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I've been mulling over the idea of nanites (microscopic machines that perform work - usually to transform one material into another). I've come to the conclusion that at a macroscopic level, nanites ought to operate as we see microbial life operating.

Whether the nanite is actually coopted microbial life (e.g. bacteria reprogrammed to do something we want) or just operates like it, is irrelevant for my question.

The nanite will need an energy source (already answered in another question) and the necessary nutrients (chemical inputs). It would probably help the nanites to be suspended in some sort of working fluid (e.g. water) too.

As the nanites work, they'll use up certain elements or chemicals that are required to do their job. In order to finish their job, they'll need those chemicals constantly replaced.

How do you replenish the materials used by nanites when they're doing something?

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  • $\begingroup$ They devour the world (common apocalyptic scenario). $\endgroup$ – sumelic Mar 16 '16 at 1:16
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How do you replenish the materials used by nanites when they're doing something?

Alternative thought, you don't.

The nanites are the materials.

At least when it comes to producing something - either a finished product, or the materials for a later finished product. This wouldn't work when you want to do something other than manufacture, but I'm struggling to think of uses for nanites that isn't in some way 'eat things' and/or 'make things'.

Replenishing materials becomes a non-issue as this answer is the answer to the question of how do you manufacture nanites in the first place?

I can think of two plausible nanite life-cycles. The end result is largely the same, but the order of things is swapped around slightly.

Life-cycle A.

  1. You feed your nanites, much like you feed biological cells. They grow large and flabby.
  2. The nanites undergo binary cell fission.
  3. You encourage half of your nanites to attach themselves onto the surface of the thing being built.
  4. The nanites, using the same internal machinery used to initially build themselves, start unbuilding themselves and attaching those molecules to what's being built.
  5. Repeat.

Life-cycle B.

  1. Split your nanites into two groups.
  2. Feed both so they're large and flabby.

    2.1. Encourage one group to attach themselves onto the surface of the thing being built. It's obvious what happens here.

    2.2. Let the other group undergo binary cell fission.

  3. Repeat.

Feeding, and manufacture are both going to produce waste. Needless to say that they'll be both messy eaters and inefficient builders. The above life-cycles have the advantage of being able to separate apart the two processes. This allows us to supply the nanites with resources without interfering with the work they'll do, and tailor clean up measures accordingly.

But it comes at the cost of having to manage them. And this is a control problem.


Control.

Controlling large numbers of very small things is going to be imprecise. You won't be able to select a single nanite and direct it to a specific location. You'll be relying on swarm behaviour. Splitting nanites into groups is the easier task; if you can instruct them to form a large blob, then mechanical separation is the order of the day.

If nanites naturally like being somewhat close to each other, then they will form a blob, but you can't control the location of the blob.

Avoidance of light is a good way to direct them around as it works in liquid (caveat:transparent liquids) and with cleverly placed orthogonal lights can work in 3D and make paths to guide them.

The hard part is telling the little blighters when it's time to turn themselves into stuff. This is hard for two reasons; the thing you're building something might be something like a computer CPU that has lots of specific and precisely placed elements, and you don't want your nanites to incorrectly start building too early.

The signal to build, and what to build into needs to be very salient.

Nanites won't have access to their x, y, z coordinates. So take inspiration from biology and use combinations chemical signals. Emit a chemical from one end of your product, and another from the far end. Give the nanites a sense of smell. The ratio of one chemical to the other can infer position, and hence what the nanite should turn into. This has the added benefit of no-smells-equals-no-construction.


Waste.

Now, dealing with the waste. The waste, obviously, is the left-over parts of the nanites that weren't used.

Wastes come in two types: soluble, and non-soluble. Soluble wastes will disperse throughout your liquid. If these wastes can be consumed by the nanites, then you're golden as they'll filter out and recycle them.

Soluble wastes are a problem to the health of your nanites as they'll likely change the pH levels of the liquid. They'll react with the nanite food, the nanites themselves, or both.

Non-soluble wastes will effect the turbidity of the liquid - which may influence your ability to control the nanites. Turbid water is treated two ways; mechanically, through filtration, and chemically through reagents. Both of these could be harmful to nanites. A work-around would be to heard all the nanites to another tank/vat/etc, and process the waste separately. Always having one operating vat, and one vat being cleaned.

Using @Magnanimancer's idea of having another variety of nanite that cleans the water is a nice idea. It allows you to have a mechanical process in-situ that doesn't harm the other nanites. Suppose you have a nanite that can sense two things; the presense of other nanites, and the turbidity of the water.

If there are few nanites around; feed and multiply.

If there are many; don't.

If there's junk floating in the water, grab hold of it, don't let go, and sink to the bottom of the vat.

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    $\begingroup$ Once again, reading my mind. I wanted to ask a separate question about control, lol $\endgroup$ – Jim2B Mar 16 '16 at 1:03
  • $\begingroup$ I almost removed the entire section about control as I originally thought it wasn't related to the actual question. $\endgroup$ – user6511 Mar 16 '16 at 2:18
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It sounds like you will not only have to deal with supplying 'nutrition' for the nanites, but you'll also have to carry away whatever waste they produce after metabolizing their food. Matter doesn't like simply being destroyed, after all.

Depending on what they consume, though, I can't imagine it being much more difficult than simply dropping in the equivalent of a sugar cube every once in a while and calling it good (or, if they metabolize glucose, an actual sugar cube). Whatever remains from the process can then be collected, and through some other process (photosynthesis, perhaps?), would then be reconstituted into new glucose.

Alternatively, you could mix the nanites in with other tiny machines that actively perform the collection of excess waste and produce whatever the nanites need again. By doing this, you'll have essentially produced an artificial ecosystem. Sorta.

Eventually, though, there will be the need for some outside source of energy, but if you're using nanites as a means of production, acquiring cheap energy shouldn't be too difficult, whether through solar power, nuclear, or otherwise. Material can likely be acquired from the environment too. Glucose, for instance, is only Carbon, Oxygen, and Hydrogen, which aren't particularly difficult to find (water alone being comprised of 2/3 of those elements).

However, if you're referring to the actual materials they are building with, or altering, then, yes, that would have to be provided by some outside supply line. (Unless the nanites are permitted/instructed to deconstruct their environment when they require more minerals.) It might be analogous to providing construction workers with the wood, steel, and concrete necessary to do what they do. The ideas above are more about how the workers get their lunch, I suppose.

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  • $\begingroup$ you read my mind. I was going to ask about waste next. :) $\endgroup$ – Jim2B Mar 15 '16 at 20:31
  • $\begingroup$ Also I was thinking more about the construction materials. Previous questions on how to power nanites, explained how to provide them with the necessary energy (ala lunch). $\endgroup$ – Jim2B Mar 15 '16 at 20:33
  • $\begingroup$ Oh, in that case, I would definitely say that simply disassembling their environment is the only way to go, if they're not actively being supplied materials to work with. Of course, this is where folks have to be careful with the programming or that whole grey goo scenario might kick in, and nobody wants that. $\endgroup$ – Magnanimancer Mar 15 '16 at 20:38
  • $\begingroup$ I imagine that it is very unlikely that the environment contains the materials in the proper abundances for their needs. Also even if on a macroscopic scale the target has everything the nanite needs, remember that to the nanite, it becomes a problem of logistics. Equivalent of shipping steel across the pacific ocean, through the Panama Canal, to build skyscrapers in NYC. $\endgroup$ – Jim2B Mar 15 '16 at 20:54
  • $\begingroup$ you say that matter doesn't like being destroyed but...hey if you figure out a way to deal with waste by destroying it you will have solved your energy generation problems by a factor of a trillion or so ;) $\endgroup$ – dsollen Mar 17 '16 at 20:32
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Essentially a nanite workspace could arranged to operate somewhat like a hydroponic garden. The nanites are suspended in a tank of the working medium, and sunlight, lasers or microwaves shine on the tank to supply the energy.

A metering pump or pumps supplies nutrients and the raw materials for the items to be built, and another series of pumps or siphons draws the fluids out of the tank for filtering and recycling or processing (waste materials are processed out, while nutrients and raw materials that were not used in the first pass can be fed back into the system).

This also allows you to control the temperature and carry off waste heat from the millions or billions of nannies in the tank, while the finished product (if it is a macroscopic object) is simply lifted out once the production is complete.

While this implies that the working fluid is water, there is no need to limit yourself, depending on the nature of the nanites and the items to be created. Metallic objects like engine parts might need a slurry of metal suspended in oil, for example, and some processes might need a closed vessel that is charged with a gaseous mixture instead.

All that is needed is the working volume (usually a tank), a means to input nutrients, energy and raw materials and a means to eliminate wastes and excess heat while the process is going on.

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The closest thing we have to this is the human circulatory system, where nutrients and cells that do work are carried around together and then replenished at certain points (lungs for oxygen, etc). It seems likely that any system using nano-machines would do something similar.

Trying to have the machines stay in one place while you supply resources to them would be very hard as the movement of the raw materials would also carry the nano machines along. Instead circulate the machines through the system and have them pick up raw materials from suitable locations as they flow around.

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