Underwater communication on land and beyond

Question

So I'm thinking about an underwater civilization and everything related to it, and I got to thinking about how they would communicate over extremely long distance.

I knew that underwater species like whales and dolphins can communicate over a really long distance through vibrations and sonic waves and whatnot, but I'm focusing on what happens when they start to develop their counterpart of our telephone and radio. More so, how would it work in places without water when they eventually go beyond their natural underwater habitats.

Human vocalization wouldn't work underwater or in space, so in place of that, we developed things like extremely low-frequency transmission for communication with submarines. Would they need to build something like a room filled with water to send out their transmission?

I'm trying to have them come on land and enter a conflict with land species such as ourselves, which is why I am trying to figure out how they would communicate, since going underwater and yelling wouldn't really work when they push further inland, and definitely won't work when they start going into space.

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Edit:

I'm not as concerned for their past conflicts in the classical/medieval/renaissance era, I just assume they'd send messengers and letters and such. But I am open to interesting ideas if something does show up.

Answer 1

The problem with this setup is how radically different technological development would be underwater.

Think about all the seminal steps in human advancement that have no easy analogy underwater.

• Pottery. Can't fire a kiln underwater, underwater folks would have to find a different way to make cookware.
• Metal Working. Ditto, can't build a smelt-fire underwater. That removes a whole stack of future developments.
• Gunpowder. Doesn't work underwater. In addition to changing warfare (the obvious effect), perfecting gunpowder was one of the driving forces behind modern chemistry. Now chemistry develops in a completely different way, if at all.
• Combustion. No steam engines, no gas engines. No way to burn fossil fuels as far as I can tell.
• Electronics. Transfering small voltages is much harder in a conducting medium (seawater) than it is in air.

As I tried to answer this question, all these things got in the way of formulating an answer. I can't reasonably determine what technology these underwater folks would have available to them.

In conclusion, your underwater species needs a whole worked out tech tree, explaining how they developed roughly equivalent to modern technology without so many fundamental steps. Once you have determined that, it will become more apparent how they would communicate when on land.

Answer 2

We have to use low frequency electromagnetic waves to penetrate the water, since high frequency waves get blocked (why it's dark under the sea). The same thing applies to sea-sea communications low frequency (long wave length -> larger antennas, lower bandwidth) would be the only thing that works over long distances underwater.

Electromagnetic wave length is shorter for the same frequency under water than in air. So antennas in water are a little smaller than the matching ones in air or space.

Electromagnetic waves are really the only practical known or way to talk in space. Noting that light is electromagnetic.

Also note that large land mammals also use low frequency sound to talk over distances, so it may be that radios aren't a priority when they first get on land.

Answer 3

A bigger consideration is their tech level, how do you get them out of the stone age. the better question is how they develop metalworking without fire.

It sounds out of place but without metal or glass you are severely limited on options for communication. there are lots of technological basics that become prohibitively difficult under water, no electricity becasue no metal and no way to generate it. no glass and no ceramics although they could make optics with membrane lenses. You might need to make your species amphibious if you want them to develop advanced technology.