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

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

To hear it and every episode early and add free, plus hours of bonus content,

check out go.nebula.tv slash Isaac Arthur and use my code, Isaac Arthur.

Humanity has often lived with one foot on land and the other in the sea, but in the future,

we may build our homes in the seas, here and on other worlds.

Most of Earth's surface is water, and the most valuable property tends to be right along

the coast, so it's not surprising that the idea of artificial islands has been proposed many times.

Generally projects to accomplish them have been few in number and mixed successes at best even then.

But that's exactly the world technology has, taking

things which were impossible or impractical before, that we really want to do, and making

them possible and practical. So today we'll be looking at artificial islands, as well as other

ocean habitats, here and off Earth, from deep sea submarine habitats

to rotating space habitats designed to emulate ocean conditions.

We'll be deep diving living in the ocean, so we will be at it for a while and you might

want to drink at a snack for the journey, and please hit the like and subscribe buttons while you're

at it. Now this is SFIA, so we're not really interested in one small island built where the

sea is only a few meters beneath the low tide anyway, but rather mass manufacturer or

raising whole archipelagos or even small new continents.

That means we need to be thinking of the non-local impact.

As an example, when we talk about the tip of an iceberg, it's because ice is only slightly

less dense than water, so a big chunk of ice floating in the sea is mostly submerged

...