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.

Advanced civilizations explore the galaxy, but a Karashev 3 civilization sculpts and

rebuilds it.

The Kardefsv-Skaelov scale, first proposed by Soviet stratumor Nikolai Kartershev in 1964,

is a way of categorizing civilizations by their energy use.

A Type 1 civilization harnesses all the energy available on its home planet.

A Type 2 captures all the energy from its star.

A type 3.

It uses the energy output of an entire galaxy.

The original scale stops there, though later extensions have proposed Type 4 and beyond.

In today's episode, we'll be examining what such a civilization might look like, not just in terms of raw energy consumption, but in its infrastructure, strategy, and scope.

What kind of megastructures were to type 3 build, and when they even need to look like anything we would recognize.

We'll explore both the technological and civilizational challenges of reaching that level,

including two key paths to K3, one where fast night travel is possible, as in classic science fiction, and one where it is not, which is what science fact tilts toward.

Along the way, we'll look at the

Titanic engineering projects that could emerge, like harnessing not just a single star,

but vast swarms of stars, building entire planets from scratch, or things that make planets

look small, compacting galaxies cut down travel and communication lag, or even tugging whole galaxies

back here to keep them from flying over to cosmological adventurizing.

...