So, grey goo isn't exactly the most useful thing from a military standpoint, not just because of high-entropy and metastable materials that you can't get chemical energy out of, but also that:

Me: Can we have some realistic grey goo at home?
Mom: We already have realistic grey goo at home.
Realistic grey goo at home: Literally just COVID-19

While it's true that this peculiar little thing managed to bring humanity to its knees without trying, I want something that while only brings down "smaller" things like humans and tanks, it does that preferably within seconds or a minute, not months.

Now, "bring down" here means destroying/impeding an object's capability to harm you. So, if the human is in a state where they can't fire their weapon for whatever reason and the tank's main weapon and gun turret becomes inoperable, they've been brought down.

But how are a swarm of micrometre and nanometre robots supposed to be able to quickly disable both organic military personnel and inorganic military hardware?

  • $\begingroup$ Why do you think the grey goo you've described isn't a WMD? Is the disabling action only temporary? $\endgroup$ Jun 24, 2020 at 17:25
  • $\begingroup$ @JBH It can't chain reaction. Sure, if you create a machine that mass-produces the swarm, then that machine could be considered a WMD. $\endgroup$ Jun 24, 2020 at 17:27
  • $\begingroup$ Bear with me as I play devil's advocate. A nuclear bomb can't "chain reaction." It explodes, and that's it. Maybe a virus is a WMD using that definition, but mustard gas wouldn't be. Are your nanites programmed to die after a day or two? And as I asked, is the disabling action only temporary? Perhaps more accurately, if I describe a solution that disables everything for only 24 hours, have I met your expectations? Or if I describe something that affects a permanent change, have I failed your expectations? I'm a bit confused by what you're looking for. $\endgroup$ Jun 24, 2020 at 18:05

3 Answers 3


EMP nanites: The premise here is that some place has been seeded with self-replicating (grey goo-like) nanites who's function is a bit like tiny capacitors. Maybe they consume chemical energy from the environment, or perhaps a nanite no longer replicating behaves like a tiny solar panel. They each make a new nanite, then store excess energy. I don't know exactly how tiny nanomachines would create an EM pulse, but at a predetermined signal, a receptive nanite would trigger a pulse, which would signal any partly signalled nanites to also pulse. Each pulse would be individually tiny but collectively massive. If the nanites were inside a soldier, they might kill him from the disruption to his nervous system (again, not sure of exact method, so effects could vary). electronic systems could fry, some advanced weapons malfunction, etc. Modern militaries have been working hard to shield from EMP, so you could make this as effective or ineffective as you wanted for story purposes.

  • The nanites could be the delivery method for a whole class of EMP weapons, but self-replicating nanites could be seeded lightly and build up over time like a self-replicating minefield. Or nanites could be manufactured, then charged nanites sprayed in an area (perhaps designed to stay suspended in the air, yet electrostatically prompted to maintain themselves in a cloud)???
  • If this is too subtle, how about nanites that produce explosive and grow into balls or nodules? Pick your activation method of choice. I like the idea of a soldier using a radio and setting off a mass of tiny explosions all over his vehicle, but it could be contact-triggered (landmine-like) or chemosensitive (reach a critical size and explode in the presence of petroleum exhaust) or maybe even auditory (explode when a certain phrase is said in Russian, say).

They home in on areas of gas movement, and occlude those areas.

Your grey goo can sense gas movement, and especially gas different from ambient temperature. The nanobots move towards areas of gas movement. When they reach such an area they pack in, occluding movement of the gas. They are attracted as long as there is moving gas.

This means the exhaust of internal combustion engines and heat exchangers / radiators of other powered devices. This means the respiratory tracts of animals that breathe. Possibly digestive tracts to a lesser extent.

Preventing gas exchange / heat exchange is rapidly disabling to breathing animals and machines. This mode of attack by the goo does not require much sophistication. It could be guarded against with a fair bit of inconvenience.


Your Nanites could produce an accelerated entropy field. They absorb the energy directly from material for their operation. Since they exist at a molecular level, they absorb energy at an atomic level. This accelerates aging of organic material. Accelerates decay of inorganic material.


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