Hello, SFIA audio listeners. In this month's Nebula exclusive, big alien theory,

we're asking the reason alien civilizations might be rare is because most aliens are huge.

To hear it and every episode early and ad-free, plus hours of bonus content, check out

go.nebola.tv slash Isaac Arthur and use my code, Isaac Arthur.

This episode is brought to you by Brilliant.

As we move into the future and expand off-planets, we tend to design our megastructures and habitats

to our own bipedal land-based desires. But what about our oceanic friends, like super smart

dolphins, or if we find marine life in the ocean moons of Jupiter, or if we

decide to re-engineer ourselves into more men and mermaids.

So one of our most talked about topics on this channel is the general concept that

humanity is likely to build giant space habitats as opposed to simply terraforming and colonizing other planets,

and today we will be discussing that notion in the context of building oceanic and aquatic habitats

in space. We will introduce some new megastructures, like a hydro shell, which allows truly

huge aquatic environments, dwarfing planets but avoiding crushing water pressures.

We will be looking at this in terms of a few options for gravity, microgravity, gravity

simulated by rotation, natural gravity, and artificial gravity. We will be looking at scales

from small habitats up to planet-sized ones, and even ones dwarfing planets in scope.

We will also be looking at purposes, whether it's a civilization that's aquatic in nature,

or it's more of a preserve, such as if we built large marine habitats as nature preserves,

rather than for us to live in, or for highly uplifted dolphins or whales to live in. We will also play with

some interesting features you might have in these, like vertical reefs or submarine islands inside

or under the water. Now to begin our discussion, there's two critical concepts we need to understand.

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