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So, I'm interested in a humanoid civilisation, only it develops underwater, in a world with no ground above sea level. I want to know, considering ignition with a spark would be, well since, fire and water don't mix, how would they create explosives?

What materials would they use?

boboranonymous
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    Unless the humanoids came from elsewhere, I wouldn't expect humanoids at all. – Monty Wild Oct 26 '23 at 03:55
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    Can you tell us what you've tried to find out and what level of technical sophistication your society has developed? The more I think about it the more show stoppers I see, e.g. no electrolysis at high pressure, not sure if stone flint lives in ocean floor geology but maybe quartz and thus piezo electric igniters, chemistry of any kind is quite different to deal with. But deep ocean is unfamiliar territory for humans, so I'm not used to thinking about how stuff would work. – Nolo Oct 26 '23 at 04:15
  • Around our technology, if that would be possible. Otherwise, any technology level where it would work. I hope that's not too vague – boboranonymous Oct 26 '23 at 04:16
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    Alright, but our level of technology did not develop under water, so our set of options for figuring stuff out and engineering things is quite different. So there's a very large hump of missing knowledge to overcome. With much more thought and theory it may be possible to derive a sort of way to get somewhere close to there from here. I'll think on it a bit and try later. :-) – Nolo Oct 26 '23 at 04:19
  • If it doesn't get closed. Be sure to read about how to ask questions here and update with the kind of information we need to help you get a reasonable answer. – Nolo Oct 26 '23 at 04:20
  • True. Maybe i should reword it to say they've had the same amount of years for development, so ~ 200 000 years or so. Of course, majority of that time was as stone-age nomads, so the actual "science" and building phase was a lot later. Of course, as you stated, we developed in air not water, obviously very different things. – boboranonymous Oct 26 '23 at 04:23
  • Assuming the existence of any underwater caves that aren't completely filled with water, it's possible that inhabitants "reverse diving" into these areas could lead to the discovery of similar materials and processes like the ones that exist in our world - there are plenty of devices that detonate fine underwater which would be impossible to manufacture completely underwater.

    For example the discovery of a bat cave / guano would be a pretty big step towards the discovery of gunpowder, add a watertight container and piezoelectric detonator- boom!

    But in general dry areas = more options.

     – betweenthelines Oct 26 '23 at 10:26
  • The development of watertight devices wouldn't be a big ask in the scenario mentioned above, if you consider that discovering such spaces would likely lead to the development of SCABA (Self Contained Anhydrous Breathing Apparatus) devices for longer periods of sustained out-of-water exploration. – betweenthelines Oct 26 '23 at 10:32
  • I don't want to vote to close, but this question is too vague. You're trying to create your underwater species in Humanity's image. Since most general explosives available to humans won't work underwater, it's more likely that your species would create a number of solutions for different purposes (all of which we'd use explosives for, but they can't). Therefore, Please [edit] your post to provide a specific example of what the "explosive" would be used for. If you are tempted to provide multiple, disparate examples, ask them as separate questions, instead, one at a time. – JBH Oct 26 '23 at 17:51
  • I am not smart enough to back this up. But I wonder if such a civilization would just jump to nuclear devices of some sort. Living effectively in an atmosphere (water) that blocks the usual chemical reactions. Nuclear would still work under water wouldn't it? – Trevor Oct 26 '23 at 18:37
  • Note TheDemonLord's comment on hand waving. Getting more specific depends on the question. https://worldbuilding.stackexchange.com/questions/250760/how-would-a-civilisation-that-develops-underwater-create-explosives#comment-770330 – Nolo Oct 26 '23 at 18:56
  • @L.Dutch please can you review my revised answer to this question so that it can be reopened, reposted or binned. thx – Slarty Oct 26 '23 at 19:14
  • They'd start from electric eels-ish usages, develop them into something like bombs which spread voltage on higher distances. I guess, they could eventually fry or change a big radius sphere of water into some less dense and weak molecules which would implode after seconds. Maybe implosion would be easier to gain in such conditions - I wonder - just my imagionation here. – Peter.k Oct 26 '23 at 21:15
  • @john That doesn't seem like a duplicate at all. This is asking how an underwater civilization would create explosives, in particular. The one you linked has one kind of off-hand reference that says it would be easy, but not how (it was also quoting fiction). The rest of it is about other technologies. – JamieB Oct 27 '23 at 03:23
  • @Trevor all nuclear explosion mechanisms known rely on chemical explosives for initiation. – KerrAvon2055 Oct 27 '23 at 05:18
  • @JamieB a main focus of that question is could they create fire and chemistry, which is what is needed for this question. before they can make explosive they need those first. – John Oct 27 '23 at 10:32
  • @Trevor I think nuclear should work underwater – boboranonymous Oct 30 '23 at 02:17
  • @John just putting things out there, assuming they could harness alkali metals using perhaps electrochemistry, could they seal them in a watertight container, and release them into water when needed, to "explode"? – boboranonymous Oct 30 '23 at 02:22
  • @KerrAvon2055 But as I understand it, that chemical explosion is just to smash the 2 opposing elements together faster. Tons of things could do that, even a pressure chamber. – Trevor Oct 30 '23 at 17:22
  • electrochemistry requires developing electricity and and isolation based chemistry both basically impossible underwater. – John Oct 30 '23 at 19:48

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I would expect underwater technological evolution to have gone without fire which is one of the biggest parts and driving forces behind our own human technology. Chemistry, metallurgy etc,. wouldn't really exist or be severely hampered.

They can still create explosive type forces using hydraulics and kinematic transmission which would be highly advanced within the limits of their resources. Mantis shrimp for instance pack a crazily powerful strike underwater. So the same forces which allow clams to move, mantis shrimp to punch and enable jet propulsion in squids would all be useful.

Kilisi
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  • I'll give you that chemistry is hard and alien to us under water, but is it off the table? – Nolo Oct 26 '23 at 18:50
  • @Nolo I would think so, I can't imagine how they would work out the periodic table or any of the basics in a salt water medium – Kilisi Oct 26 '23 at 20:19
  • @Nolo the big problem is it is easy ot isolate solutions on land, you can use containers that you can mix and pour from and you can evaporate things to get solids, nether work underwater. – John Oct 30 '23 at 19:50
  • @John yes, I recognize that. Any kind of solution would be incredibly complicated and would almost certainly not involve drying things. However, I have to assume there are interesting things to learn by pushing knowable boundaries within those constraints. For example, the fact that lighting is electricity and it's the same thing as static shocks on door handles, and moreover, that it's intimately related to magnetism, were revelations for us. But we can assume that underwater civilization might know something about electric eels and be curious about biology. – Nolo Oct 30 '23 at 20:31
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    @Nolo but without an insulator or metals experiments can't be done, water is too good a conductor. you can't even build a simple battery or wire underwater. static doesn't build up underwater so they wouldn't even have that to learn from. there have been a lot of questions about technology underwater. – John Oct 30 '23 at 20:45
  • Their technology might be highly advanced but would have totally different focus than ours. Eg Polynesians had no metal, but could build a voyaging canoe and navigate for thousands of miles of open ocean confident of arriving where they were heading for – Kilisi Oct 30 '23 at 22:48
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Possibly the same, possibly different

Okay - so a wonderfully 50/50 answer.

Well - let's look at why it might be the same - consider Nitroglycerine. It's one of the older explosive compounds and it has a medicinal use.

The Medicinal use part is important because it gives an in-world justification as to why a civilization that doesn't use gunpowder, would 'discover' an explosive compound. Once discovered and various uses are found, more explosive compounds would likely be found and the process better understood etc.

So - why start with Nitroglycerine? Well, apart from the plausibility of it's discovery - it's an explosive that is shock-sensitive. That means, no flame or electricity needed to set it off - perfect for an underwater environment.

It's shock-sensitivity also provides a justifiable reason as to why additional research and discovery of new explosive compounds would happen.

That's the evolutionary path of the discover of an explosive compound and why they would seek to discover more.

However, where things will rapidly diverge is that underwater, the propagation of a blast wave is much different than in air - Explosives can be much more destructive because of the multiple impulses.

This means that the types of Explosive used, how they are used etc. will be significantly different. You would likely see less push towards more explosive power, you wouldn't see the development of things like EFPs - although you may still see shaped charges to maximize the effect of the hydraulic forces/Cavitation from the water.

In short - once shock-sensitive explosives are 'discovered' - via Medical research first stop would be to make them more stable, then other ways to initiate the explosive. From there, the properties of being underwater would cause a divergence in the research paths.

TheDemonLord
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  • Good answer. I suspect that chemical engineering is the biggest hurdle. That's what drew a lot of blanks for me. Though I admit little knowledge of chemistry to begin with. How then would we produce nitroglycerine under water? Or are there alternatives to consider? Lots of stuff races around, super saturation, deep sea vents and so on. :D Can you provide any hints that may help? – Nolo Oct 26 '23 at 18:43
  • I know that iodide contact explosives come out of a wet precipitate and must be dried to work, so we'd have to steer around such problems. – Nolo Oct 26 '23 at 18:44
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    @Nolo - I agree that it's the biggest hurdle - however, since the OP has indicated 'around our tech level' - I'm inferring a handwave around the chemical engineering challenge - that they either have 'clean rooms' or 'non-reactive rooms' or some other means of preparing materials underwater – TheDemonLord Oct 26 '23 at 18:52