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.

We often imagine civilizations so immense they can create worlds and colonize galaxies,

and yet to fuel those immense engines of creation, they may need to harvest entire planets.

Frequently on this show, we like to talk about building various space habitats to provide us more living room than planets do, or other megastructures of unbelievable scope.

We tend to assume they are getting these from small moons or asteroids, and if they really

want tons of material, they will tap their own star for extraction first.

The reason being that a decently terraformable planet is a relatively rare item and expensive

to take apart pound for pound or kilogram for kilogram.

Indeed it's a lot more expensive pound for pound than an asteroid,

since that is a measurement of weight, not mass, and it's all about how much binding gravitational

energy an object has, which as we'll see today, tends to rise sharply with mass.

One caveat to this issue is the stars themselves, because while they are very energy intensive

to remove material from, they provide the energy for doing it themselves.

We have a magnetic lifting process called star lifting that can remove mass from stars,

including heavy metals, and lets the star power that, and the removal actually

extends the lifetime of the star.

At the same time, even after we remove hydrogen and helium from the mix, your typical star

has thousands of times more material in it than Earth has, so you can pull enough material

out of the Sun to build a few thousand

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