How Would a Spacefaring Civilization Using No Electricity Communicate?

Question

I'm working on a civilization who was born out of a century-long interstellar war with an AI. So they had previously developed electrical and digital technology but now they're avoiding using any of that tech as it can be too easily hacked or manipulated with digital tools by this AI. (This civilization is the autocratic, hyper-militarized remnant of what was a vast interstellar representative democracy. Essentially a utopia.)

I've been brainstorming their technology and so far I've been thinking they'll be using distant descendants of an Analytical Engine and I was playing with all of their tech being powered by some type of hydrogen fusion internal combustion engines. I'm still not sure how much sense all of that makes, but I really like the imagery of these colossal warships with huge engines and mechanical computers. I also recently learned about fluidics and Stirling radioisotope engines from this post so that might warrant a rework of their tech.

However I think with either of those technological directions there is still a big communication problem. I haven't figured out any plausible way for interstellar or even interfleet/intership communication to work. Best I've got so far is somehow using light or being very handwavey and coming up with some crazy magnetically stabilized micro-wormhole technology or something.

Answer 1

Ravens!

Okay, so not actual Ravens - but small projectiles with a message inside of them that is 'shot' at the recipient. I'm assuming that we have no homing/tracking tech, so it would be an analogue firing solution, however if the recipient can detect it, then they can intercept it.

Bonus points if your story has FTL, then the 'message' can be transmitted at FTL speeds.

Light Signals

Morse Code, Semaphore, illumination strips - hell, even unit/patch markings all convey a message. Whether it's an actual message like Morse Code or simply identification markings - using the visible spectrum.

Now - you might say 'Oh, but with light signals, anyone can see them' - yes... but you have to be looking for them. Sometimes going old-school can really work. I think it was General Matthis (sp?) of the USMC who did an exercise and 'sunk' a US carrier - and part of his success was using low-tech runners for communications which the US aggressor fleet didn't detect and weren't looking for so didn't intercept.

Telepathy

You didn't say it wasn't possible... But that is a good means of communicating long distance - yes it's Handwaivery - but it's just as good as your wormhole idea, so I'm including it.

However...

All this said and done - the best solution would be this: Use electronic comms and accept that they are going to get intercepted and read.

You might just be about to rage at your keyboard at something so utterly stupid - but hold up.

English has a long and storied tradition of subtext. Conversations within Conversations. Meanings within Meanings. I mentioned in another question about how people would hide criminal activity in plain sight on the internet and pointed out that it's often by using words and phrases that without the knowledge of the context look innocent, it's only when you know the alternate meaning that they take a different tone.

Think of it like Encryption where your knowledge of the alternate context is the private key that unlocks the true meaning of the message.

You could even weaponize this against the AI to deliberately write messages in a way where there are 3-4 probable alternate meanings in order to create a Dilema, not a problem (that is 2-3 courses of actions that all have significant drawbacks) in order to waste time/resources from the enemy AI.

The humans, on the other hand, knowing information that only a Human could know (from first-hand experience of interpersonal relationships) would be able to decipher the correct meaning.

Answer 2

If you want to handwave long-range communications but without electricity, how about chemical lasers?

You don't have to use visible light either, not that it matters in space where there's very little scattering anyway.

Answer 3

Send a physical message. Encode it in a stable molecule in a light foil envelope. Accelerate the molecule to near light speeds with lasers. Have someone at the other end with a large receptor who is expecting some message to arrive at a certain time and place and can catch it, slowing it up with a laser.

If you are sending a message from the stars, you need huge energies to send a radio message because the signal will spread out. Shorter wavelengths spread out less, but you still need a very high beam finesse. A molecule will not spread out. Send several molecules with error correction in case something gets messed up in transit. Presumably, to keep the postal service on target, regular dummy messages will have to be passed. Load those with random data so anyone intercepting those waste a lot of time trying to decode them.

This might be the preferred way of sending messages over distances of light-years. Maybe you don't need a plot to justify it.

Answer 4

Couriers

Let's not beat around the bush here. Radio, lasers, messenger drones - no matter what technical contrivance you come up with, the fiendishly clever AI is going to be able to intercept it, read it, and send fake messages back. It's not like the AI can't blink out a message in Morse code or wire up a drone. In order to get around it, you need to do something it can't, like pass a blood test or sit down with the captain over brandy.

Messages of substance, like fleet deployment orders and after-action reports, are hand-delivered by specially trained courier pilots using small, fast ships. When they arrive, couriers are subjected to a battery of tests to prove that they are a) human and b) the specific human they claim to be. But beyond the medical tests they're also tested less formally by the ship's senior officers - does the person act like the one they're familiar with? Do they remember things that they ought to remember, like the last time they met the captain? In this way, more subtle infiltrators can be weeded out.

The downside of course is that this method is slow and doesn't scale all that well, so you will need a rigid hierarchy of command. (It would be impossible for a captain or fleet commander to be familiar with every courier in the navy, but if they only send messages to and from their immediate superior, a handful of peers under that same officer, and their own direct subordinates, it's more manageable.) It would be important to have contingencies for when a ship is out of contact and couriers can't find it, or its couriers are dead or unable to launch. But, you can be absolutely sure an AI won't be able to hack it.