show (and there's no guarantee that such an AI is even possible. I talked about this in a previous answer). It would need to have a complete understanding of physics and chemistry in order to understand how to break down any given material into usable components. Chances are that even then there will be elements for which there is no real use, so your best case scenario would be that there would be a giant landfill of those unusable elements and everything else has been converted.

I'd also forget about trying to do this with nanomachines, which the "gray goo" scenario typically implies. Bacteria have had a very long time to learn how to compete with each other, so nanomachines have a severe disadvantage.

One way that you could both provide enough energy and have a way to deal with unusable elements would be to discover a way to easily convert matter directly into energy and vice versa. You'll still have to deal with waste heat (and there's going to be a lot of it), but things will be much easier if you can take something like Radon, convert it into energy, and then use that energy to produce some useful carbon, iron, or whatever it is your machines need the most.

So until you master the matter->energy->matter conversions, I'd suggest trying for much simpler game of global thermonuclear war.


The main issue with the Grey Goo scenario is, as others have stated, energy. When you get right down to basics, self-replicating machines are basically just a new kind of life form, and will be under the same pressures to survive as any other living organism. You can't turn the entire planet's mass into robots without running into problems with energy sources and waste heat, so you're going to have to lower your ambitions somewhat to wiping out all organic life, turning the surface of the planet into one big solar power plant, and turning the crust into a network of geothermal power plants, with maybe some supercomputers in between. Still, an admirable goal for an aspiring mad scientist.

If you want your nanobots to take over the world, you need to build a better life form. So the question is, can human technology one-up billions of years of evolution and outcompete all life?

But all hope(?) is not lost! There are a few areas where engineers can put Mother Nature in her place, and one of those is, interestingly enough, energy. Photosynthesis is not actually all it's cracked up to be - it's good enough for life, but solar panels are about 10 times better at converting solar energy into usable power.

Evolution, for all its competitive spirit, tends to be more focused on survival and reproduction than killing. Sure, organisms kill each other all the time, but they do so because it enables them to reproduce, they don't reproduce in order to kill. Since you're engineering the goals and prime directive of this new form of life, you can give it different priorities, and most life will not be able to adapt fast enough to oppose them.

Also, you can let your machines build a computer to control their global takeover strategy, which most living organisms cannot do. Program it with your ultimate goal so that it can continue working on your objective once it has eaten you.

Unfortunately, nanobots can't construct things that fast, so destroying the world by next Tuesday is out of the question. And sooner or later pesky environmentalists and any other people who would rather the Earth not be destroyed will start to fight back. Now you're just dealing with a robot war. You can probably win that, though, provided you've planned ahead well enough.

You'll probably want to start your takeover of Earth in a place like the Sahara where silicon and sun are easy to come by. Start with self-replicating solar panels and turn the desert into your starter power source. The best part is, you don't have to give away your true intentions at this point - exploiting the desert's solar energy is a wonderful goal, and you can probably get world governments supporting you before you reveal your true intentions.

You can divert some of that energy to drilling into the Earth for geothermal power. More free energy...and more space to hide your growing robot army.

Once you have set your forces in place, it's time to reveal your hand. Now all you need to do is make more desert, and that's easy - we've been doing it for years without even trying. Slash and burn your way to victory!

Once you've converted the surface of the planet into one big solar factory and turned the inside into a network of geothermal plants, you're pretty close to exploiting all of the Earth's energy resources to their maximum potential.


converting the entire planet into "grey goo" is quite infeasible, However you don't need to consume the earth for a grey goo scenario just consuming every living thing on earth would do just fine. an analysis of the feasibility of this is outlined in this paper. (if the first link doesn't work here is another link to the paper)


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