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The magic system of Second Earth boils down to "micromachines doing stuff". Of course, there are many layers of complexity to it.

These micromachines are produced in the bodies of sapient creatures and are subservient to them.

However, I ran into a small issue while developing the concept: communication.

Micromachines are mostly made up of organic matter and are small, comparable in size to the Kikiki Huna, the smallest know insect with a length of 150 micrometers. So, nanomachines are a few(?) orders of magnitude smaller, thus we will need different methods of communication for micro and nanomachines. We will be focusing on the former, for now.

Micromachines travel in swarms that can expand if necessary but will remain dense for the most part.

Micromachine communication is important in order for them to be able to execute complex tasks as a swarm intelligence, thus the method of communication has to be energy-efficient, fast, and reliable, while bandwidth isn't as much of a concern, as the machines themselves have limited computational power so there is no point in taking more than they can chew.

What would be the best way for micromachines to communicate?

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    $\begingroup$ Possibly related/helpful... although perhaps sound would be less manageable the smaller you get? Not sure... worldbuilding.stackexchange.com/questions/177582/… $\endgroup$
    – Qami
    May 5 '21 at 20:29
  • $\begingroup$ @Qami Thanks, though it doesn't say much about the size of the individual units that make up the swarm, which is an important factor. +1 $\endgroup$ May 5 '21 at 20:32
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    $\begingroup$ Since the "science-based" tag is present, the short answer is the same for micro- or nano-machines: "there isn't one". It's one of the reasons scifi-style nanobots are implausible. $\endgroup$ May 5 '21 at 20:35
  • $\begingroup$ @GrumpyYoungMan I choose the 150-micrometer category specifically because there are fully functional parasitic insects of that size. $\endgroup$ May 5 '21 at 20:40
  • $\begingroup$ Yes, but they don't communicate or perform coordinated actions as a swarm. Bandwidth is problematic, energy cost is problematic, finding the target to communicate with is problematic, space for the transceiver is problematic (depending on the medium), etc. $\endgroup$ May 5 '21 at 21:00
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I designed integrated circuits back when 1µm geographies were just coming into play and the industry believed that 1nm geometries were physically impossible due to gate widths getting close the the angstrom-dimensions of molecules. What did that and all the intervening experience teach me?

Humans suck at predicting the future.

But that's good news for you! Because the reality that we can build a 1nm transistor means you have several plausible options.

  • @IDNeon mentioned the most likely solution: chemical communication. There's actually a lot of options here, but if your micromachines need mobility, that means that communication is either by leaving traces (like bees do with pheromones or ants do with a scent trail, just a bit more complex...) or through physical touch. You could credibly suggest that they leave globs of recombinant DNA. The disadvantages of these solutions (assuming that's not something cool in your world... weakness are as important as strengths) are:
  1. If using something like rDNA or pheromones, then the information is almost always historical. A micromachine is leaving information that will be found by another machine at a later time. Leaving instructions for what to do in the future isn't impossible, but the latency is ugly.

  2. If using something like touch and a direct chemical interaction, then much more present information can be transmitted — but it's slow as each machine must be touched to communicate its instructions or reports.

  • But you could also get away with low-energy electromagnetic transmission (aka Radio). Oh, you'd be working at very high frequencies... but a (almost certain) limitation is that your transmitting over very short distances. Meters, at most (more likely centimeters). But that's not necessarily a bad thing. The problem with microscopic machines is that there's a veritable googleplex of them — and I think it is implausible to talk to all of them at once ... kinda.

Because what you could do is implement something like the Internet's communication protocol. Want to send out a global message? You send it (literally) to *.*.*.*.1 Each machine is programmed to repeat the message once (receiving a duplicate does not incur another repeat) to reasonably guarantee that all machines eventually get the message. Want to send it to everyone on the local subnet? You send it to (proverbially) 192.168.055.*. And if you want to communicate with just one machine, you send it to (again, proverbially) 192.168.055.215. If you're thinking, "that's just subnet masking!" You're on the right trail. Subnet globals and masking are a good starting place for describing how the little bounders can send out gazzillions of messages and coordinate themselves.

Because in the end, what you really have is a planet full of computers in the palm of your hand. And each one needs to pass all messages along while processing any message that meets the criteria of its addressing.

  • But, let's introduce one more idea. This one's more science fiction than science... but it comes from that article I linked to earlier about the 1nm transistor. From that article we read...

You see, while the 7nm node is technically possible to produce with silicon, after that point you reach problems, where silicon transistors smaller than 7nm become so physically close together that electrons experience quantum tunneling. So instead of staying in the intended logic gate, the electrons can continuously flow from one gate to the next, essentially making it impossible for the transistors to have an off state.

But what if we discovered a way, not to insulate the gate to guarantee quantum tunneling doesn't occur, but to take advantage of quantum tunneling in a predictable way?

Today's science says it can't be done — but you need to realize, you really need to realize, that in the 90s we really, truly, and honestly believed a 1nm transistor was by every law of physics IMPOSSIBLE. Which is why I don't like being limited by today's science when it comes to answering WB questions (and why I think that coming up with all the gory details is generally a bad idea). Maybe what those little beasties are doing is using your world's version of Abrason's Law of Quantum Thermal Balancing (discovered in 2245) to allow electrons to predictably tunnel across greater (much greater) than atomic distances such that the resulting excitation state of the electron (using the atomic receptor technology first developed by Sariah Lehtonnen in 2082) can be used to modulate information.2

Obligatory YouTube video


1I remember in the mid-80s where this literally could be done. I remember sending messages out to X.X.*.* such that every machine on the subnets would receive the message. I'm sure that can still be done in the UNIX world, but the "feature" has been heavily controlled by protocols since the late 80s and early 90s when SPAM moved from being a prank between friends/associates to the early versions of the very real problem it is today. But the idea supports the concepts you're creating for your world... n'est-ce pas?

2Call this "technobabble" if you want... but a lot of science fiction today is using the premise of existing technology to suggest the possibility of Clarkean Magic. The quote from We are Legion, by Dennis E. Taylor, which I reference in this meta post is a great example.

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  • $\begingroup$ Should I get my hopes up about optical rectennas? $\endgroup$ May 7 '21 at 13:55
  • $\begingroup$ I'm all in with optical rectennae, @Mephistopheles. If you can build the micromachines, you can build the nanometer antennae. The only real problem is that visible light doesn't go through much, where RF goes through almost everything. On the other hand, an X-ray transmission..... $\endgroup$ May 9 '21 at 4:08
  • $\begingroup$ Well, that would mean the machines need to be in one another's line of sight, which is easier at shorter distances. $\endgroup$ May 9 '21 at 12:51
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Neurons communicate elctro-chemically, and there are molecular machines, look those up. The best communication would be chemically, I'd say.

https://www.youtube.com/watch?v=X_tYrnv_o6A

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    $\begingroup$ Chemicals make sense. But your answer is so terse! Elaborate some. What chemicals? How is signal generated and cleared? Explain how cells do it in terms anyone interested in this sort of thing can understand, and then apply what you explain to Meph's nanites. Then you will have an upvote from me and lots of other people too. $\endgroup$
    – Willk
    May 5 '21 at 21:36
  • $\begingroup$ I'd like to get more in depth but my understanding is also at a pretty basic level. I'd say that the youtube video I did cite is a good springboard for further answers. Basically these molecular machines are doing what you're asking and they do have chemical "start/stop/hold" commands. In some cases molecular machines carry signals to other parts of the cell. What the chemicals are I don't exactly know, but they maybe are described in the original study which is discussed here: youtube.com/watch?v=Fyd4CfYfVCA $\endgroup$
    – IDNeon
    May 5 '21 at 22:44
  • $\begingroup$ links and videos are good but what if they vanish? If you understand what is in those links, make a synopsis for this answer. It can just be a few lines. As I understand WB stack the links can be for additional background material for the interested, or for skeptics who want to check sources, but that your answer can stand alone. $\endgroup$
    – Willk
    May 5 '21 at 23:07
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Colonial Nanites with Specialization:

To get this to work, I think you need nanites to function much like a symbiotic organism. Since the nanites need to be linked to their originating person, each person contains a central factory/neuroprocessing organ (possibly linked to the person's brain) that makes nanites (so they have starting programming/ID). This overcomes human to nanite communication and the limits of processing power of individual nanites.

Then, each swarm has a specialized, slightly bigger (mosquito-sized) signal-receiving nano-receiver that is essentially an antenna and optical or hormonal array. Each kind of task has either a wavelength of light (thus the glow of magic) or a hormonal signal (for an internal body task) that is tied to it. The antenna-bot gets the signal from the neuro-factory ("Human wants the table to disintegrate") sends a signal to the bots ("Move to x,y and dismantle object at x,y") and could perhaps signal back ("metal object exceeds dismantling parameters"). If the neuro-factory links with the person's optic nerve, it can use the human's eyes to observe the light pulses coming from the antenna-bot as its feedback.

The neuro-factory can get signals from the human's brain ("Don't forget the table leg!") and the process of communication goes around and around. The limitation of this is how small you can make a light receiver that can process the data you're sending (one cell in size is the minimum biologically).

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  • $\begingroup$ I think I'll merge this with JBH's answer. Another application for com-hub machines would be that the swarm's movement would be easier to control by having the swarm use them as a spatial reference. $\endgroup$ May 6 '21 at 7:29
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Morse Code

... but not as we know it.

Using optics and DNA have their own problems, but with the constant recombination of micromachines you describe, things become problematic in terms of alignment.

To handle this, you can build a micro-skeleton as a communications backbone (no pun intended). This can be addressed using standard networking techniques (JBH's answer) and by physically linked by molecular strands (IDNeon's answer). The advantage of this is that it can readily adapt to a compact or non-compact system. Your microbots are then addressed based on their position in this "tree" structure. Microbots then have only touch-range communications, but with very good latency. This also allows for large-file-transfer by DNA encoding.

This will influence the policy on parallel computing that your microbots use.


Outside the swarm

That's workable for internal communication, but what about external communication? The swarm as a whole could detect hormones or light, but hormones take a lot of processing to recognise and light takes energy to generate. Instead, the swarm can accept signals passively, in the form of sound. This is achieved by detecting variations in communication time between parts of the tree.

At this point, I'm essentially suggesting using bio-design principles and replacing cells/tissues with micromachines. Nature probably has far more elegant solutions than I've ever thought of, so I'll leave this answer here.

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